WO2014155451A1 - Image coding device and image coding method - Google Patents
Image coding device and image coding method Download PDFInfo
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- WO2014155451A1 WO2014155451A1 PCT/JP2013/007050 JP2013007050W WO2014155451A1 WO 2014155451 A1 WO2014155451 A1 WO 2014155451A1 JP 2013007050 W JP2013007050 W JP 2013007050W WO 2014155451 A1 WO2014155451 A1 WO 2014155451A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
- H04N19/12—Selection from among a plurality of transforms or standards, e.g. selection between discrete cosine transform [DCT] and sub-band transform or selection between H.263 and H.264
- H04N19/122—Selection of transform size, e.g. 8x8 or 2x4x8 DCT; Selection of sub-band transforms of varying structure or type
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
- H04N19/136—Incoming video signal characteristics or properties
- H04N19/14—Coding unit complexity, e.g. amount of activity or edge presence estimation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
- H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
- H04N19/176—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a block, e.g. a macroblock
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
- H04N19/61—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding in combination with predictive coding
Definitions
- the present disclosure relates to an image encoding device that can selectively perform orthogonal transform in an encoding operation.
- standardization of compression technology is also important for interoperating compressed image data.
- H.264 of ITU-T International Telecommunication Union, Telecommunication Standardization Division
- 261, H.H. 263, H.M. H.264 and ISO / IEC International Organization for Standardization
- MPEG-1, MPEG-3, MPEG-4, MPEG-4AVC and the like.
- HEVC High Efficiency Video Coding
- each picture to be coded is divided into coding unit blocks, and the amount of information is compressed by reducing redundancy in the time direction and the space direction for each block.
- inter-frame predictive coding for the purpose of reducing temporal redundancy, motion is detected and a predicted image is created in block units with reference to the front or rear picture, and the obtained predicted image and encoding target are obtained. The difference image with the block of is acquired.
- intra prediction encoding for the purpose of reducing spatial redundancy, a prediction image is generated from pixel information of surrounding encoded blocks, and the obtained prediction image and the block to be encoded are Get the difference image.
- orthogonal transform such as discrete cosine transform and quantization on the obtained difference image.
- luminance component information and color difference component information are converted into frequency component information.
- quantization is performed such that the higher the frequency region is, the wider the quantization range is, the information that is difficult to be recognized by the human eye is omitted, and the deterioration is difficult to understand by the human eye.
- the amount of information is compressed by generating a code string using variable length coding.
- HEVC see Non-Patent Document 1
- one block size is selected from among four candidates by cost determination within a range that can be divided by the quadtree structure for each block to be encoded.
- quantization is performed with a quantization width determined by multiplying the quantization parameter set for each block and the quantization matrix set for each picture.
- JCTVC-L1003 High Efficiency Video Coding (HEVC) text specification draft 10 (01/2013)
- the orthogonal transformation target block is uniquely determined in order to simply reduce the calculation processing amount, depending on the type of image, there is a risk that subjective image quality may be deteriorated due to noise generated by the orthogonal transformation and quantization. .
- the present disclosure provides an image encoding device and an image encoding method capable of improving subjective image quality and reducing the amount of calculation processing.
- An image encoding device is an image encoding device that encodes an input image, and for each determination block including a plurality of pixels included in the input image, the determination block includes a specific area including a character or a line drawing
- a residual coefficient is output by selectively performing orthogonal transform of the determination block in a determination unit that determines whether or not and a transform processing unit adaptively selected from a plurality of transform processing units.
- An orthogonal transform unit and when the determination unit determines that the determination block is a specific area, the orthogonal transform unit always orthogonalizes the determination block for each conversion processing unit set to a block size of 4 ⁇ 4 pixels. Perform the conversion selectively.
- the image coding apparatus According to the image coding apparatus according to the present disclosure, it is possible to improve the subjective image quality and reduce the amount of calculation processing.
- FIG. 1 is a block diagram showing an image coding apparatus according to Embodiment 1.
- FIG. 2 is a flowchart showing determination of a specific area and orthogonal transform processing according to the first embodiment.
- FIG. 3 is a block diagram showing an image coding apparatus according to Embodiment 2.
- FIG. 4 is a flowchart showing determination of a specific area and orthogonal transformation processing according to the second embodiment.
- FIG. 5 is a flowchart illustrating specific area determination and orthogonal transform processing according to a modification of the second embodiment.
- FIG. 6 is a block diagram showing an image coding apparatus according to Embodiment 3.
- FIG. 7 is a flowchart showing determination of a specific region, orthogonal transform processing, and setting of a quantization parameter according to the third embodiment.
- FIG. 1 is a block diagram showing an image coding apparatus according to Embodiment 1.
- FIG. 2 is a flowchart showing determination of a specific area and orthogonal transform processing according to the first embodiment.
- FIG. 8 is a flowchart showing the setting of the quantization parameter according to the third embodiment.
- FIG. 9 is a block diagram showing an image coding apparatus according to Embodiment 4.
- FIG. 10 is a flowchart showing specific area determination, orthogonal transform processing, and quantization parameter setting according to the fourth embodiment.
- FIG. 11 is a flowchart illustrating specific area determination, orthogonal transform processing, and quantization parameter setting according to a modification of the fourth embodiment.
- FIG. 1 is a block diagram of an image coding apparatus 100 according to the present embodiment.
- the image encoding apparatus 100 divides an image input in units of pictures into blocks and performs an encoding process in units of blocks to generate a code string.
- the image encoding device 100 includes a picture memory 101, a block division unit 102, a specific area determination unit 103, a difference calculation unit 104, an orthogonal transformation unit 105, a quantization unit 106, An inverse quantization unit 107, an inverse orthogonal transform unit 108, an addition operation unit 109, a predicted image generation unit 110, and a code string generation unit 111 are provided.
- the picture memory 101 stores the input image signal in units of pictures.
- the picture memory 101 receives a read command from the block division unit 102, the picture memory 101 outputs an image signal related to the read command.
- the input image signal is image data indicating a still image on a paper surface such as a newspaper or a magazine.
- the input image signal may be moving image data indicating a video in which characters or line drawings are multiplexed, for example, a video including subtitles.
- the block dividing unit 102 divides the image signal input from the picture memory 101 into blocks of, for example, 64 ⁇ 64 pixels called a coding unit (CU) that is an encoding processing unit.
- CU coding unit
- the block dividing unit 102 further divides the CU into, for example, 8 ⁇ 8 pixel blocks called prediction units (PUs) that are processing units for predictive image generation.
- PUs prediction units
- the CU describes a block of 64 ⁇ 64 pixels, but a block size of 32 ⁇ 32 pixels, 16 ⁇ 16 pixels, or 8 ⁇ 8 pixels may be used.
- the PU has been described as an 8 ⁇ 8 pixel block. However, for example, another size such as 8 ⁇ 16 pixels or 8 ⁇ 4 pixels may be used.
- the PU has the same size as the block size of the CU, or a size obtained by dividing the CU into two or four.
- the specific area determination unit 103 determines, for each determination block including a plurality of pixels included in the input image, whether or not the determination block is a specific area including a character or a line drawing. Specifically, the specific area determination unit 103 acquires an image feature amount from the encoding target picture output from the block division unit 102 and determines whether or not the predetermined area is a specific area for each predetermined determination block.
- the specific area refers to an area including characters or line drawings. In an area drawn with a character or line drawing, an edge is likely to occur between the character or line drawing and the background image. Therefore, the specific area is also an area including an edge.
- 4 ⁇ 4 pixels are always selected as a block size (TU size) called a transform unit (TU) that is a unit of orthogonal transformation.
- the TU size includes blocks of 32 ⁇ 32 pixels, 16 ⁇ 16 pixels, 8 ⁇ 8 pixels, and 4 ⁇ 4 pixels.
- the TU size of the determination block determined not to be the specific region is selected from the above blocks of 32 ⁇ 32 pixels to 4 ⁇ 4 pixels, which has high encoding efficiency such as orthogonal transform and quantization.
- the TU has the same size as the CU block size or a smaller block size.
- the subsequent processing is performed in units of blocks of CU, PU, and TU depending on the processing content.
- the difference calculation unit 104 generates a difference image signal that is a difference value between the PU unit image signal input from the specific region determination unit 103 and the PU unit prediction image signal input from the prediction image generation unit 110.
- the difference calculation unit 104 outputs the generated difference image signal to the orthogonal transformation unit 105.
- the orthogonal transform unit 105 outputs a residual coefficient signal by selectively performing orthogonal transform of the determination block in a transform processing unit adaptively selected from a plurality of transform processing units. Specifically, the orthogonal transform unit 105 generates a residual coefficient signal by performing orthogonal transform on the difference image signal input from the difference calculation unit 104 in units of TUs.
- the orthogonal transform unit 105 can select whether or not to perform orthogonal transform when the transform processing unit (TU) is 4 ⁇ 4 pixels. That is, the orthogonal transform unit 105 selectively performs orthogonal transform when the TU size is 4 ⁇ 4 pixels.
- the orthogonal transform unit 105 can generate and output a residual coefficient signal by performing orthogonal transform on the difference image signal (operation A).
- the orthogonal transform unit 105 can output the difference image signal as a residual coefficient signal without performing orthogonal transform on the difference image signal (operation B). For example, the orthogonal transform unit 105 selects one of the operation A and the operation B that has better coding efficiency based on a predetermined cost determination.
- the orthogonal transform unit 105 When the specific region determination unit 103 determines that the determination block is a specific region, the orthogonal transform unit 105 always orthogonalizes the determination block for each transform processing unit (TU) set to a block size of 4 ⁇ 4 pixels. Residual coefficients are output by selectively performing the transformation. That is, the orthogonal transform unit 105 determines whether or not to perform orthogonal transform for each TU included in the determination block. For each TU, the orthogonal transform unit 105 generates and outputs a residual coefficient signal by performing orthogonal transform on the difference image signal when performing (i) orthogonal transform, and (ii) when not performing orthogonal transform. The difference image signal is output as a residual coefficient signal as it is.
- TU transform processing unit
- the orthogonal transform unit 105 uses the determination block in a conversion processing unit selected from a plurality of predetermined conversion processing units (TU).
- the residual coefficient is output by selectively performing the orthogonal transformation.
- the orthogonal transform unit 105 selects one block from blocks of 32 ⁇ 32 pixels to 4 ⁇ 4 pixels. Note that when a 4 ⁇ 4 pixel block is selected as a transform processing unit, the orthogonal transform unit 105 can select whether or not to perform orthogonal transform as described above.
- the quantization unit 106 quantizes the residual coefficient signal input from the orthogonal transform unit 105 in units of TUs. At this time, the quantization unit 106 generates a quantized residual coefficient signal by quantizing the residual coefficient signal according to a quantization value (quantization parameter) and a quantization matrix set in units of CUs. .
- the inverse quantization unit 107 generates a reconstructed residual coefficient signal by performing inverse quantization on the quantized residual coefficient signal input from the quantization unit 106 in units of TUs.
- the inverse quantization unit 107 outputs the generated reconstructed residual coefficient signal to the inverse orthogonal transform unit 108.
- the inverse orthogonal transform unit 108 generates a reconstructed difference image signal by performing inverse orthogonal transform on the reconstructed residual coefficient signal input from the inverse quantization unit 107 in units of TUs. Then, the inverse orthogonal transform unit 108 outputs the generated reconstructed difference image signal to the addition operation unit 109.
- the inverse orthogonal transform unit 108 can select whether to perform inverse orthogonal transform when the TU size is 4 ⁇ 4 pixels. Specifically, when the reconstructed residual coefficient signal is input from the inverse quantization unit 107, the inverse orthogonal transform unit 108 is obtained by orthogonally transforming the reconstructed residual coefficient signal in the orthogonal transform unit 105. By performing inverse orthogonal transform on the reconstructed residual coefficient signal, a reconstructed differential image signal is generated and output. Further, when the reconstructed residual coefficient signal is obtained without performing orthogonal transform in the orthogonal transform unit 105, the inverse orthogonal transform unit 108 reconstructs the reconstructed residual coefficient signal as it is without performing inverse orthogonal transform. The difference image signal is output to the addition operation unit 109.
- the addition operation unit 109 generates a reconstructed image signal by adding the reconstructed difference image signal input from the inverse orthogonal transform unit 108 and the predicted image signal input from the predicted image generation unit 110 in units of PUs. To do.
- the predicted image generation unit 110 uses the reconstructed image signal input from the addition operation unit 109 to the PU unit image signal input from the specific region determination unit 103, and performs intra-screen prediction (intra prediction) or PU unit.
- a prediction image is generated by performing inter-screen prediction (inter prediction).
- inter prediction inter prediction
- the predicted image generation unit 110 uses a reconstructed image signal of a past picture that has already been encoded.
- intra prediction the prediction image generation unit 110 uses a reconstructed image signal of the same picture that has already been encoded and is adjacent to the PU to be encoded. Note that if the input image input to the image coding apparatus 100 is a still image composed of only one picture, there is no past picture, and therefore only intra prediction is always used.
- the code string generation unit 111 performs variable-length coding and arithmetic on the quantized residual coefficient signal, the quantization matrix signal, and other encoded information signals necessary for decoding processing input from the quantization unit 106.
- a code string is generated by encoding.
- FIG. 2 is a flowchart showing determination of a specific region and orthogonal transformation processing according to the present embodiment.
- the specific area determination unit 103 determines, for each determination block including a plurality of pixels included in the input image, whether the determination block is a specific area including a character or a line drawing (S110). Specifically, the specific area determination unit 103 calculates an image feature amount from a determination block included in the encoding target block (CU) output from the block division unit 102, and determines whether the determination block is a specific area. Determine whether or not.
- the specific area determination unit 103 calculates, for example, information based on a luminance component as an image feature amount.
- the luminance component of a character or line drawing is generally concentrated on high luminance and low luminance, and the luminance changes extremely in a small range. Therefore, the inclination of the luminance component between adjacent pixels tends to increase.
- the specific area determination unit 103 calculates, for example, a luminance difference between adjacent pixels as an image feature amount.
- the specific area determination unit 103 indicates that the determination block is a specific area when the ratio of pixels in the determination block and the ratio of pixels having a large luminance difference between adjacent pixels is equal to or greater than a predetermined ratio. judge.
- the specific area determination unit 103 calculates a difference in luminance value between adjacent pixels. Then, the specific area determination unit 103 determines whether or not the calculated difference is greater than a predetermined first threshold value. When it is determined that the pixel is larger than the first threshold, the adjacent pixel is determined to be a pixel having a large luminance difference. The specific area determination unit 103 compares the difference between the luminance values with the first threshold value for all the pixels included in the determination block.
- the first threshold value is, for example, a value that is 50% or more of the difference between the minimum value and the maximum value of the luminance values.
- the specific area determination unit 103 calculates a ratio of pixels determined to be pixels having a large luminance difference in the determination block. Then, the specific area determination unit 103 determines whether or not the calculated ratio is greater than or equal to a predetermined ratio (second threshold). For example, the specific area determination unit 103 determines whether or not the pixel ratio is equal to or greater than the second threshold. When the pixel ratio is equal to or greater than the second threshold, the specific area determination unit 103 determines that the determination block is a specific area.
- the second threshold is a value of 20% or more, for example.
- the luminance component is used as the reference for the image feature amount.
- any reference may be used as long as it is information calculated from the picture to be encoded.
- the specific area determination unit 103 sets the size of the determination block to 8 ⁇ 8 pixels, for example.
- a determination block determined to be a specific region is orthogonally converted in units of 4 ⁇ 4 pixel conversion processing.
- the size of the determination block may be 4 ⁇ 4 pixels or more.
- the determination block for determining the specific area is preferably a block composed of 8 ⁇ 8 pixels.
- the specific area determination unit 103 When it is determined that the determination block is a specific area (Yes in S110), the specific area determination unit 103 always selects a 4 ⁇ 4 pixel block as the TU size (S120). On the other hand, when it is determined that the determination block is not the specific area (No in S110), the specific area determination unit 103 selects any one of 32 ⁇ 32 pixels to 4 ⁇ 4 pixels as the TU size (S130).
- the TU size is determined based on, for example, the encoding target block. For example, a small TU size is selected for a complex image and a large TU size is selected for a simple image.
- the orthogonal transform unit 105 selectively performs orthogonal transform of the determination block for each selected TU (S140). For example, when the orthogonal transformation unit 105 selects to perform orthogonal transformation when the TU size is 4 ⁇ 4 pixels, the orthogonal transformation unit 105 performs orthogonal transformation on the difference image signal to generate and output a residual coefficient signal. . In addition, when the TU size is 4 ⁇ 4 pixels and the orthogonal transform unit 105 selects not to perform the orthogonal transform, the orthogonal transform unit 105 outputs the difference image signal as it is as a residual coefficient signal.
- the orthogonal transform unit 105 when the TU size is not 4 ⁇ 4 pixels, the orthogonal transform unit 105 generates and outputs a residual coefficient signal by performing orthogonal transform on the difference image signal.
- the orthogonal transform unit 105 receives the TU output from the specific region determination unit 103, and determines whether or not the TU size is 4 ⁇ 4 pixels.
- the specific area determination unit 103 determines the TU size.
- the present invention is not limited to this.
- the specific area determination unit 103 may determine 4 ⁇ 4 pixels by overwriting the TU size.
- the block division unit 102 determines each block size.
- the CU and PU sizes may be determined according to the TU size determined by the specific area determination unit 103.
- the determination block size is 8 ⁇ 8 pixels, but other predetermined sizes may be used as long as the size is 4 ⁇ 4 pixels or more. This predetermined size may be set depending on the number of pixels occupying one character in the acquired input image.
- the specific area determination unit 103 may determine the determination block size so that one character in the input image fits in one determination block.
- the size of characters in the input image depends on the screen resolution of the input image. For example, when encoding a magazine or a newspaper, when the screen resolution is determined, the character size is often determined naturally. Therefore, by setting the determination block according to the screen resolution, it is possible to fit one character into one determination block.
- the specific area determination unit 103 may determine the determination block size according to the screen resolution of the input image. Specifically, the specific area determination unit 103 determines the determination block size to be 8 ⁇ 8 pixels when the screen resolution of the input image is 1920 ⁇ 1080 (full HD) or more and 3840 ⁇ 2160 (4K2K) or less. May be. Thereby, it is possible to fit one character in the determination block of 8 ⁇ 8 pixels. In this case, the number of determination blocks including edges can be reduced.
- the specific area determination unit 103 may determine the determination block size to be a non-fixed size with respect to the input image, such as a CU size. That is, the specific area determination unit 103 may set the size of the determination block to N ⁇ N pixels (N is an integer of 4 or more). As an example, N is 8.
- the TU size of the determination block determined to be a specific region by the specific region determination unit 103 is always limited to a 4 ⁇ 4 pixel block.
- the specific area there are many high-frequency components around the character or line drawing. Since orthogonal transformation and quantization tend to lose high-frequency component information, noise is likely to occur in the vicinity of a character or line drawing.
- the processing block can be omitted by always uniquely setting the TU size of the determination block determined to be the specific area as a 4 ⁇ 4 pixel block. Therefore, the amount of calculation processing can be greatly reduced for input images with more characters or line drawings.
- the image encoding apparatus is an image encoding apparatus 100 that encodes an input image, and for each determination block including a plurality of pixels included in the input image, the determination block displays a character or a line drawing.
- the determination block displays a character or a line drawing.
- An orthogonal transform unit 105 that outputs a residual coefficient.
- the specific region determination unit 103 determines that the determination block is a specific region
- the orthogonal transform unit 105 is always set to a block size of 4 ⁇ 4 pixels. For each transform processing unit, the orthogonal transform of the determination block is selectively performed.
- orthogonal transformation is always performed with a size of 4 ⁇ 4 pixels, and in the determination block determined not to be the specific area, a plurality of predetermined TU sizes are determined. Orthogonal transformation is performed with a TU size selected from among them.
- the specific region has many high-frequency components, it is a region where noise is likely to occur due to quantization. However, since the generated noise is suppressed to a small size of 4 ⁇ 4 pixels, subjective image quality can be improved.
- the determination block is a specific area
- 4 ⁇ 4 pixels are always uniquely determined as the TU size of the determination block, so that the processing required to determine the TU size can be omitted, The amount of processing can be reduced.
- the TU size can be uniquely determined in the specific area, so that the amount of calculation processing can be reduced.
- FIG. 3 is a block diagram of image coding apparatus 200 according to the present embodiment.
- the image coding apparatus 200 divides an image input in units of pictures into blocks and performs a coding process in units of blocks to generate a code string. Note that the second embodiment will be described with a focus on differences from the first embodiment, and the description of the same configuration may be omitted.
- the image coding apparatus 200 is different from the image coding apparatus 100 illustrated in FIG. 1 in that the specific area determination unit 103 and the orthogonal transform unit 105 are replaced with a specific area determination unit. The difference is that the unit 203 and the orthogonal transform unit 205 are provided.
- the specific area determination unit 203 outputs, to the orthogonal transform unit 205, a result of determining whether or not the determination block is a specific area in addition to the operation shown in the first embodiment.
- the orthogonal transform unit 205 When the specific region determination unit 203 determines that the determination block is not a specific region, the orthogonal transform unit 205 always executes orthogonal conversion of the determination block. Specifically, the orthogonal transform unit 205 receives the determination result from the specific region determination unit 203 and determines whether or not to perform orthogonal transform based on the received determination result.
- whether or not to perform orthogonal transformation can be selected only when the TU size is 4 ⁇ 4 pixels.
- the specific area determination unit 203 determines that the determination block is not the specific area, even if a 4 ⁇ 4 pixel block is selected as the TU size, the orthogonal transform unit 205 always performs orthogonal transformation.
- the orthogonal transform unit 205 can selectively execute orthogonal transform.
- FIG. 4 is a flowchart showing determination of a specific area and orthogonal transformation processing according to the present embodiment.
- the orthogonal transform unit 205 selectively performs orthogonal transform on the determination block for each 4 ⁇ 4 pixel block (S140).
- the orthogonal transformation unit 205 selects execution of orthogonal transformation.
- the orthogonal transform unit 205 selects not to perform orthogonal transform when the difference between the reconstructed image obtained when not performing orthogonal transform and the input image is smaller than when performing orthogonal transform.
- the orthogonal transform unit 205 selectively performs orthogonal transform in the same manner as in the first embodiment.
- the orthogonal transform unit 205 always performs orthogonal transform with the selected TU size (S250).
- the orthogonal transform unit 205 can normally select whether to perform orthogonal transform. However, determining whether or not to perform orthogonal transformation in all 4 ⁇ 4 pixel blocks requires a large amount of calculation processing.
- the orthogonal transform unit 205 always performs orthogonal transform even when it is determined that the determination block is not a specific region, even if a TU size of 4 ⁇ 4 pixels is selected. To do. Thereby, the amount of calculation processing required to determine whether or not to perform orthogonal transform can be reduced.
- the determination block determined not to be a specific area is an area that does not include characters or line drawings, such as a natural image. For this reason, even if a high frequency component is lost by orthogonal transformation and quantization, it is not conspicuous subjectively. That is, subjective image quality does not deteriorate.
- the area determined to be a specific area is an area including characters or line drawings, as described above, when high frequency components are lost, noise is noticeable and subjective image quality deteriorates. There is a case. For this reason, when the subjective image quality is better when the orthogonal transform is not performed, the subjective image quality can be improved by selecting the orthogonal transform unit 205 not to perform the orthogonal transform.
- the TU size of the determination block can always be uniquely set as a 4 ⁇ 4 pixel block by the specific region determination unit 203 and the orthogonal transform unit 205. Furthermore, it can be operated by switching whether or not to perform orthogonal transform only on a specific region.
- HEVC can switch whether or not to perform orthogonal transformation in a 4 ⁇ 4 pixel block, which is effective in improving image quality.
- the amount of processing increases significantly.
- the frequency component spreads without concentrating on the specific component. Therefore, encoding efficiency can be improved by always performing orthogonal transform.
- orthogonal transform section 205 always performs orthogonal transform of a determination block when it is determined by specific area determination section 203 that the determination block is not a specific area.
- orthogonal transformation is always executed when it is determined that the region is not a specific region, so that it is possible to reduce the amount of processing required to determine whether or not to perform orthogonal transformation.
- orthogonal transformation can be selectively performed so that the subjective image quality is improved. In this way, whether or not to perform orthogonal transform can be switched adaptively only when necessary, so that it is possible to realize improvement in subjective image quality and improvement in coding efficiency while suppressing the amount of calculation processing.
- FIG. 5 is a flowchart illustrating specific area determination and orthogonal transform processing according to a modification of the present embodiment.
- the orthogonal transform unit 205 always performs orthogonal transform of the determination block for each set transform processing unit (S250). That is, regardless of the determination result of the specific area determination unit 203, the orthogonal transform unit 205 may always execute the orthogonal transform. In other words, regardless of whether or not the determination block is a specific region, the orthogonal transform unit 205 may always perform orthogonal transform.
- the orthogonal transform unit 205 always has 4 ⁇ 4 pixels when the specific region determination unit 203 determines that the determination block is a specific region.
- the orthogonal transform of the determination block is always executed for each transform processing unit set to the block size.
- Embodiment 3 will be described with reference to FIGS.
- FIG. 6 is a block diagram of an image coding apparatus 300 according to the present embodiment.
- the image encoding device 300 divides an image input in units of pictures into blocks, and performs an encoding process in units of blocks to generate a code string.
- Note that the third embodiment will be described with a focus on differences from the first embodiment, and the description of the same configuration may be omitted.
- the image coding apparatus 300 includes a specific area determination unit 303 instead of the specific area determination unit 103 as compared to the image coding apparatus 100 illustrated in FIG. 1.
- the difference is that a quantization parameter setting unit 312 is newly provided.
- the specific area determination unit 303 outputs the result of determining whether or not the determination block is a specific area to the quantization parameter setting unit 312 in addition to the operation described in the first embodiment.
- the quantization parameter setting unit 312 sets a quantization parameter used by the quantization unit 106 using the determination result output from the specific region determination unit 303.
- the quantization parameter setting unit 312 sets a quantization parameter in a predetermined processing unit based on a predetermined criterion. For example, the quantization parameter setting unit 312 sets the quantization parameter in a predetermined processing unit based on rate control or the like. Specifically, the quantization parameter setting unit 312 sets the quantization parameter so that the generated code string approaches a predetermined bit rate.
- the predetermined processing unit is a processing unit in which the quantization parameter can be changed.
- the predetermined processing unit is a determination block.
- the quantization parameter setting unit 312 resets the set quantization parameter to a larger value when the determination block is a specific region. In other words, when the determination block is a specific region, the quantization parameter setting unit 312 sets Q1 that is larger than the quantization parameter value Q2 set when it is determined that the determination block is not the specific region, Set the quantization parameter.
- the quantization parameter setting unit 312 outputs the set quantization parameter to the quantization unit 106.
- the quantization unit 106 quantizes the residual coefficient signal input from the orthogonal transform unit 105 in units of TUs. At this time, the quantization unit 106 generates a quantization residual coefficient signal by performing quantization using the quantization value (quantization parameter) set by the quantization parameter setting unit 312 and the quantization matrix. . Details of the quantization unit 106 will be described later.
- the inverse quantization unit 107 applies the quantization value (quantization value) used when the quantization residual coefficient signal input from the quantization unit 106 is quantized by the quantization unit 106 to the quantization residual coefficient signal.
- the quantization residual coefficient signal is output to the inverse orthogonal transform unit 108 by performing inverse quantization using the quantization parameter) and the quantization matrix.
- FIG. 7 is a flowchart showing specific area determination, orthogonal transform processing, and quantization parameter setting according to the present embodiment.
- the quantization parameter setting unit 312 sets the quantization parameter to Q1 (S360).
- the quantization parameter setting unit 312 sets the quantization parameter to Q2 (S370).
- Quantization parameters are set for each determination block, for example.
- the quantization parameter setting unit 312 sets the quantization parameter according to whether or not the determination block is a specific region. For example, when the determination block is a specific region, the quantization parameter used for quantization of the determination block is set to Q1, and when the determination block is not the specific region, the quantization parameter used for quantization of the determination block is set to Q2.
- Q1 is set to a value equal to or greater than Q2.
- Q2 is a value set when it is not determined to be a specific area, and is a value determined based on rate control or the like.
- the quantization parameter setting unit 312 sets Q1 that is larger than Q2 as a quantization parameter by adding an offset to Q2 determined based on rate control or the like. Thereby, the determination block determined to be the specific region can be roughly quantized.
- the TU size is always set to 4 ⁇ 4 pixels.
- the quantization parameter for the specific region is a value larger than the quantization parameter for the region that is not the specific region, it is possible to suppress an increase in the code amount.
- the specific area is a small block with a TU size of 4 ⁇ 4 pixels, the prediction direction is easy to hit and the prediction accuracy is high.
- the TU is a simple block image because the TU size is a small block size of 4 ⁇ 4 pixels. For this reason, since prediction accuracy becomes high and a residual component can be reduced, even if it coarsely quantizes, an image quality does not deteriorate easily.
- the size of the predetermined processing unit that is the processing unit for setting the quantization parameter may be any standard.
- the predetermined processing unit may be composed of a plurality of determination blocks.
- the predetermined processing unit may be a CU.
- the predetermined processing unit includes at least one determination block. That is, the predetermined processing unit is larger than the size of the determination block.
- the quantization parameter setting unit 312 sets the quantization parameter based on the ratio of the determination blocks determined to be a specific area within a predetermined processing unit. Specifically, the quantization parameter setting unit 312 is determined based on a predetermined criterion when the ratio of the determination block determined as a specific region within a predetermined processing unit is larger than a predetermined threshold. Set the quantization value to a larger value.
- the size of a predetermined processing unit is 32 ⁇ 32 pixels, and 16 8 ⁇ 8 pixel determination blocks are included therein.
- the quantization parameter setting unit 312 has 7 or less determination blocks determined to be the specific region. Then, the quantization parameter is increased as compared with the case where it is determined.
- FIG. 8 is a flowchart showing the setting of the quantization parameter according to the present embodiment.
- the quantization parameter setting unit 312 sets the quantization parameter to Q2 based on a predetermined criterion (S361). For example, the quantization parameter setting unit 312 determines the quantization parameter based on rate control or the like.
- the quantization parameter setting unit 312 determines whether or not the ratio of the determination block determined as the specific area within the predetermined processing unit is larger than a predetermined threshold (S362).
- the quantization parameter setting unit 312 sets Q1 that is a value larger than Q2 as a quantization parameter by adding an offset to Q2. (S363).
- the quantization parameter setting unit 312 outputs the quantization parameter set in Q2 to the quantization unit 106 as it is.
- the quantization parameter setting unit 312 uses the case where the ratio of the determination blocks determined as the specific area is equal to or less than the threshold as the quantization parameter when the ratio of the determination blocks determined as the specific area is larger than the threshold. Set a value larger than the quantization parameter.
- [Summary] Image coding apparatus 300 sets a quantization parameter of a determination block that is determined to be a specific region by specific region determination unit 303 when it is determined that the determination block is not a specific region.
- the quantization parameter of the determination block determined to be the specific region is set to a value larger than the quantization parameter set when the determination block is determined not to be the specific region.
- the amount of codes can be reduced.
- the determination block determined as the specific area is selected as a TU size of 4 ⁇ 4 pixels, that is, a small block, deterioration in image quality is not conspicuous. Therefore, it is possible to suppress deterioration of the subjective image quality of the specific area and reduce the code amount.
- image coding apparatus 300 is a specific region in a predetermined processing unit when a predetermined processing unit that is a processing unit for setting a quantization value is equal to or larger than the size of the determination block.
- the quantization parameter when the ratio of the determination block determined to be greater than a predetermined threshold is greater than the quantization parameter when the ratio of the determination block determined as a specific area within a predetermined processing unit is equal to or less than the threshold.
- the quantization parameter of the region having a large ratio of the specific region is set to a larger value than the quantization parameter of the region having a small ratio of the specific region, so that the code amount of the region having a large ratio of the specific region can be reduced.
- the fourth embodiment is an embodiment in which the second embodiment and the third embodiment described above are combined.
- FIG. 9 is a block diagram of an image encoding device 400 according to a modification of the embodiment.
- the image coding apparatus 400 divides an image input in units of pictures into blocks, and performs a coding process in units of blocks to generate a code string.
- differences from the second and third embodiments will be mainly described, and the description of the same configuration may be omitted.
- image coding apparatus 400 differs from image coding apparatus 300 according to Embodiment 3 shown in FIG. 6 in that it includes orthogonal transform section 205 instead of orthogonal transform section 105. Yes.
- the orthogonal transform unit 205 has the same configuration as the orthogonal transform unit 205 according to the second embodiment.
- FIG. 10 is a flowchart illustrating specific area determination, orthogonal transform processing, and quantization parameter setting according to a modification of the embodiment.
- orthogonal transform is selected for each block of 4 ⁇ 4 pixels selected as a TU size for a determination block determined to be a specific region. Is executed automatically. Further, the quantization parameter used for quantization of the determination block determined to be the specific region is set to Q1 which is a value larger than the quantization parameter value Q2 set when it is determined that the determination block is not the specific region.
- the residual coefficient to be quantized is a value in the spatial domain, not the frequency domain.
- the residual coefficient indicates a difference in luminance value. Since quantization is performed in the spatial domain, the effect of losing high-frequency components does not appear and image quality deterioration can be suppressed.
- the specific area is an area including a character or a line drawing
- the accuracy of intra prediction is better than that of a natural image, and the residual coefficient often has a small value.
- the code amount of one TU can be reduced, and the code amount as a whole can also be suppressed.
- the quantization parameter for the determination block determined as the specific region is increased, the code amount of one TU can be further reduced.
- the TU size is a small block of 4 ⁇ 4 pixels
- the prediction direction is easy to hit and the prediction accuracy is high.
- the TU is a small block size of 4 ⁇ 4 pixels. Increases accuracy.
- orthogonal transformation is always executed in a determination block that is determined not to be a specific region.
- the determination block determined not to be the specific region is a complex image such as a natural image. For this reason, even if high frequency components are lost due to orthogonal transformation and quantization, subjective deterioration of image quality is suppressed. Therefore, it is possible to reduce the processing amount required to determine whether or not to perform orthogonal transformation without degrading subjective image quality.
- the image coding apparatus 400 According to the present embodiment, it is possible to improve the subjective image quality and reduce the amount of calculation processing.
- FIG. 11 is a flowchart illustrating specific area determination and orthogonal transform processing according to a modification of the present embodiment.
- the orthogonal transform unit 205 always performs orthogonal transform of the determination block for each set transform processing unit (S250). That is, regardless of the determination result of the specific area determination unit 203, the orthogonal transform unit 205 may always execute the orthogonal transform. In other words, regardless of whether or not the determination block is a specific region, the orthogonal transform unit 205 may always perform orthogonal transform.
- Embodiments 1 to 4 have been described as examples of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can also be applied to an embodiment in which changes, replacements, additions, omissions, and the like are appropriately performed. In addition, it is possible to combine the components described in the first to fourth embodiments to form a new embodiment.
- the orthogonal transform unit 205 determines the determination block for each set transform processing unit regardless of whether the determination block is a specific region.
- orthogonal transformation may be selectively executed. Even in this case, if it is determined that the determination block is a specific area, the processing required to determine whether or not to perform orthogonal transformation can be reduced, so that the amount of calculation processing can be reduced. it can.
- the HEVC standard has been described as the encoding standard used by the image encoding apparatus according to each embodiment.
- the encoding standard only needs to selectively perform orthogonal transformation. Therefore, the encoding standard is not limited to the HEVC standard.
- the processing described in the above embodiment is performed by recording a program having a function equivalent to each unit included in the image encoding device described in the above embodiment on a recording medium such as a flexible disk.
- a recording medium such as a flexible disk.
- the recording medium is not limited to a flexible disk, but can be similarly implemented as long as it can record a program, such as an optical disk, an IC card, and a ROM (Read Only Memory) cassette.
- a function equivalent to each unit included in the image encoding device shown in the above embodiment may be realized as an LSI which is an integrated circuit. These may be integrated into one chip so as to include a part or all of them.
- An LSI may also be called an IC, a system LSI, a super LSI, or an ultra LSI depending on the degree of integration.
- the method of circuit integration is not limited to LSI, and implementation with a dedicated circuit or a general-purpose processor is also possible.
- An FPGA Field Programmable Gate Array
- a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.
- each component (the picture memory 101, the block division unit 102, the specific area determination units 103, 203, and 303, and the difference included in the image encoding devices 100, 200, 300, and 400 according to the present disclosure
- Operation unit 104, orthogonal transform units 105 and 205, quantization unit 106, inverse quantization unit 107, inverse orthogonal transform unit 108, addition operation unit 109, predicted image generation unit 110, and code string generation unit 111 and a quantization parameter setting unit 312) are programs executed on a computer including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM, a communication interface, an I / O port, a hard disk, a display, and the like. It may be realized by software such as It may be implemented in hardware such as circuit.
- the present disclosure is useful, for example, for an image encoding device that inputs a paper such as a newspaper or a magazine as image data of a still image and outputs it as a still image code string by performing an encoding process.
- the present invention is useful as an image encoding device that inputs video in which characters or figures are multiplexed as moving image data and outputs it as a moving image code string by performing encoding processing.
- Image coding apparatus 101 Picture memory 102 Block division unit 103, 203, 303 Specific area determination unit 104 Difference calculation unit 105, 205 Orthogonal transformation unit 106 Quantization unit 107 Inverse quantization unit 108 Inverse orthogonal transformation Unit 109 addition calculation unit 110 prediction image generation unit 111 code string generation unit 312 quantization parameter setting unit
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Abstract
Provided is an image coding device (100) for coding an inputted image, comprising: a specified region determination unit (103) which determines, for each determination block which is formed from a plurality of pixels and which is included in the inputted image, whether the determination block is a specified region which includes a text character or line art; and an orthogonal transform unit (105) which, by selectively carrying out, on a transform processing unit which is adaptively selected from a plurality of transform processing units, an orthogonal transform of the determination block, outputs a residual coefficient. When it is determined by the specified region determination unit (103) that the determination block is the specified region, the orthogonal transform unit (105) selectively carries out, on each of the transform processing units which are consistently set to a 4×4-pixel block size, the orthogonal transform of the determination block.
Description
本開示は、符号化動作における直交変換を選択的に行うことができる画像符号化装置に関する。
The present disclosure relates to an image encoding device that can selectively perform orthogonal transform in an encoding operation.
近年、マルチメディアアプリケーションの発展に伴い、画像、音声及びテキストなど、あらゆるメディアの情報を統一的に扱うことが一般的になってきた。また、ディジタル化された画像は膨大なデータ量を持つため、蓄積及び伝送のためには、画像の情報圧縮技術が不可欠である。
In recent years, with the development of multimedia applications, it has become common to handle all media information such as images, sounds and texts in a unified manner. Also, since a digitized image has a huge amount of data, an image information compression technique is indispensable for storage and transmission.
一方で、圧縮した画像データを相互運用するためには、圧縮技術の標準化も重要である。例えば、画像圧縮技術の標準規格としては、ITU-T(国際電気通信連合 電気通信標準化部門)のH.261、H.263、H.264、及び、ISO/IEC(国際標準化機構)のMPEG-1、MPEG-3、MPEG-4、MPEG-4AVCなどがある。また、現在は、ITU-TとISO/IECとの共同によるHEVC(High Efficiency Video Coding)と呼ばれる次世代画像符号化方式の標準化活動が進んでいる。
On the other hand, standardization of compression technology is also important for interoperating compressed image data. For example, as a standard for image compression technology, H.264 of ITU-T (International Telecommunication Union, Telecommunication Standardization Division). 261, H.H. 263, H.M. H.264 and ISO / IEC (International Organization for Standardization) MPEG-1, MPEG-3, MPEG-4, MPEG-4AVC, and the like. At present, standardization activities for a next-generation image coding method called HEVC (High Efficiency Video Coding) in cooperation with ITU-T and ISO / IEC are in progress.
このような画像の符号化では、符号化対象の各ピクチャを符号化単位ブロックに分割し、ブロック毎に時間方向及び空間方向の冗長性を削減することによって情報量の圧縮を行う。時間的な冗長性の削減を目的とする画面間予測符号化では、前方又は後方のピクチャを参照してブロック単位で動きの検出及び予測画像の作成を行い、得られた予測画像と符号化対象のブロックとの差分画像を取得する。また、空間的な冗長性の削減を目的とする画面内予測符号化では、周辺の符号化済みブロックの画素情報から予測画像の生成を行い、得られた予測画像と符号化対象のブロックとの差分画像を取得する。
In such image coding, each picture to be coded is divided into coding unit blocks, and the amount of information is compressed by reducing redundancy in the time direction and the space direction for each block. In inter-frame predictive coding for the purpose of reducing temporal redundancy, motion is detected and a predicted image is created in block units with reference to the front or rear picture, and the obtained predicted image and encoding target are obtained. The difference image with the block of is acquired. In addition, in the intra prediction encoding for the purpose of reducing spatial redundancy, a prediction image is generated from pixel information of surrounding encoded blocks, and the obtained prediction image and the block to be encoded are Get the difference image.
得られた差分画像に対して離散コサイン変換等の直交変換及び量子化を行う。直交変換では、輝度成分情報及び色差成分情報を周波数成分情報に変換する。一般的に、周波数成分が高いほど、人間の目で認識しにくい情報となる。そのため、通常、量子化では高周波数領域ほど量子化の幅を粗くし、人間の目で認識しにくい情報を省略し、人間の目で劣化が分かりにくいように符号化が行われる。さらに、可変長符号化を用いて符号列を生成することで情報量が圧縮される。
* Perform orthogonal transform such as discrete cosine transform and quantization on the obtained difference image. In orthogonal transform, luminance component information and color difference component information are converted into frequency component information. In general, the higher the frequency component, the more difficult it is for human eyes to recognize. For this reason, in general, quantization is performed such that the higher the frequency region is, the wider the quantization range is, the information that is difficult to be recognized by the human eye is omitted, and the deterioration is difficult to understand by the human eye. Furthermore, the amount of information is compressed by generating a code string using variable length coding.
HEVC(非特許文献1参照)では、前述の直交変換において、直交変換対象のブロックサイズが、4×4画素、8×8画素、16×16画素、32×32画素の4候補がある。ブロックサイズを決定する際には、符号化対象のブロック毎に、四分木構造で分割できる範囲の中で、4候補の中からコスト判定によっていずれか1つのブロックサイズを選択する。
In HEVC (see Non-Patent Document 1), in the above-described orthogonal transform, there are four candidates for the block size to be orthogonally transformed: 4 × 4 pixels, 8 × 8 pixels, 16 × 16 pixels, and 32 × 32 pixels. When determining the block size, one block size is selected from among four candidates by cost determination within a range that can be divided by the quadtree structure for each block to be encoded.
これにより、画像の性質に応じて直交変換のサイズを適応的に切り替えることで符号化効率の向上に大きく貢献している。また、4×4画素のサイズを選択した場合に限り、直交変換を行わずに差分画像をそのまま量子化するという方法を選択することも可能となっている。
This contributes greatly to the improvement of coding efficiency by adaptively switching the size of orthogonal transform according to the nature of the image. Also, only when a size of 4 × 4 pixels is selected, it is possible to select a method of quantizing a difference image as it is without performing orthogonal transformation.
また、前述の量子化処理では、ブロック毎に設定した量子化パラメータと、ピクチャ毎に設定した量子化行列とを掛け合わせることで決定される量子化幅によって量子化が行われる。
In the above-described quantization process, quantization is performed with a quantization width determined by multiplying the quantization parameter set for each block and the quantization matrix set for each picture.
HEVCでは、前述の通り、直交変換のブロックサイズが4種類あり、分割方法も複雑なため、いずれか1つのサイズを選ぼうとすると、直交変換に要する演算処理量がH.264に比べ多くなる。
In HEVC, as described above, there are four types of block sizes for orthogonal transformation and the division method is complicated. Therefore, when one of the sizes is selected, the amount of calculation processing required for orthogonal transformation is H.264. More than H.264.
また、単に演算処理量を低減するために、直交変換対象のブロックを一意に定めた場合、画像の種類によっては、直交変換及び量子化により発生したノイズによって主観的な画質が低下する恐れもある。
In addition, when the orthogonal transformation target block is uniquely determined in order to simply reduce the calculation processing amount, depending on the type of image, there is a risk that subjective image quality may be deteriorated due to noise generated by the orthogonal transformation and quantization. .
そこで、本開示は、主観画質を向上させ、かつ、演算処理量を削減することができる画像符号化装置及び画像符号化方法を提供する。
Therefore, the present disclosure provides an image encoding device and an image encoding method capable of improving subjective image quality and reducing the amount of calculation processing.
本開示に係る画像符号化装置は、入力画像を符号化する画像符号化装置であって、入力画像に含まれる複数の画素からなる判定ブロック毎に、当該判定ブロックが文字又は線画を含む特定領域であるか否かを判定する判定部と、複数の変換処理単位の中から適応的に選択された変換処理単位で、判定ブロックの直交変換を選択的に行うことで、残差係数を出力する直交変換部とを備え、直交変換部は、判定部によって判定ブロックが特定領域であると判定された場合、常に4×4画素のブロックサイズに設定された変換処理単位毎に、判定ブロックの直交変換を選択的に行う。
An image encoding device according to the present disclosure is an image encoding device that encodes an input image, and for each determination block including a plurality of pixels included in the input image, the determination block includes a specific area including a character or a line drawing A residual coefficient is output by selectively performing orthogonal transform of the determination block in a determination unit that determines whether or not and a transform processing unit adaptively selected from a plurality of transform processing units. An orthogonal transform unit, and when the determination unit determines that the determination block is a specific area, the orthogonal transform unit always orthogonalizes the determination block for each conversion processing unit set to a block size of 4 × 4 pixels. Perform the conversion selectively.
本開示に係る画像符号化装置によれば、主観画質を向上させ、かつ、演算処理量を削減することができる。
According to the image coding apparatus according to the present disclosure, it is possible to improve the subjective image quality and reduce the amount of calculation processing.
以下、適宜図面を参照しながら、実施の形態を詳細に説明する。ただし、必要以上に詳細な説明は省略する場合がある。例えば、既によく知られた事項の詳細説明や実質的に同一の構成に対する重複説明を省略する場合がある。これは、以下の説明が不必要に冗長になるのを避け、当業者の理解を容易にするためである。
Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed explanation than necessary may be omitted. For example, detailed descriptions of already well-known matters and repeated descriptions for substantially the same configuration may be omitted. This is to avoid the following description from becoming unnecessarily redundant and to facilitate understanding by those skilled in the art.
なお、発明者らは、当業者が本開示を十分に理解するために添付図面及び以下の説明を提供するのであって、これらによって請求の範囲に記載の主題を限定することを意図するものではない。
In addition, the inventors provide the accompanying drawings and the following description in order for those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims. Absent.
(実施の形態1)
以下、図1及び図2を用いて、実施の形態1を説明する。 (Embodiment 1)
Hereinafter, the first embodiment will be described with reference to FIGS. 1 and 2.
以下、図1及び図2を用いて、実施の形態1を説明する。 (Embodiment 1)
Hereinafter, the first embodiment will be described with reference to FIGS. 1 and 2.
[画像符号化装置全体の処理説明]
図1は、本実施の形態に係る画像符号化装置100のブロック図である。画像符号化装置100は、ピクチャ単位で入力された画像をブロックに分割し、ブロック単位で符号化処理を行うことで、符号列を生成する。 [Description of Processing of Entire Image Encoding Device]
FIG. 1 is a block diagram of animage coding apparatus 100 according to the present embodiment. The image encoding apparatus 100 divides an image input in units of pictures into blocks and performs an encoding process in units of blocks to generate a code string.
図1は、本実施の形態に係る画像符号化装置100のブロック図である。画像符号化装置100は、ピクチャ単位で入力された画像をブロックに分割し、ブロック単位で符号化処理を行うことで、符号列を生成する。 [Description of Processing of Entire Image Encoding Device]
FIG. 1 is a block diagram of an
図1に示すように、画像符号化装置100は、ピクチャメモリ101と、ブロック分割部102と、特定領域判定部103と、差分演算部104と、直交変換部105と、量子化部106と、逆量子化部107と、逆直交変換部108と、加算演算部109と、予測画像生成部110と、符号列生成部111とを備える。
As illustrated in FIG. 1, the image encoding device 100 includes a picture memory 101, a block division unit 102, a specific area determination unit 103, a difference calculation unit 104, an orthogonal transformation unit 105, a quantization unit 106, An inverse quantization unit 107, an inverse orthogonal transform unit 108, an addition operation unit 109, a predicted image generation unit 110, and a code string generation unit 111 are provided.
ピクチャメモリ101は、入力画像信号をピクチャ単位で格納する。ピクチャメモリ101は、ブロック分割部102からの読出し命令を受け付けた場合に、当該読出し命令に係る画像信号を出力する。
The picture memory 101 stores the input image signal in units of pictures. When the picture memory 101 receives a read command from the block division unit 102, the picture memory 101 outputs an image signal related to the read command.
なお、入力画像信号は、例えば、新聞又は雑誌などの紙面の静止画を示す画像データである。あるいは、入力画像信号は、文字又は線画が多重化された映像、例えば、字幕を含む映像を示す動画像データでもよい。
The input image signal is image data indicating a still image on a paper surface such as a newspaper or a magazine. Alternatively, the input image signal may be moving image data indicating a video in which characters or line drawings are multiplexed, for example, a video including subtitles.
ブロック分割部102は、ピクチャメモリ101から入力された画像信号を、符号化処理単位であるコーディングユニット(CU)と呼ばれる、例えば、64×64画素のブロックに分割する。
The block dividing unit 102 divides the image signal input from the picture memory 101 into blocks of, for example, 64 × 64 pixels called a coding unit (CU) that is an encoding processing unit.
ブロック分割部102は、さらに、CUを予測画像生成の処理単位であるプレディクションユニット(PU)と呼ばれる、例えば、8×8画素のブロックに分割する。
The block dividing unit 102 further divides the CU into, for example, 8 × 8 pixel blocks called prediction units (PUs) that are processing units for predictive image generation.
上記においてCUは、64×64画素のブロックを説明したが、32×32画素、16×16画素、8×8画素のブロックサイズでも構わない。
In the above description, the CU describes a block of 64 × 64 pixels, but a block size of 32 × 32 pixels, 16 × 16 pixels, or 8 × 8 pixels may be used.
上記においてPUは、8×8画素のブロックを説明したが、例えば8×16画素、8×4画素などの別のサイズでも構わない。なお、PUは、CUのブロックサイズと同じサイズ、又は、CUを2分割若しくは4分割したサイズとなる。
In the above description, the PU has been described as an 8 × 8 pixel block. However, for example, another size such as 8 × 16 pixels or 8 × 4 pixels may be used. The PU has the same size as the block size of the CU, or a size obtained by dividing the CU into two or four.
特定領域判定部103は、入力画像に含まれる複数の画素からなる判定ブロック毎に、当該判定ブロックが文字又は線画を含む特定領域であるか否かを判定する。具体的には、特定領域判定部103は、ブロック分割部102から出力された符号化対象ピクチャから画像特徴量を取得し、予め定められる判定ブロック毎に特定領域であるか否かを判定する。
The specific area determination unit 103 determines, for each determination block including a plurality of pixels included in the input image, whether or not the determination block is a specific area including a character or a line drawing. Specifically, the specific area determination unit 103 acquires an image feature amount from the encoding target picture output from the block division unit 102 and determines whether or not the predetermined area is a specific area for each predetermined determination block.
なお、特定領域とは、文字又は線画を含む領域をいう。文字又は線画で描画された領域には、文字又は線画と背景画像との間にエッジが発生しやすい。したがって、特定領域は、エッジを含む領域でもある。
It should be noted that the specific area refers to an area including characters or line drawings. In an area drawn with a character or line drawing, an edge is likely to occur between the character or line drawing and the background image. Therefore, the specific area is also an area including an edge.
特定領域と判定された判定ブロックは、直交変換の処理単位であるトランスフォームユニット(TU)と呼ばれるブロックのサイズ(TUサイズ)として、常に4×4画素が選択される。TUサイズは、32×32画素、16×16画素、8×8画素、4×4画素のブロックがある。特定領域でないと判断された判定ブロックのTUサイズは、上記の32×32画素~4×4画素のブロックのうち、直交変換及び量子化などの符号化効率が高くなる1つが選ばれる。
For the determination block determined as the specific area, 4 × 4 pixels are always selected as a block size (TU size) called a transform unit (TU) that is a unit of orthogonal transformation. The TU size includes blocks of 32 × 32 pixels, 16 × 16 pixels, 8 × 8 pixels, and 4 × 4 pixels. The TU size of the determination block determined not to be the specific region is selected from the above blocks of 32 × 32 pixels to 4 × 4 pixels, which has high encoding efficiency such as orthogonal transform and quantization.
なお、TUは、CUのブロックサイズと同じサイズか、それよりも小さいブロックサイズとなる。また、以降の処理は、処理内容に応じて、CU、PU、TUのいずれかのブロック単位で処理が行われるものとする。
Note that the TU has the same size as the CU block size or a smaller block size. The subsequent processing is performed in units of blocks of CU, PU, and TU depending on the processing content.
特定領域の判定の詳細については、後述する。
Details of the specific area determination will be described later.
差分演算部104は、特定領域判定部103から入力されたPU単位の画像信号と、予測画像生成部110から入力されたPU単位の予測画像信号との差分値である差分画像信号を生成する。差分演算部104は、生成した差分画像信号を直交変換部105に出力する。
The difference calculation unit 104 generates a difference image signal that is a difference value between the PU unit image signal input from the specific region determination unit 103 and the PU unit prediction image signal input from the prediction image generation unit 110. The difference calculation unit 104 outputs the generated difference image signal to the orthogonal transformation unit 105.
直交変換部105は、複数の変換処理単位の中から適応的に選択された変換処理単位で、判定ブロックの直交変換を選択的に行うことで、残差係数信号を出力する。具体的には、直交変換部105は、差分演算部104から入力される差分画像信号に、TU単位で直交変換を行うことで、残差係数信号を生成する。
The orthogonal transform unit 105 outputs a residual coefficient signal by selectively performing orthogonal transform of the determination block in a transform processing unit adaptively selected from a plurality of transform processing units. Specifically, the orthogonal transform unit 105 generates a residual coefficient signal by performing orthogonal transform on the difference image signal input from the difference calculation unit 104 in units of TUs.
なお、直交変換部105は、変換処理単位(TU)が4×4画素の場合に、直交変換を行うか否かを選択可能である。つまり、直交変換部105は、TUサイズが4×4画素の場合、直交変換を選択的に行う。
Note that the orthogonal transform unit 105 can select whether or not to perform orthogonal transform when the transform processing unit (TU) is 4 × 4 pixels. That is, the orthogonal transform unit 105 selectively performs orthogonal transform when the TU size is 4 × 4 pixels.
例えば、直交変換部105は、TUサイズが4×4画素の場合、差分画像信号に直交変換を行うことで、残差係数信号を生成して出力することができる(動作A)。あるいは、直交変換部105は、TUサイズが4×4画素の場合、差分画像信号に直交変換を行うことなく、差分画像信号をそのまま残差係数信号として出力することもできる(動作B)。直交変換部105は、例えば、所定のコスト判定に基づいて、動作A及び動作Bのうち符号化効率の優れた方を選択する。
For example, when the TU size is 4 × 4 pixels, the orthogonal transform unit 105 can generate and output a residual coefficient signal by performing orthogonal transform on the difference image signal (operation A). Alternatively, when the TU size is 4 × 4 pixels, the orthogonal transform unit 105 can output the difference image signal as a residual coefficient signal without performing orthogonal transform on the difference image signal (operation B). For example, the orthogonal transform unit 105 selects one of the operation A and the operation B that has better coding efficiency based on a predetermined cost determination.
直交変換部105は、特定領域判定部103によって判定ブロックが特定領域であると判定された場合、常に4×4画素のブロックサイズに設定された変換処理単位(TU)毎に、判定ブロックの直交変換を選択的に行うことで、残差係数を出力する。すなわち、直交変換部105は、判定ブロックに含まれるTU毎に、直交変換を行うか否かを判定する。直交変換部105は、TU毎に、(i)直交変換を行う場合は、差分画像信号を直交変換することで残差係数信号を生成して出力し、(ii)直交変換を行わない場合は、差分画像信号をそのまま残差係数信号として出力する。
When the specific region determination unit 103 determines that the determination block is a specific region, the orthogonal transform unit 105 always orthogonalizes the determination block for each transform processing unit (TU) set to a block size of 4 × 4 pixels. Residual coefficients are output by selectively performing the transformation. That is, the orthogonal transform unit 105 determines whether or not to perform orthogonal transform for each TU included in the determination block. For each TU, the orthogonal transform unit 105 generates and outputs a residual coefficient signal by performing orthogonal transform on the difference image signal when performing (i) orthogonal transform, and (ii) when not performing orthogonal transform. The difference image signal is output as a residual coefficient signal as it is.
また、直交変換部105は、特定領域判定部103によって判定ブロックが特定領域ではないと判定された場合、予め定められた複数の変換処理単位(TU)から選択された変換処理単位で、判定ブロックの直交変換を選択的に行うことで、残差係数を出力する。具体的には、直交変換部105は、判定ブロックが特定領域ではないと判定された場合、32×32画素~4×4画素のブロックから1つのブロックを選択する。なお、4×4画素のブロックが変換処理単位として選択された場合、上述したように、直交変換部105は、直交変換を行うか否かを選択可能である。
Further, when the specific area determination unit 103 determines that the determination block is not the specific area, the orthogonal transform unit 105 uses the determination block in a conversion processing unit selected from a plurality of predetermined conversion processing units (TU). The residual coefficient is output by selectively performing the orthogonal transformation. Specifically, when it is determined that the determination block is not a specific region, the orthogonal transform unit 105 selects one block from blocks of 32 × 32 pixels to 4 × 4 pixels. Note that when a 4 × 4 pixel block is selected as a transform processing unit, the orthogonal transform unit 105 can select whether or not to perform orthogonal transform as described above.
量子化部106は、直交変換部105から入力される残差係数信号に、TU単位で量子化を行う。このとき、量子化部106は、CU単位で設定される量子化値(量子化パラメータ)及び量子化行列に従って、残差係数信号の量子化を行うことで、量子化残差係数信号を生成する。
The quantization unit 106 quantizes the residual coefficient signal input from the orthogonal transform unit 105 in units of TUs. At this time, the quantization unit 106 generates a quantized residual coefficient signal by quantizing the residual coefficient signal according to a quantization value (quantization parameter) and a quantization matrix set in units of CUs. .
逆量子化部107は、量子化部106から入力される量子化残差係数信号に、TU単位で逆量子化を行うことで、再構成残差係数信号を生成する。逆量子化部107は、生成した再構成残差係数信号を逆直交変換部108に出力する。
The inverse quantization unit 107 generates a reconstructed residual coefficient signal by performing inverse quantization on the quantized residual coefficient signal input from the quantization unit 106 in units of TUs. The inverse quantization unit 107 outputs the generated reconstructed residual coefficient signal to the inverse orthogonal transform unit 108.
逆直交変換部108は、逆量子化部107から入力される再構成残差係数信号に、TU単位で逆直交変換を行うことで、再構成差分画像信号を生成する。そして、逆直交変換部108は、生成した再構成差分画像信号を加算演算部109に出力する。
The inverse orthogonal transform unit 108 generates a reconstructed difference image signal by performing inverse orthogonal transform on the reconstructed residual coefficient signal input from the inverse quantization unit 107 in units of TUs. Then, the inverse orthogonal transform unit 108 outputs the generated reconstructed difference image signal to the addition operation unit 109.
なお、逆直交変換部108は、TUサイズが4×4画素の場合に、逆直交変換を行うか否かを選択可能である。具体的には、逆直交変換部108は、逆量子化部107から再構成残差係数信号が入力された場合、再構成残差係数信号が直交変換部105において直交変換したものである場合、再構成残差係数信号を逆直交変換することで、再構成差分画像信号を生成して出力する。また、逆直交変換部108は、再構成残差係数信号が直交変換部105において直交変換せずに得られたものである場合、再構成残差係数信号を逆直交変換せずにそのまま再構成差分画像信号として加算演算部109に出力する。
The inverse orthogonal transform unit 108 can select whether to perform inverse orthogonal transform when the TU size is 4 × 4 pixels. Specifically, when the reconstructed residual coefficient signal is input from the inverse quantization unit 107, the inverse orthogonal transform unit 108 is obtained by orthogonally transforming the reconstructed residual coefficient signal in the orthogonal transform unit 105. By performing inverse orthogonal transform on the reconstructed residual coefficient signal, a reconstructed differential image signal is generated and output. Further, when the reconstructed residual coefficient signal is obtained without performing orthogonal transform in the orthogonal transform unit 105, the inverse orthogonal transform unit 108 reconstructs the reconstructed residual coefficient signal as it is without performing inverse orthogonal transform. The difference image signal is output to the addition operation unit 109.
加算演算部109は、逆直交変換部108から入力される再構成差分画像信号と、予測画像生成部110から入力される予測画像信号とをPU単位で加算することにより、再構成画像信号を生成する。
The addition operation unit 109 generates a reconstructed image signal by adding the reconstructed difference image signal input from the inverse orthogonal transform unit 108 and the predicted image signal input from the predicted image generation unit 110 in units of PUs. To do.
予測画像生成部110は、特定領域判定部103から入力されたPU単位の画像信号に、加算演算部109から入力される再構成画像信号を用いて、PU単位で画面内予測(イントラ予測)又は画面間予測(インター予測)を行うことで、予測画像を生成する。予測画像生成部110は、画面間予測を用いる場合は、既に符号化済みの過去のピクチャの再構成画像信号を用いる。一方、予測画像生成部110は、画面内予測を用いる場合は、符号化対象のPUに隣接する既に符号化済みの同じピクチャの再構成画像信号を用いる。なお、画像符号化装置100に入力される入力画像が1枚のピクチャのみから構成される静止画である場合は、過去のピクチャが存在しないため、常に画面内予測のみが用いられる。
The predicted image generation unit 110 uses the reconstructed image signal input from the addition operation unit 109 to the PU unit image signal input from the specific region determination unit 103, and performs intra-screen prediction (intra prediction) or PU unit. A prediction image is generated by performing inter-screen prediction (inter prediction). When using inter-screen prediction, the predicted image generation unit 110 uses a reconstructed image signal of a past picture that has already been encoded. On the other hand, when using intra prediction, the prediction image generation unit 110 uses a reconstructed image signal of the same picture that has already been encoded and is adjacent to the PU to be encoded. Note that if the input image input to the image coding apparatus 100 is a still image composed of only one picture, there is no past picture, and therefore only intra prediction is always used.
符号列生成部111は、量子化部106から入力された量子化残差係数信号、量子化行列信号、及び、その他の復号化処理時に必要となる符号化情報信号に、可変長符号化及び算術符号化を行うことで、符号列を生成する。
The code string generation unit 111 performs variable-length coding and arithmetic on the quantized residual coefficient signal, the quantization matrix signal, and other encoded information signals necessary for decoding processing input from the quantization unit 106. A code string is generated by encoding.
[特定領域判定部及び直交変換部]
ここで、特定領域判定部103及び直交変換部105が行う処理について、図2を用いて具体的に説明する。図2は、本実施の形態に係る特定領域の判定と直交変換処理とを示すフローチャートである。 [Specific area determination unit and orthogonal transform unit]
Here, the processing performed by the specificarea determination unit 103 and the orthogonal transform unit 105 will be specifically described with reference to FIG. FIG. 2 is a flowchart showing determination of a specific region and orthogonal transformation processing according to the present embodiment.
ここで、特定領域判定部103及び直交変換部105が行う処理について、図2を用いて具体的に説明する。図2は、本実施の形態に係る特定領域の判定と直交変換処理とを示すフローチャートである。 [Specific area determination unit and orthogonal transform unit]
Here, the processing performed by the specific
まず、特定領域判定部103は、入力画像に含まれる複数の画素からなる判定ブロック毎に、当該判定ブロックが文字又は線画を含む特定領域であるか否かを判定する(S110)。具体的には、特定領域判定部103は、ブロック分割部102から出力された符号化対象ブロック(CU)に含まれる判定ブロックから画像特徴量を算出して、当該判定ブロックが特定領域であるか否かを判定する。
First, the specific area determination unit 103 determines, for each determination block including a plurality of pixels included in the input image, whether the determination block is a specific area including a character or a line drawing (S110). Specifically, the specific area determination unit 103 calculates an image feature amount from a determination block included in the encoding target block (CU) output from the block division unit 102, and determines whether the determination block is a specific area. Determine whether or not.
ここで、特定領域判定部103は、例えば、輝度成分に基づく情報を画像特徴量として算出する。文字又は線画の輝度成分は、一般的に、高輝度と低輝度とに大きく集中し、小さな範囲で輝度が極端に変化する。したがって、隣接する画素間の輝度成分の傾斜は、大きくなる傾向がある。
Here, the specific area determination unit 103 calculates, for example, information based on a luminance component as an image feature amount. The luminance component of a character or line drawing is generally concentrated on high luminance and low luminance, and the luminance changes extremely in a small range. Therefore, the inclination of the luminance component between adjacent pixels tends to increase.
特定領域判定部103は、例えば、隣接する画素間の輝度差を画像特徴量として算出する。特定領域判定部103は、判定ブロックの中における画素の割合であって、隣接する画素間の輝度差が大きい画素の割合が、所定の割合以上の場合は、当該判定ブロックが特定領域であると判定する。
The specific area determination unit 103 calculates, for example, a luminance difference between adjacent pixels as an image feature amount. The specific area determination unit 103 indicates that the determination block is a specific area when the ratio of pixels in the determination block and the ratio of pixels having a large luminance difference between adjacent pixels is equal to or greater than a predetermined ratio. judge.
具体的には、特定領域判定部103は、隣接する画素間の輝度値の差分を算出する。そして、特定領域判定部103は、算出した差分が予め定められた第1閾値より大きいか否かを判定する。第1閾値より大きいと判定した場合、当該隣接する画素は、輝度差が大きい画素であると判定する。特定領域判定部103は、判定ブロックに含まれる全ての画素に対して、輝度値の差分と第1閾値との比較を行う。第1閾値は、例えば、輝度値の最小値と最大値との差の50%以上の値である。
Specifically, the specific area determination unit 103 calculates a difference in luminance value between adjacent pixels. Then, the specific area determination unit 103 determines whether or not the calculated difference is greater than a predetermined first threshold value. When it is determined that the pixel is larger than the first threshold, the adjacent pixel is determined to be a pixel having a large luminance difference. The specific area determination unit 103 compares the difference between the luminance values with the first threshold value for all the pixels included in the determination block. The first threshold value is, for example, a value that is 50% or more of the difference between the minimum value and the maximum value of the luminance values.
さらに、特定領域判定部103は、輝度差が大きい画素と判定した画素が、判定ブロックの中で占める割合を算出する。そして、特定領域判定部103は、算出した割合が所定の割合(第2閾値)以上であるか否かを判定する。例えば、特定領域判定部103は、画素の割合が第2閾値以上であるか否かを判定する。画素の割合が第2閾値以上である場合、特定領域判定部103は、判定ブロックが特定領域であると判定する。第2閾値は、例えば、20%以上の値である。
Furthermore, the specific area determination unit 103 calculates a ratio of pixels determined to be pixels having a large luminance difference in the determination block. Then, the specific area determination unit 103 determines whether or not the calculated ratio is greater than or equal to a predetermined ratio (second threshold). For example, the specific area determination unit 103 determines whether or not the pixel ratio is equal to or greater than the second threshold. When the pixel ratio is equal to or greater than the second threshold, the specific area determination unit 103 determines that the determination block is a specific area. The second threshold is a value of 20% or more, for example.
なお、上記においては、輝度成分を画像特徴量の基準としたが、符号化対象ピクチャから算出される情報であればどのような基準でも構わない。
In the above description, the luminance component is used as the reference for the image feature amount. However, any reference may be used as long as it is information calculated from the picture to be encoded.
また、特定領域判定部103は、判定ブロックのサイズを、例えば、8×8画素に設定する。本実施の形態では、後述するように特定領域と判定された判定ブロックを4×4画素の変換処理単位で直交変換する。このため、判定ブロックのサイズは、4×4画素以上の大きさであればよい。しかし、判定ブロックが4×4画素の場合、1つの判定ブロックあたりの画素サンプル数が少なく、ノイズに影響され誤判定が多くなる。したがって、特定領域を判断する判定ブロックは、8×8画素からなるブロックであることが好ましい。
Further, the specific area determination unit 103 sets the size of the determination block to 8 × 8 pixels, for example. In the present embodiment, as will be described later, a determination block determined to be a specific region is orthogonally converted in units of 4 × 4 pixel conversion processing. For this reason, the size of the determination block may be 4 × 4 pixels or more. However, when the determination block is 4 × 4 pixels, the number of pixel samples per determination block is small, and erroneous determination increases due to noise. Therefore, the determination block for determining the specific area is preferably a block composed of 8 × 8 pixels.
判定ブロックが特定領域であると判定した場合(S110でYes)、特定領域判定部103は、TUサイズとして4×4画素ブロックを常に選択する(S120)。一方、判定ブロックが特定領域でないと判断した場合(S110でNo)、特定領域判定部103は、32×32画素~4×4画素のうちいずれか1つをTUサイズとして選択する(S130)。TUサイズは、例えば、符号化対象ブロックに基づいて判断され、例えば、複雑な画像に対しては小さなTUサイズが、簡単な画像に対しては大きなTUサイズが選ばれる。
When it is determined that the determination block is a specific area (Yes in S110), the specific area determination unit 103 always selects a 4 × 4 pixel block as the TU size (S120). On the other hand, when it is determined that the determination block is not the specific area (No in S110), the specific area determination unit 103 selects any one of 32 × 32 pixels to 4 × 4 pixels as the TU size (S130). The TU size is determined based on, for example, the encoding target block. For example, a small TU size is selected for a complex image and a large TU size is selected for a simple image.
直交変換部105は、選択されたTU毎に判定ブロックの直交変換を選択的に行う(S140)。例えば、直交変換部105は、TUサイズが4×4画素の場合に、直交変換を行うことを選択した場合は、差分画像信号を直交変換することで、残差係数信号を生成して出力する。また、直交変換部105は、TUサイズが4×4画素の場合に、直交変換を行わないことを選択した場合は、差分画像信号をそのまま残差係数信号として出力する。また、直交変換部105は、TUサイズが4×4画素ではない場合、差分画像信号を必ず直交変換することで、残差係数信号を生成して出力する。なお、直交変換部105は、特定領域判定部103から出力されるTUを受け取ることで、TUサイズが4×4画素であるか否かを判定する。
The orthogonal transform unit 105 selectively performs orthogonal transform of the determination block for each selected TU (S140). For example, when the orthogonal transformation unit 105 selects to perform orthogonal transformation when the TU size is 4 × 4 pixels, the orthogonal transformation unit 105 performs orthogonal transformation on the difference image signal to generate and output a residual coefficient signal. . In addition, when the TU size is 4 × 4 pixels and the orthogonal transform unit 105 selects not to perform the orthogonal transform, the orthogonal transform unit 105 outputs the difference image signal as it is as a residual coefficient signal. Further, when the TU size is not 4 × 4 pixels, the orthogonal transform unit 105 generates and outputs a residual coefficient signal by performing orthogonal transform on the difference image signal. The orthogonal transform unit 105 receives the TU output from the specific region determination unit 103, and determines whether or not the TU size is 4 × 4 pixels.
なお、上記の説明では、TUサイズとして4×4画素を選択する処理では、特定領域判定部103がTUサイズを決める場合について説明したが、これに限らない。例えば、ブロック分割部102がTUサイズを決定した後で、特定領域判定部103がTUサイズを上書きすることで4×4画素に決定しても構わない。また、上記の説明では、ブロック分割部102が各々のブロックサイズを決めていたが、特定領域判定部103が決定したTUのサイズに応じてCU及びPUのサイズを決めても構わない。
In the above description, in the process of selecting 4 × 4 pixels as the TU size, the specific area determination unit 103 determines the TU size. However, the present invention is not limited to this. For example, after the block division unit 102 determines the TU size, the specific area determination unit 103 may determine 4 × 4 pixels by overwriting the TU size. In the above description, the block division unit 102 determines each block size. However, the CU and PU sizes may be determined according to the TU size determined by the specific area determination unit 103.
また、上記の説明では判定ブロックサイズを8×8画素としたが、4×4画素以上のサイズであれば、それ以外の予め定められたサイズでも構わない。この予め定められたサイズは、取得した入力画像内の1文字に占める画素数に依存して設定しても構わない。
In the above description, the determination block size is 8 × 8 pixels, but other predetermined sizes may be used as long as the size is 4 × 4 pixels or more. This predetermined size may be set depending on the number of pixels occupying one character in the acquired input image.
具体的には、特定領域判定部103は、入力画像内の1文字が1つの判定ブロックに収まるように判定ブロックサイズを決定してもよい。入力画像内の文字のサイズは、入力画像の画面解像度に依存する。例えば、雑誌又は新聞などを符号化する場合において、画面解像度が決定した場合、文字のサイズも自ずと決定することが多い。したがって、画面解像度に応じて判定ブロックを設定することで、1文字が1つの判定ブロックに収まるようにすることができる。
Specifically, the specific area determination unit 103 may determine the determination block size so that one character in the input image fits in one determination block. The size of characters in the input image depends on the screen resolution of the input image. For example, when encoding a magazine or a newspaper, when the screen resolution is determined, the character size is often determined naturally. Therefore, by setting the determination block according to the screen resolution, it is possible to fit one character into one determination block.
したがって、例えば、特定領域判定部103は、入力画像の画面解像度に応じて判定ブロックサイズを決定してもよい。具体的には、特定領域判定部103は、入力画像の画面解像度が1920×1080(フルHD)以上、3840×2160(4K2K)以下である場合に、判定ブロックサイズを8×8画素に決定してもよい。これにより、8×8画素の判定ブロック内に1文字が収まるようにすることができる。なお、この場合、エッジを含む判定ブロックの数を減らすこともできる。
Therefore, for example, the specific area determination unit 103 may determine the determination block size according to the screen resolution of the input image. Specifically, the specific area determination unit 103 determines the determination block size to be 8 × 8 pixels when the screen resolution of the input image is 1920 × 1080 (full HD) or more and 3840 × 2160 (4K2K) or less. May be. Thereby, it is possible to fit one character in the determination block of 8 × 8 pixels. In this case, the number of determination blocks including edges can be reduced.
また、特定領域判定部103は、判定ブロックサイズをCUサイズなどの、入力画像に対して非固定のサイズに決定しても構わない。つまり、特定領域判定部103は、判定ブロックのサイズをN×N画素(Nは4以上の整数)に設定してもよい。一例として、Nは8である。
Further, the specific area determination unit 103 may determine the determination block size to be a non-fixed size with respect to the input image, such as a CU size. That is, the specific area determination unit 103 may set the size of the determination block to N × N pixels (N is an integer of 4 or more). As an example, N is 8.
以上のように、特定領域判定部103によって、特定領域であると判定された判定ブロックのTUサイズが常に4×4画素ブロックに限定される。特定領域では、文字又は線画に接する周辺で高周波成分が多い。直交変換と量子化とにより、高周波成分の情報が失われやすくなるため、文字又は線画に接する周辺でノイズが発生しやすい。
As described above, the TU size of the determination block determined to be a specific region by the specific region determination unit 103 is always limited to a 4 × 4 pixel block. In the specific area, there are many high-frequency components around the character or line drawing. Since orthogonal transformation and quantization tend to lose high-frequency component information, noise is likely to occur in the vicinity of a character or line drawing.
そこで、4×4画素という小さなブロックサイズを用いて直交変換及び量子化を行うことで、ノイズの発生を小さなブロックに留めることができる。したがって、ブロックサイズが大きい場合より、符号化対象ピクチャ内における文字又は線画の領域に対する主観画質を向上させることができる。
Therefore, by performing orthogonal transformation and quantization using a small block size of 4 × 4 pixels, noise can be generated in a small block. Therefore, the subjective image quality for the character or line drawing area in the encoding target picture can be improved as compared with the case where the block size is large.
また、通常、TUサイズは4種類あり、複雑な分割方法によって決定される。このため、TUサイズを決定する際には、演算処理量が多くなる。しかし、特定領域を判定することにより、特定領域であると判定された判定ブロックのTUサイズを常に4×4画素ブロックと一意に設定することで、処理を省くことができる。そのため、文字又は線画の多い入力画像ほど演算処理量を大幅に削減できる。
Also, there are usually 4 types of TU sizes, which are determined by a complicated division method. For this reason, when determining the TU size, the amount of calculation processing increases. However, by determining the specific area, the processing block can be omitted by always uniquely setting the TU size of the determination block determined to be the specific area as a 4 × 4 pixel block. Therefore, the amount of calculation processing can be greatly reduced for input images with more characters or line drawings.
[まとめ]
本実施の形態に係る画像符号化装置は、入力画像を符号化する画像符号化装置100であって、入力画像に含まれる複数の画素からなる判定ブロック毎に、当該判定ブロックが文字又は線画を含む特定領域であるか否かを判定する特定領域判定部103と、複数の変換処理単位の中から適応的に選択された変換処理単位で、判定ブロックの直交変換を選択的に行うことで、残差係数を出力する直交変換部105とを備え、直交変換部105は、特定領域判定部103によって判定ブロックが特定領域であると判定された場合、常に4×4画素のブロックサイズに設定された変換処理単位毎に、判定ブロックの直交変換を選択的に行う。 [Summary]
The image encoding apparatus according to the present embodiment is animage encoding apparatus 100 that encodes an input image, and for each determination block including a plurality of pixels included in the input image, the determination block displays a character or a line drawing. By selectively performing orthogonal transform of the determination block in a specific region determination unit 103 that determines whether or not the specific region is included, and a transform processing unit adaptively selected from a plurality of transform processing units, An orthogonal transform unit 105 that outputs a residual coefficient. When the specific region determination unit 103 determines that the determination block is a specific region, the orthogonal transform unit 105 is always set to a block size of 4 × 4 pixels. For each transform processing unit, the orthogonal transform of the determination block is selectively performed.
本実施の形態に係る画像符号化装置は、入力画像を符号化する画像符号化装置100であって、入力画像に含まれる複数の画素からなる判定ブロック毎に、当該判定ブロックが文字又は線画を含む特定領域であるか否かを判定する特定領域判定部103と、複数の変換処理単位の中から適応的に選択された変換処理単位で、判定ブロックの直交変換を選択的に行うことで、残差係数を出力する直交変換部105とを備え、直交変換部105は、特定領域判定部103によって判定ブロックが特定領域であると判定された場合、常に4×4画素のブロックサイズに設定された変換処理単位毎に、判定ブロックの直交変換を選択的に行う。 [Summary]
The image encoding apparatus according to the present embodiment is an
このように、特定領域であると判定された判定ブロックでは、常に4×4画素のサイズで直交変換を行い、特定領域ではないと判定された判定ブロックでは、予め定められた複数のTUサイズの中から選択されたTUサイズで直交変換を行う。このとき、特定領域は、高周波成分が多いので、量子化によってノイズが発生しやすい領域である。しかしながら、発生したノイズは、4×4画素という小さなサイズに抑えられているので、主観的な画質を向上させることができる。
As described above, in the determination block determined to be the specific area, orthogonal transformation is always performed with a size of 4 × 4 pixels, and in the determination block determined not to be the specific area, a plurality of predetermined TU sizes are determined. Orthogonal transformation is performed with a TU size selected from among them. At this time, since the specific region has many high-frequency components, it is a region where noise is likely to occur due to quantization. However, since the generated noise is suppressed to a small size of 4 × 4 pixels, subjective image quality can be improved.
また、判定ブロックが特定領域であると判定された場合、当該判定ブロックのTUサイズとして常に4×4画素が一意的に決定されるので、TUサイズの決定に要する処理を省くことができ、演算処理量を削減することができる。このように、適したサイズで直交変換が行われることで、特定領域の高画質化が実現し、また、特定領域においてTUサイズを一意に決定できるため、演算処理量が削減できる。
Further, when it is determined that the determination block is a specific area, 4 × 4 pixels are always uniquely determined as the TU size of the determination block, so that the processing required to determine the TU size can be omitted, The amount of processing can be reduced. In this way, by performing orthogonal transformation with an appropriate size, high image quality of the specific area is realized, and the TU size can be uniquely determined in the specific area, so that the amount of calculation processing can be reduced.
(実施の形態2)
以下では、図3及び図4を用いて、実施の形態2を説明する。 (Embodiment 2)
Hereinafter, the second embodiment will be described with reference to FIGS. 3 and 4.
以下では、図3及び図4を用いて、実施の形態2を説明する。 (Embodiment 2)
Hereinafter, the second embodiment will be described with reference to FIGS. 3 and 4.
[画像符号化装置全体の処理説明]
図3は、本実施の形態に係る画像符号化装置200のブロック図である。画像符号化装置200は、ピクチャ単位で入力された画像をブロックに分割し、ブロック単位で符号化処理を行うことで、符号列を生成する。なお、実施の形態2において、実施の形態1と異なる点を中心に説明し、同一の構成については、説明を省略する場合がある。 [Description of Processing of Entire Image Encoding Device]
FIG. 3 is a block diagram ofimage coding apparatus 200 according to the present embodiment. The image coding apparatus 200 divides an image input in units of pictures into blocks and performs a coding process in units of blocks to generate a code string. Note that the second embodiment will be described with a focus on differences from the first embodiment, and the description of the same configuration may be omitted.
図3は、本実施の形態に係る画像符号化装置200のブロック図である。画像符号化装置200は、ピクチャ単位で入力された画像をブロックに分割し、ブロック単位で符号化処理を行うことで、符号列を生成する。なお、実施の形態2において、実施の形態1と異なる点を中心に説明し、同一の構成については、説明を省略する場合がある。 [Description of Processing of Entire Image Encoding Device]
FIG. 3 is a block diagram of
図3に示すように、本実施の形態に係る画像符号化装置200は、図1に示す画像符号化装置100と比べて、特定領域判定部103及び直交変換部105の代わりに、特定領域判定部203及び直交変換部205を備える点が異なっている。
As illustrated in FIG. 3, the image coding apparatus 200 according to the present embodiment is different from the image coding apparatus 100 illustrated in FIG. 1 in that the specific area determination unit 103 and the orthogonal transform unit 105 are replaced with a specific area determination unit. The difference is that the unit 203 and the orthogonal transform unit 205 are provided.
特定領域判定部203は、実施の形態1に示す動作に加えて、判定ブロックが特定領域であるか否かを判定した結果を直交変換部205に出力する。
The specific area determination unit 203 outputs, to the orthogonal transform unit 205, a result of determining whether or not the determination block is a specific area in addition to the operation shown in the first embodiment.
直交変換部205は、特定領域判定部203によって判定ブロックが特定領域ではないと判定された場合、判定ブロックの直交変換を必ず実行する。具体的には、直交変換部205は、特定領域判定部203から判定結果を受け取り、受け取った判定結果に基づいて直交変換を行うか否かを決定する。
When the specific region determination unit 203 determines that the determination block is not a specific region, the orthogonal transform unit 205 always executes orthogonal conversion of the determination block. Specifically, the orthogonal transform unit 205 receives the determination result from the specific region determination unit 203 and determines whether or not to perform orthogonal transform based on the received determination result.
HEVCでは、TUサイズが4×4画素の場合に限り、直交変換を行うか否かを選択可能である。しかしながら、本実施の形態では、特定領域判定部203によって判定ブロックが特定領域ではないと判定された場合に、TUサイズとして4×4画素のブロックが選択された場合であっても、直交変換部205は、必ず直交変換を実行する。
In HEVC, whether or not to perform orthogonal transformation can be selected only when the TU size is 4 × 4 pixels. However, in the present embodiment, when the specific area determination unit 203 determines that the determination block is not the specific area, even if a 4 × 4 pixel block is selected as the TU size, the orthogonal transform unit 205 always performs orthogonal transformation.
一方で、特定領域判定部203によって判定ブロックが特定領域であると判定された場合には、TUサイズとして常に4×4画素が選択される。この場合は、直交変換部205は、直交変換を選択的に実行することができる。
On the other hand, when the specific area determination unit 203 determines that the determination block is the specific area, 4 × 4 pixels are always selected as the TU size. In this case, the orthogonal transform unit 205 can selectively execute orthogonal transform.
[特定領域判定部及び直交変換部]
ここで、本実施の形態に係る特定領域判定部203及び直交変換部205における処理について、図4を用いて具体的に説明する。図4は、本実施の形態に係る特定領域の判定と直交変換処理とを示すフローチャートである。 [Specific area determination unit and orthogonal transform unit]
Here, the processing in the specificarea determination unit 203 and the orthogonal transform unit 205 according to the present embodiment will be specifically described with reference to FIG. FIG. 4 is a flowchart showing determination of a specific area and orthogonal transformation processing according to the present embodiment.
ここで、本実施の形態に係る特定領域判定部203及び直交変換部205における処理について、図4を用いて具体的に説明する。図4は、本実施の形態に係る特定領域の判定と直交変換処理とを示すフローチャートである。 [Specific area determination unit and orthogonal transform unit]
Here, the processing in the specific
ここで、TUのサイズを決定するまでの処理(S110~S130)は、図2と同じであるため、説明を省略する。
Here, the processing (S110 to S130) until the TU size is determined is the same as that shown in FIG.
判定ブロックが特定領域であると判定された場合(S110でYes)、判定ブロックのTUサイズとして常に4×4画素が選択される(S120)。このとき、直交変換部205は、4×4画素ブロック毎に判定ブロックに直交変換を選択的に実行する(S140)。
When it is determined that the determination block is a specific area (Yes in S110), 4 × 4 pixels are always selected as the TU size of the determination block (S120). At this time, the orthogonal transform unit 205 selectively performs orthogonal transform on the determination block for each 4 × 4 pixel block (S140).
例えば、直交変換部205は、直交変換しない場合よりも直交変換した場合に得られる再構成画像と入力画像との差分が小さい場合、直交変換の実行を選択する。一方で、直交変換部205は、直交変換する場合よりも直交変換しない場合に得られる再構成画像と入力画像との差分が小さい場合、直交変換を実行しないことを選択する。このように、直交変換部205は、判定ブロックが特定領域であると判定された場合は、実施の形態1と同様にして、直交変換を選択的に実行する。
For example, when the difference between the reconstructed image obtained when orthogonal transformation is performed and the input image is smaller than when orthogonal transformation is not performed, the orthogonal transformation unit 205 selects execution of orthogonal transformation. On the other hand, the orthogonal transform unit 205 selects not to perform orthogonal transform when the difference between the reconstructed image obtained when not performing orthogonal transform and the input image is smaller than when performing orthogonal transform. As described above, when it is determined that the determination block is the specific region, the orthogonal transform unit 205 selectively performs orthogonal transform in the same manner as in the first embodiment.
一方で、判定ブロックが特定領域ではないと判定された場合(S120でNo)、判定ブロックのTUサイズとして4×4画素~32×32画素のうちいずれか1つが選択される。この場合、直交変換部205は、選択されたTUサイズで常に直交変換を行う(S250)。
On the other hand, if it is determined that the determination block is not a specific area (No in S120), any one of 4 × 4 pixels to 32 × 32 pixels is selected as the TU size of the determination block. In this case, the orthogonal transform unit 205 always performs orthogonal transform with the selected TU size (S250).
例えば、直交変換部205は、TUサイズとして4×4画素が選択された場合は、通常であれば、直交変換を実行するか否かを選択可能である。しかしながら、直交変換を行うか否かを全ての4×4画素のブロックで判定することは、多大な演算処理量を必要とする。
For example, when 4 × 4 pixels are selected as the TU size, the orthogonal transform unit 205 can normally select whether to perform orthogonal transform. However, determining whether or not to perform orthogonal transformation in all 4 × 4 pixel blocks requires a large amount of calculation processing.
これに対して、本実施の形態に係る直交変換部205は、判定ブロックが特定領域ではないと判定された場合に、TUサイズが4×4画素が選択されたとしても、直交変換を必ず実行する。これにより、直交変換を行うか否かを決定するのに要する演算処理量を削減することができる。
On the other hand, the orthogonal transform unit 205 according to the present embodiment always performs orthogonal transform even when it is determined that the determination block is not a specific region, even if a TU size of 4 × 4 pixels is selected. To do. Thereby, the amount of calculation processing required to determine whether or not to perform orthogonal transform can be reduced.
特定領域ではないと判定された判定ブロックは、文字又は線画を含まない領域、例えば、自然画などである。このため、直交変換及び量子化によって高周波成分が失われたとしても、主観的には目立たない。つまり、主観的な画質は劣化しない。
The determination block determined not to be a specific area is an area that does not include characters or line drawings, such as a natural image. For this reason, even if a high frequency component is lost by orthogonal transformation and quantization, it is not conspicuous subjectively. That is, subjective image quality does not deteriorate.
一方で、特定領域であると判定された領域は、文字又は線画を含む領域であるので、上述したように、高周波成分が失われた場合には、ノイズが目立ち、主観的な画質が劣化する場合がある。このため、直交変換を行わない方が主観的な画質が良い場合は、直交変換部205が直交変換を行わないと選択することで、主観的な画質を向上させることができる。
On the other hand, since the area determined to be a specific area is an area including characters or line drawings, as described above, when high frequency components are lost, noise is noticeable and subjective image quality deteriorates. There is a case. For this reason, when the subjective image quality is better when the orthogonal transform is not performed, the subjective image quality can be improved by selecting the orthogonal transform unit 205 not to perform the orthogonal transform.
以上のように、特定領域判定部203及び直交変換部205によって、判定ブロックが文字又は線画を含む特定領域である場合、判定ブロックのTUサイズを常に4×4画素ブロックとして一意に設定できる。さらに、特定領域に対してのみ直交変換を行うか否かを切り替えて動作させることができる。
As described above, when the determination block is a specific region including a character or a line drawing, the TU size of the determination block can always be uniquely set as a 4 × 4 pixel block by the specific region determination unit 203 and the orthogonal transform unit 205. Furthermore, it can be operated by switching whether or not to perform orthogonal transform only on a specific region.
HEVCでは、4×4画素ブロックにおいて、直交変換を行うか否かを切り替えることができ、高画質化に効果的である。しかしながら、全ての4×4画素ブロックで直交変換を行うか否かを切り替えた場合、処理量が大幅に増加する。
HEVC can switch whether or not to perform orthogonal transformation in a 4 × 4 pixel block, which is effective in improving image quality. However, when switching whether or not to perform orthogonal transform on all 4 × 4 pixel blocks, the amount of processing increases significantly.
そこで、本実施の形態のように、直交変換を行うか否かを切り替えると効果の大きい特定領域である場合にのみ、選択的な直交変換を行うことで、処理量を大幅に増加させることなく、適した直交変換及び量子化処理が行うことができる。これにより、符号化対象ピクチャ内における特定領域に対して高い符号化効率を得ることができ、符号化後における画像の主観画質の向上及び演算処理量の増加を抑制させることができる。
Therefore, as in the present embodiment, switching between whether or not to perform orthogonal transformation is performed only when the specific region has a large effect, and selective orthogonal transformation is performed without significantly increasing the processing amount. Suitable orthogonal transformation and quantization processing can be performed. As a result, high coding efficiency can be obtained for a specific area in the picture to be coded, and improvement in the subjective image quality of the image after coding and increase in the amount of calculation processing can be suppressed.
また、特定領域でない領域では、周波数成分が特定の成分に集中せず広がりを持つ。そのため、常に直交変換を行うことで、符号化効率を向上させることができる。
Also, in a region that is not a specific region, the frequency component spreads without concentrating on the specific component. Therefore, encoding efficiency can be improved by always performing orthogonal transform.
[まとめ]
本実施の形態に係る画像符号化装置では、直交変換部205は、特定領域判定部203によって判定ブロックが特定領域ではないと判定された場合、判定ブロックの直交変換を必ず実行する。 [Summary]
In the image coding apparatus according to the present embodiment,orthogonal transform section 205 always performs orthogonal transform of a determination block when it is determined by specific area determination section 203 that the determination block is not a specific area.
本実施の形態に係る画像符号化装置では、直交変換部205は、特定領域判定部203によって判定ブロックが特定領域ではないと判定された場合、判定ブロックの直交変換を必ず実行する。 [Summary]
In the image coding apparatus according to the present embodiment,
これにより、特定領域ではないと判定された場合には直交変換を必ず実行するので、直交変換を行うか否かを決定するのに要する処理量を削減することができる。一方で、特定領域であると判定された場合には、主観画質が向上するように選択的に直交変換を行うことができる。このように、必要な場合にのみ、適応的に直交変換を行うか否かを切り替えることができるため、演算処理量を抑えつつ、主観画質の向上及び符号化効率の向上を実現できる。
Thus, orthogonal transformation is always executed when it is determined that the region is not a specific region, so that it is possible to reduce the amount of processing required to determine whether or not to perform orthogonal transformation. On the other hand, if it is determined that the region is a specific region, orthogonal transformation can be selectively performed so that the subjective image quality is improved. In this way, whether or not to perform orthogonal transform can be switched adaptively only when necessary, so that it is possible to realize improvement in subjective image quality and improvement in coding efficiency while suppressing the amount of calculation processing.
なお、例えば、図5に示すように、判定ブロックが特定領域であると判定された場合にも(S110でYes)、直交変換部205は、4×4画素ブロック毎に判定ブロックに直交変換を必ず実行してもよい。なお、図5は、本実施の形態の変形例に係る特定領域の判定と直交変換処理とを示すフローチャートである。
For example, as illustrated in FIG. 5, even when the determination block is determined to be a specific region (Yes in S110), the orthogonal transform unit 205 performs orthogonal transform on the determination block for each 4 × 4 pixel block. You may do it. FIG. 5 is a flowchart illustrating specific area determination and orthogonal transform processing according to a modification of the present embodiment.
図5に示すように、判定ブロックが特定領域であると判定された場合(S110でYes)、及び、判定ブロックが特定領域ではないと判定された場合(S110でNo)のいずれの場合でも、直交変換部205は、設定された変換処理単位毎に、判定ブロックの直交変換を必ず実行する(S250)。つまり、特定領域判定部203の判定結果によらず、直交変換部205は、直交変換を必ず実行してもよい。言い換えると、判定ブロックが特定領域であるか否かに関わらず、直交変換部205は、直交変換を必ず実行してもよい。
As shown in FIG. 5, whether the determination block is determined to be a specific area (Yes in S110) or the determination block is determined not to be a specific area (No in S110), The orthogonal transform unit 205 always performs orthogonal transform of the determination block for each set transform processing unit (S250). That is, regardless of the determination result of the specific area determination unit 203, the orthogonal transform unit 205 may always execute the orthogonal transform. In other words, regardless of whether or not the determination block is a specific region, the orthogonal transform unit 205 may always perform orthogonal transform.
このように、本実施の形態の変形例に係る画像符号化装置では、直交変換部205は、特定領域判定部203によって判定ブロックが特定領域であると判定された場合、常に4×4画素のブロックサイズに設定された変換処理単位毎に、判定ブロックの直交変換を必ず実行する。
Thus, in the image coding apparatus according to the modification of the present embodiment, the orthogonal transform unit 205 always has 4 × 4 pixels when the specific region determination unit 203 determines that the determination block is a specific region. The orthogonal transform of the determination block is always executed for each transform processing unit set to the block size.
これにより、4×4画素ブロックで直交変換を行うか否かを判定するのに要する処理を削減することができるので、演算処理量を削減することができる。
This makes it possible to reduce the processing required to determine whether or not to perform orthogonal transformation with a 4 × 4 pixel block, thereby reducing the amount of calculation processing.
(実施の形態3)
以下では、図6~図8を用いて、実施の形態3を説明する。 (Embodiment 3)
Hereinafter, Embodiment 3 will be described with reference to FIGS.
以下では、図6~図8を用いて、実施の形態3を説明する。 (Embodiment 3)
Hereinafter, Embodiment 3 will be described with reference to FIGS.
[画像符号化装置全体の処理説明]
図6は、本実施の形態に係る画像符号化装置300のブロック図である。画像符号化装置300は、ピクチャ単位で入力された画像をブロックに分割し、ブロック単位で符号化処理を行うことで、符号列を生成する。なお、実施の形態3において、実施の形態1と異なる点を中心に説明し、同一の構成については、説明を省略する場合がある。 [Description of Processing of Entire Image Encoding Device]
FIG. 6 is a block diagram of animage coding apparatus 300 according to the present embodiment. The image encoding device 300 divides an image input in units of pictures into blocks, and performs an encoding process in units of blocks to generate a code string. Note that the third embodiment will be described with a focus on differences from the first embodiment, and the description of the same configuration may be omitted.
図6は、本実施の形態に係る画像符号化装置300のブロック図である。画像符号化装置300は、ピクチャ単位で入力された画像をブロックに分割し、ブロック単位で符号化処理を行うことで、符号列を生成する。なお、実施の形態3において、実施の形態1と異なる点を中心に説明し、同一の構成については、説明を省略する場合がある。 [Description of Processing of Entire Image Encoding Device]
FIG. 6 is a block diagram of an
図6に示すように、本実施の形態に係る画像符号化装置300は、図1に示す画像符号化装置100と比べて、特定領域判定部103の代わりに特定領域判定部303を備える点と、新たに量子化パラメータ設定部312を備える点とが異なっている。
As illustrated in FIG. 6, the image coding apparatus 300 according to the present embodiment includes a specific area determination unit 303 instead of the specific area determination unit 103 as compared to the image coding apparatus 100 illustrated in FIG. 1. The difference is that a quantization parameter setting unit 312 is newly provided.
なお、特定領域判定部303は、実施の形態1に示す動作に加えて、判定ブロックが特定領域であるか否かを判定した結果を量子化パラメータ設定部312に出力する。
It should be noted that the specific area determination unit 303 outputs the result of determining whether or not the determination block is a specific area to the quantization parameter setting unit 312 in addition to the operation described in the first embodiment.
量子化パラメータ設定部312は、特定領域判定部303から出力される判定結果を用いて、量子化部106で利用する量子化パラメータの設定を行う。
The quantization parameter setting unit 312 sets a quantization parameter used by the quantization unit 106 using the determination result output from the specific region determination unit 303.
具体的には、量子化パラメータ設定部312は、予め定められた基準に基づいて量子化パラメータを所定の処理単位で設定する。例えば、量子化パラメータ設定部312は、レート制御などに基づいて量子化パラメータを所定の処理単位で設定する。具体的には、量子化パラメータ設定部312は、生成される符号列が所定のビットレートに近づくように量子化パラメータを設定する。ここで、所定の処理単位は、量子化パラメータを変更可能な処理単位である。例えば、所定の処理単位は、判定ブロックである。
Specifically, the quantization parameter setting unit 312 sets a quantization parameter in a predetermined processing unit based on a predetermined criterion. For example, the quantization parameter setting unit 312 sets the quantization parameter in a predetermined processing unit based on rate control or the like. Specifically, the quantization parameter setting unit 312 sets the quantization parameter so that the generated code string approaches a predetermined bit rate. Here, the predetermined processing unit is a processing unit in which the quantization parameter can be changed. For example, the predetermined processing unit is a determination block.
さらに、量子化パラメータ設定部312は、判定ブロックが特定領域である場合に、設定した量子化パラメータをより大きな値に再設定する。言い換えると、量子化パラメータ設定部312は、判定ブロックが特定領域である場合、判定ブロックが特定領域ではないと判定された場合に設定される量子化パラメータの値Q2より大きな値であるQ1に、量子化パラメータを設定する。
Further, the quantization parameter setting unit 312 resets the set quantization parameter to a larger value when the determination block is a specific region. In other words, when the determination block is a specific region, the quantization parameter setting unit 312 sets Q1 that is larger than the quantization parameter value Q2 set when it is determined that the determination block is not the specific region, Set the quantization parameter.
そして、量子化パラメータ設定部312は、設定した量子化パラメータを量子化部106に出力する。
Then, the quantization parameter setting unit 312 outputs the set quantization parameter to the quantization unit 106.
量子化部106は、直交変換部105から入力される残差係数信号に対してTU単位で量子化を行う。このとき、量子化部106は、量子化パラメータ設定部312で設定される量子化値(量子化パラメータ)及び量子化行列を用いて量子化を行うことで、量子化残差係数信号を生成する。量子化部106の詳細については、後述する。
The quantization unit 106 quantizes the residual coefficient signal input from the orthogonal transform unit 105 in units of TUs. At this time, the quantization unit 106 generates a quantization residual coefficient signal by performing quantization using the quantization value (quantization parameter) set by the quantization parameter setting unit 312 and the quantization matrix. . Details of the quantization unit 106 will be described later.
逆量子化部107は、量子化部106から入力される量子化残差係数信号に、当該量子化残差係数信号が量子化部106において量子化された際に用いられた量子化値(量子化パラメータ)及び量子化行列を用いて逆量子化することで、量子化残差係数信号を逆直交変換部108に出力する。
The inverse quantization unit 107 applies the quantization value (quantization value) used when the quantization residual coefficient signal input from the quantization unit 106 is quantized by the quantization unit 106 to the quantization residual coefficient signal. The quantization residual coefficient signal is output to the inverse orthogonal transform unit 108 by performing inverse quantization using the quantization parameter) and the quantization matrix.
[特定領域判定部、直交変換部及び量子化パラメータ設定部]
続いて、本実施の形態に係る特定領域判定部303、直交変換部105及び量子化パラメータ設定部312における処理について、図7及び図8を用いて具体的に説明する。図7は、本実施の形態に係る特定領域の判定と直交変換処理と量子化パラメータの設定とを示すフローチャートである。 [Specific area determination unit, orthogonal transform unit, and quantization parameter setting unit]
Subsequently, processing in the specificregion determination unit 303, the orthogonal transform unit 105, and the quantization parameter setting unit 312 according to the present embodiment will be specifically described with reference to FIGS. FIG. 7 is a flowchart showing specific area determination, orthogonal transform processing, and quantization parameter setting according to the present embodiment.
続いて、本実施の形態に係る特定領域判定部303、直交変換部105及び量子化パラメータ設定部312における処理について、図7及び図8を用いて具体的に説明する。図7は、本実施の形態に係る特定領域の判定と直交変換処理と量子化パラメータの設定とを示すフローチャートである。 [Specific area determination unit, orthogonal transform unit, and quantization parameter setting unit]
Subsequently, processing in the specific
ここで、TUのサイズの決定(S110~S130)と、直交変換(S140)とは、図2と同じであるため、説明を省略する。
Here, the determination of the TU size (S110 to S130) and the orthogonal transformation (S140) are the same as those in FIG.
判定ブロックが特定領域であると判定された場合(S110でYes)、量子化パラメータ設定部312は、量子化パラメータをQ1に設定する(S360)。
If it is determined that the determination block is a specific area (Yes in S110), the quantization parameter setting unit 312 sets the quantization parameter to Q1 (S360).
一方、判定ブロックが特定領域ではないと判定された場合(S110でNo)、量子化パラメータ設定部312は、量子化パラメータをQ2に設定する(S370)。
On the other hand, when it is determined that the determination block is not the specific region (No in S110), the quantization parameter setting unit 312 sets the quantization parameter to Q2 (S370).
量子化パラメータは、例えば、判定ブロック毎に設定される。量子化パラメータ設定部312は、判定ブロックが特定領域であるか否かに応じて、量子化パラメータを設定する。例えば、判定ブロックが特定領域である場合、判定ブロックの量子化に用いる量子化パラメータをQ1に、判定ブロックが特定領域ではない場合、判定ブロックの量子化に用いる量子化パラメータをQ2に設定する。
Quantization parameters are set for each determination block, for example. The quantization parameter setting unit 312 sets the quantization parameter according to whether or not the determination block is a specific region. For example, when the determination block is a specific region, the quantization parameter used for quantization of the determination block is set to Q1, and when the determination block is not the specific region, the quantization parameter used for quantization of the determination block is set to Q2.
Q1は、Q2以上の値に設定される。Q2は、特定領域と判定されない場合に設定される値であり、レート制御などに基づいて決定される値である。これに対して、量子化パラメータ設定部312は、レート制御などに基づいて決定されたQ2に、オフセットを加えることで、Q2より大きな値になるQ1を量子化パラメータとして設定する。これにより、特定領域と判定された判定ブロックを、粗く量子化することができる。
Q1 is set to a value equal to or greater than Q2. Q2 is a value set when it is not determined to be a specific area, and is a value determined based on rate control or the like. On the other hand, the quantization parameter setting unit 312 sets Q1 that is larger than Q2 as a quantization parameter by adding an offset to Q2 determined based on rate control or the like. Thereby, the determination block determined to be the specific region can be roughly quantized.
判定ブロックが特定領域である場合、TUサイズが常に4×4画素に設定される。これにより、特定領域の高画質化が実現しているが、TUがたくさん存在するため、オーバーヘッドが大きくなり、符号量増加につながる。そこで、特定領域の量子化パラメータを特定領域でない領域の量子化パラメータよりも大きな値に設定することで、符号量の増加を抑制することが可能となる。特定領域では、TUサイズが4×4画素の小さいブロックであるため、予測方向が当たりやすく、予測精度が高い。例えば、符号化対象の入力画像が自然画などの複雑な画像である場合でも、TUサイズが4×4画素の小さいブロックサイズであるために、TUは、単純な直線などの画像になる。このため、予測精度が高くなって、残差成分を減らすことができるため、粗く量子化しても画質が劣化しにくい。
When the determination block is a specific area, the TU size is always set to 4 × 4 pixels. As a result, high image quality is achieved in the specific area, but since there are many TUs, the overhead increases and the code amount increases. Thus, by setting the quantization parameter for the specific region to a value larger than the quantization parameter for the region that is not the specific region, it is possible to suppress an increase in the code amount. Since the specific area is a small block with a TU size of 4 × 4 pixels, the prediction direction is easy to hit and the prediction accuracy is high. For example, even if the input image to be encoded is a complex image such as a natural image, the TU is a simple block image because the TU size is a small block size of 4 × 4 pixels. For this reason, since prediction accuracy becomes high and a residual component can be reduced, even if it coarsely quantizes, an image quality does not deteriorate easily.
なお、上記の説明においては、判定ブロック毎に量子化パラメータを設定したが、量子化パラメータを設定する処理単位である所定の処理単位のサイズは、どのような基準でも構わない。例えば、所定の処理単位は、複数の判定ブロックから構成されてもよい。例えば、所定の処理単位は、CUでもよい。
In the above description, although the quantization parameter is set for each determination block, the size of the predetermined processing unit that is the processing unit for setting the quantization parameter may be any standard. For example, the predetermined processing unit may be composed of a plurality of determination blocks. For example, the predetermined processing unit may be a CU.
この場合、所定の処理単位には、判定ブロックが少なくとも1つ以上含まれる。つまり、所定の処理単位が判定ブロックのサイズ以上の大きさである。このように、複数の判定ブロックをまとめる場合、量子化パラメータ設定部312は、所定の処理単位内における特定領域であると判定された判定ブロックの割合に基づいて量子化パラメータを設定する。具体的には、量子化パラメータ設定部312は、所定の処理単位内における特定領域と判定された判定ブロックの割合が予め定められた閾値より大きい場合、予め定められた基準に基づいて決定される量子化値を、より大きな値に設定する。
In this case, the predetermined processing unit includes at least one determination block. That is, the predetermined processing unit is larger than the size of the determination block. As described above, when a plurality of determination blocks are collected, the quantization parameter setting unit 312 sets the quantization parameter based on the ratio of the determination blocks determined to be a specific area within a predetermined processing unit. Specifically, the quantization parameter setting unit 312 is determined based on a predetermined criterion when the ratio of the determination block determined as a specific region within a predetermined processing unit is larger than a predetermined threshold. Set the quantization value to a larger value.
例えば、所定の処理単位のサイズが32×32画素であり、その中に16個の8×8画素の判定ブロックが含まれている場合を想定する。このとき、16個の判定ブロックのうち特定領域と判定された判定ブロックが8個以上存在すると判定した場合に、量子化パラメータ設定部312は、特定領域と判定された判定ブロックが7個以下存在すると判定した場合に比べて、量子化パラメータを大きくする。
For example, it is assumed that the size of a predetermined processing unit is 32 × 32 pixels, and 16 8 × 8 pixel determination blocks are included therein. At this time, when it is determined that there are 8 or more determination blocks determined to be the specific region among the 16 determination blocks, the quantization parameter setting unit 312 has 7 or less determination blocks determined to be the specific region. Then, the quantization parameter is increased as compared with the case where it is determined.
ここで、量子化パラメータの設定方法の一例について、図8を用いて説明する。図8は、本実施の形態に係る量子化パラメータの設定を示すフローチャートである。
Here, an example of a quantization parameter setting method will be described with reference to FIG. FIG. 8 is a flowchart showing the setting of the quantization parameter according to the present embodiment.
まず、量子化パラメータ設定部312は、予め定められた基準に基づいて量子化パラメータをQ2に設定する(S361)。例えば、量子化パラメータ設定部312は、レート制御などに基づいて量子化パラメータを決定する。
First, the quantization parameter setting unit 312 sets the quantization parameter to Q2 based on a predetermined criterion (S361). For example, the quantization parameter setting unit 312 determines the quantization parameter based on rate control or the like.
次に、量子化パラメータ設定部312は、所定の処理単位内における特定領域と判定された判定ブロックの割合が、予め定められた閾値より大きいか否かを判定する(S362)。
Next, the quantization parameter setting unit 312 determines whether or not the ratio of the determination block determined as the specific area within the predetermined processing unit is larger than a predetermined threshold (S362).
特定領域と判定された判定ブロックの割合が閾値より大きい場合(S362でYes)、量子化パラメータ設定部312は、Q2にオフセットを加えることで、Q2より大きい値であるQ1を量子化パラメータとして設定する(S363)。特定領域と判定された判定ブロックの割合が閾値以下である場合(S362でNo)、量子化パラメータ設定部312は、Q2に設定された量子化パラメータをそのまま量子化部106に出力する。
When the ratio of the determination blocks determined as the specific region is larger than the threshold (Yes in S362), the quantization parameter setting unit 312 sets Q1 that is a value larger than Q2 as a quantization parameter by adding an offset to Q2. (S363). When the ratio of the determination blocks determined as the specific region is equal to or less than the threshold (No in S362), the quantization parameter setting unit 312 outputs the quantization parameter set in Q2 to the quantization unit 106 as it is.
このように、量子化パラメータ設定部312は、特定領域と判定された判定ブロックの割合が閾値より大きい場合の量子化パラメータとして、特定領域と判定された判定ブロックの割合が閾値以下である場合の量子化パラメータより大きな値を設定する。
As described above, the quantization parameter setting unit 312 uses the case where the ratio of the determination blocks determined as the specific area is equal to or less than the threshold as the quantization parameter when the ratio of the determination blocks determined as the specific area is larger than the threshold. Set a value larger than the quantization parameter.
[まとめ]
本実施の形態に係る画像符号化装置300は、特定領域判定部303によって特定領域であると判定された判定ブロックの量子化パラメータを、当該判定ブロックが特定領域ではないと判定された場合に設定される量子化パラメータより大きな値に設定する量子化パラメータ設定部312と、量子化パラメータ設定部312によって設定された量子化値を用いて残差係数を量子化する量子化部106とを備える。 [Summary]
Image coding apparatus 300 according to the present embodiment sets a quantization parameter of a determination block that is determined to be a specific region by specific region determination unit 303 when it is determined that the determination block is not a specific region. A quantization parameter setting unit 312 for setting a value larger than the quantization parameter to be set, and a quantization unit 106 for quantizing the residual coefficient using the quantization value set by the quantization parameter setting unit 312.
本実施の形態に係る画像符号化装置300は、特定領域判定部303によって特定領域であると判定された判定ブロックの量子化パラメータを、当該判定ブロックが特定領域ではないと判定された場合に設定される量子化パラメータより大きな値に設定する量子化パラメータ設定部312と、量子化パラメータ設定部312によって設定された量子化値を用いて残差係数を量子化する量子化部106とを備える。 [Summary]
これにより、特定領域であると判定された判定ブロックの量子化パラメータを、特定領域でないと判定された場合に設定される量子化パラメータより大きな値にするので、特定領域と判定された判定ブロックの符号量を削減することができる。また、特定領域と判定された判定ブロックは、TUサイズとして4×4画素、すなわち、小さいブロックが選択されるので、画質の劣化は目立ちにくい。したがって、特定領域の主観画質の劣化を抑制し、かつ、符号量を削減することができる。
As a result, the quantization parameter of the determination block determined to be the specific region is set to a value larger than the quantization parameter set when the determination block is determined not to be the specific region. The amount of codes can be reduced. In addition, since the determination block determined as the specific area is selected as a TU size of 4 × 4 pixels, that is, a small block, deterioration in image quality is not conspicuous. Therefore, it is possible to suppress deterioration of the subjective image quality of the specific area and reduce the code amount.
また、本実施の形態に係る画像符号化装置300は、量子化値を設定する処理単位である所定の処理単位が判定ブロックのサイズ以上である場合において、所定の処理単位内における特定領域であると判定された判定ブロックの割合が予め定められた閾値より大きい場合の量子化パラメータを、所定の処理単位内における特定領域と判定された判定ブロックの割合が閾値以下である場合の量子化パラメータより大きな値に設定する量子化パラメータ設定部312と、量子化パラメータ設定部312によって設定された量子化値を用いて残差係数を量子化する量子化部106とを備えてもよい。
In addition, image coding apparatus 300 according to the present embodiment is a specific region in a predetermined processing unit when a predetermined processing unit that is a processing unit for setting a quantization value is equal to or larger than the size of the determination block. The quantization parameter when the ratio of the determination block determined to be greater than a predetermined threshold is greater than the quantization parameter when the ratio of the determination block determined as a specific area within a predetermined processing unit is equal to or less than the threshold. You may provide the quantization parameter setting part 312 set to a big value, and the quantization part 106 which quantizes a residual coefficient using the quantization value set by the quantization parameter setting part 312.
これにより、特定領域の割合が大きい領域の量子化パラメータを、特定領域の割合が小さい領域の量子化パラメータより大きな値にするので、特定領域の割合が大きい領域の符号量を削減することができる。
As a result, the quantization parameter of the region having a large ratio of the specific region is set to a larger value than the quantization parameter of the region having a small ratio of the specific region, so that the code amount of the region having a large ratio of the specific region can be reduced. .
(実施の形態4)
以下では、図9及び図10を用いて、実施の形態4を説明する。 (Embodiment 4)
Hereinafter, the fourth embodiment will be described with reference to FIGS. 9 and 10.
以下では、図9及び図10を用いて、実施の形態4を説明する。 (Embodiment 4)
Hereinafter, the fourth embodiment will be described with reference to FIGS. 9 and 10.
なお、実施の形態4は、上述した実施の形態2と実施の形態3とを組み合わせた実施の形態である。
Note that the fourth embodiment is an embodiment in which the second embodiment and the third embodiment described above are combined.
[画像符号化装置全体の処理説明]
図9は、実施の形態の変形例に係る画像符号化装置400のブロック図である。画像符号化装置400は、ピクチャ単位で入力された画像をブロックに分割し、ブロック単位で符号化処理を行うことで、符号列を生成する。なお、実施の形態4において、実施の形態2及び3と異なる点を中心に説明し、同一の構成については、説明を省略する場合がある。 [Description of Processing of Entire Image Encoding Device]
FIG. 9 is a block diagram of animage encoding device 400 according to a modification of the embodiment. The image coding apparatus 400 divides an image input in units of pictures into blocks, and performs a coding process in units of blocks to generate a code string. In the fourth embodiment, differences from the second and third embodiments will be mainly described, and the description of the same configuration may be omitted.
図9は、実施の形態の変形例に係る画像符号化装置400のブロック図である。画像符号化装置400は、ピクチャ単位で入力された画像をブロックに分割し、ブロック単位で符号化処理を行うことで、符号列を生成する。なお、実施の形態4において、実施の形態2及び3と異なる点を中心に説明し、同一の構成については、説明を省略する場合がある。 [Description of Processing of Entire Image Encoding Device]
FIG. 9 is a block diagram of an
図9に示すように、画像符号化装置400は、図6に示す実施の形態3に係る画像符号化装置300と比べて、直交変換部105の代わりに直交変換部205を備える点が異なっている。直交変換部205は、実施の形態2に係る直交変換部205と同一の構成である。
As shown in FIG. 9, image coding apparatus 400 differs from image coding apparatus 300 according to Embodiment 3 shown in FIG. 6 in that it includes orthogonal transform section 205 instead of orthogonal transform section 105. Yes. The orthogonal transform unit 205 has the same configuration as the orthogonal transform unit 205 according to the second embodiment.
[特定領域判定部、直交変換部及び量子化パラメータ設定部]
続いて、本実施の形態に係る特定領域判定部303、直交変換部205及び量子化パラメータ設定部312における処理について、図10を用いて説明する。図10は、実施の形態の変形例に係る特定領域の判定と直交変換処理と量子化パラメータの設定とを示すフローチャートである。 [Specific area determination unit, orthogonal transform unit, and quantization parameter setting unit]
Subsequently, processing in the specificregion determination unit 303, the orthogonal transform unit 205, and the quantization parameter setting unit 312 according to the present embodiment will be described with reference to FIG. FIG. 10 is a flowchart illustrating specific area determination, orthogonal transform processing, and quantization parameter setting according to a modification of the embodiment.
続いて、本実施の形態に係る特定領域判定部303、直交変換部205及び量子化パラメータ設定部312における処理について、図10を用いて説明する。図10は、実施の形態の変形例に係る特定領域の判定と直交変換処理と量子化パラメータの設定とを示すフローチャートである。 [Specific area determination unit, orthogonal transform unit, and quantization parameter setting unit]
Subsequently, processing in the specific
図10に示すように、TUのサイズを決定するまでの処理(S110~S130)と、直交変換の選択的な実行(S140)及び直交変換の実行(S250)とは、実施の形態2で説明した図4と同じである。量子化パラメータの設定(S360及びS370)は、実施の形態3で説明した図8と同じである。
As shown in FIG. 10, the processing until the TU size is determined (S110 to S130), the selective execution of orthogonal transform (S140), and the execution of orthogonal transform (S250) are described in the second embodiment. It is the same as FIG. The quantization parameter setting (S360 and S370) is the same as that in FIG. 8 described in the third embodiment.
[まとめ]
以上のように、本実施の形態に係る画像符号化装置400では、特定領域であると判定された判定ブロックには、TUサイズとして選択された4×4画素のブロック毎に、直交変換が選択的に実行される。さらに、特定領域であると判定された判定ブロックの量子化に用いる量子化パラメータは、特定領域ではないと判定された場合に設定される量子化パラメータの値Q2より大きな値であるQ1に設定される。 [Summary]
As described above, inimage coding apparatus 400 according to the present embodiment, orthogonal transform is selected for each block of 4 × 4 pixels selected as a TU size for a determination block determined to be a specific region. Is executed automatically. Further, the quantization parameter used for quantization of the determination block determined to be the specific region is set to Q1 which is a value larger than the quantization parameter value Q2 set when it is determined that the determination block is not the specific region. The
以上のように、本実施の形態に係る画像符号化装置400では、特定領域であると判定された判定ブロックには、TUサイズとして選択された4×4画素のブロック毎に、直交変換が選択的に実行される。さらに、特定領域であると判定された判定ブロックの量子化に用いる量子化パラメータは、特定領域ではないと判定された場合に設定される量子化パラメータの値Q2より大きな値であるQ1に設定される。 [Summary]
As described above, in
これにより、例えば、4×4画素のブロックに直交変換が実行されない場合、量子化の対象となる残差係数は、周波数領域ではなく空間領域の値である。具体的には、残差係数は、輝度値の差分を示している。空間領域で量子化が行われるので、高周波成分が失われるという影響は現れず、画質の劣化を抑制することができる。
Thus, for example, when orthogonal transformation is not performed on a 4 × 4 pixel block, the residual coefficient to be quantized is a value in the spatial domain, not the frequency domain. Specifically, the residual coefficient indicates a difference in luminance value. Since quantization is performed in the spatial domain, the effect of losing high-frequency components does not appear and image quality deterioration can be suppressed.
また、特定領域は文字又は線画を含む領域であるので、自然画に比べてイントラ予測の精度もよく、残差係数は小さな値になる場合が多い。このため、TUのブロック数は多くなるが、1つのTUの符号量を削減することができ、全体としての符号量を抑制することもできる。このとき、特定領域と判定された判定ブロックに対する量子化パラメータを大きくするので、1つのTUの符号量をさらに削減することができる。
Also, since the specific area is an area including a character or a line drawing, the accuracy of intra prediction is better than that of a natural image, and the residual coefficient often has a small value. For this reason, although the number of TU blocks increases, the code amount of one TU can be reduced, and the code amount as a whole can also be suppressed. At this time, since the quantization parameter for the determination block determined as the specific region is increased, the code amount of one TU can be further reduced.
また、TUサイズが4×4画素の小さいブロックであるため、予測方向が当たりやすく、予測精度が高い。例えば、符号化対象の入力画像が自然画などの複雑な画像である場合でも、TUサイズが4×4画素の小さいブロックサイズであるために、TUは、単純な直線などの画像になり、予測精度が高くなる。
Also, since the TU size is a small block of 4 × 4 pixels, the prediction direction is easy to hit and the prediction accuracy is high. For example, even when the input image to be encoded is a complex image such as a natural image, the TU is a small block size of 4 × 4 pixels. Increases accuracy.
一方で、特定領域ではないと判定された判定ブロックでは、直交変換が必ず実行される。特定領域ではないと判定された判定ブロックは、自然画などの複雑な画像である。このため、直交変換及び量子化によって高周波成分が失われたとしても、主観的な画質の劣化は抑制される。したがって、主観的な画質を劣化させることなく、直交変換を行うか否かを決定するのに要する処理量を削減することができる。
On the other hand, orthogonal transformation is always executed in a determination block that is determined not to be a specific region. The determination block determined not to be the specific region is a complex image such as a natural image. For this reason, even if high frequency components are lost due to orthogonal transformation and quantization, subjective deterioration of image quality is suppressed. Therefore, it is possible to reduce the processing amount required to determine whether or not to perform orthogonal transformation without degrading subjective image quality.
以上のように、本実施の形態に係る画像符号化装置400によれば、主観画質を向上させ、かつ、演算処理量を削減することができる。
As described above, according to the image coding apparatus 400 according to the present embodiment, it is possible to improve the subjective image quality and reduce the amount of calculation processing.
なお、実施の形態2の変形例と同様に、例えば、図11に示すように、判定ブロックが特定領域であると判定された場合にも(S110でYes)、直交変換部205は、4×4画素ブロック毎に判定ブロックに直交変換を必ず実行してもよい。なお、図11は、本実施の形態の変形例に係る特定領域の判定と直交変換処理とを示すフローチャートである。
As in the modification of the second embodiment, for example, as illustrated in FIG. 11, even when the determination block is determined to be a specific region (Yes in S110), the orthogonal transform unit 205 is 4 × Orthogonal transformation may always be performed on the determination block every four pixel blocks. FIG. 11 is a flowchart illustrating specific area determination and orthogonal transform processing according to a modification of the present embodiment.
図11に示すように、判定ブロックが特定領域であると判定された場合(S110でYes)、及び、判定ブロックが特定領域ではないと判定された場合(S110でNo)のいずれの場合でも、直交変換部205は、設定された変換処理単位毎に、判定ブロックの直交変換を必ず実行する(S250)。つまり、特定領域判定部203の判定結果によらず、直交変換部205は、直交変換を必ず実行してもよい。言い換えると、判定ブロックが特定領域であるか否かに関わらず、直交変換部205は、直交変換を必ず実行してもよい。
As shown in FIG. 11, whether the determination block is determined to be a specific area (Yes in S110) or the determination block is determined not to be a specific area (No in S110), The orthogonal transform unit 205 always performs orthogonal transform of the determination block for each set transform processing unit (S250). That is, regardless of the determination result of the specific area determination unit 203, the orthogonal transform unit 205 may always execute the orthogonal transform. In other words, regardless of whether or not the determination block is a specific region, the orthogonal transform unit 205 may always perform orthogonal transform.
これにより、実施の形態2の変形例と同様に、4×4画素ブロックで直交変換を行うか否かを判定するのに要する処理を削減することができるので、演算処理量を削減することができる。
As a result, similar to the modification of the second embodiment, it is possible to reduce the processing required to determine whether or not to perform orthogonal transformation with a 4 × 4 pixel block, so that the amount of calculation processing can be reduced. it can.
(他の実施の形態)
以上のように、本出願において開示する技術の例示として、実施の形態1~4を説明した。しかしながら、本開示における技術は、これに限定されず、適宜、変更、置き換え、付加、省略などを行った実施の形態にも適用可能である。また、上記実施の形態1~4で説明した各構成要素を組み合わせて、新たな実施の形態とすることも可能である。 (Other embodiments)
As described above, Embodiments 1 to 4 have been described as examples of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can also be applied to an embodiment in which changes, replacements, additions, omissions, and the like are appropriately performed. In addition, it is possible to combine the components described in the first to fourth embodiments to form a new embodiment.
以上のように、本出願において開示する技術の例示として、実施の形態1~4を説明した。しかしながら、本開示における技術は、これに限定されず、適宜、変更、置き換え、付加、省略などを行った実施の形態にも適用可能である。また、上記実施の形態1~4で説明した各構成要素を組み合わせて、新たな実施の形態とすることも可能である。 (Other embodiments)
As described above, Embodiments 1 to 4 have been described as examples of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can also be applied to an embodiment in which changes, replacements, additions, omissions, and the like are appropriately performed. In addition, it is possible to combine the components described in the first to fourth embodiments to form a new embodiment.
例えば、実施の形態2の変形例及び実施の形態4の変形例において、判定ブロックが特定領域であるか否かに関わらず、直交変換部205は、設定された変換処理単位毎に、判定ブロックに直交変換を必ず実行する例について説明したが、これに限らない。例えば、実施の形態2とは逆に、直交変換部205は、判定ブロックが特定領域であると判定された場合(S110でYes)に、直交変換を必ず実行し、判定ブロックが特定領域ではないと判定された場合(S110でNo)に、直交変換を選択的に実行してもよい。この場合においても、判定ブロックが特定領域であると判定された場合には、直交変換を行うか否かを判定するのに要する処理を削減することができるので、演算処理量を削減することができる。
For example, in the modification of the second embodiment and the modification of the fourth embodiment, the orthogonal transform unit 205 determines the determination block for each set transform processing unit regardless of whether the determination block is a specific region. Although an example in which orthogonal transformation is always executed has been described, this is not restrictive. For example, contrary to Embodiment 2, when it is determined that the determination block is a specific region (Yes in S110), the orthogonal transform unit 205 always executes orthogonal transform and the determination block is not the specific region. (No in S110), the orthogonal transformation may be selectively executed. Even in this case, if it is determined that the determination block is a specific area, the processing required to determine whether or not to perform orthogonal transformation can be reduced, so that the amount of calculation processing can be reduced. it can.
実施の形態1~4では、各実施の形態に係る画像符号化装置が利用する符号化規格としてHEVC規格を説明した。符号化規格は、直交変換を選択的に実行できればよい。したがって、符号化規格は、HEVC規格に限定されない。
In Embodiments 1 to 4, the HEVC standard has been described as the encoding standard used by the image encoding apparatus according to each embodiment. The encoding standard only needs to selectively perform orthogonal transformation. Therefore, the encoding standard is not limited to the HEVC standard.
さらに、上記実施の形態で示した画像符号化装置に含まれる各手段と同等の機能を備えるプログラムを、フレキシブルディスク等の記録媒体に記録するようにすることにより、上記実施の形態で示した処理を、独立したコンピュータシステムにおいて簡単に実施することが可能となる。なお、記録媒体としてはフレキシブルディスクに限らず、光ディスク、ICカード、ROM(Read Only Memory)カセット等、プログラムを記録できるものであれば同様に実施することができる。
Furthermore, the processing described in the above embodiment is performed by recording a program having a function equivalent to each unit included in the image encoding device described in the above embodiment on a recording medium such as a flexible disk. Can be easily implemented in an independent computer system. The recording medium is not limited to a flexible disk, but can be similarly implemented as long as it can record a program, such as an optical disk, an IC card, and a ROM (Read Only Memory) cassette.
また、上記実施の形態で示した画像符号化装置に含まれる各手段と同等の機能を集積回路であるLSIとして実現してもよい。これらは一部又は全てを含むように1チップ化されてもよい。またLSIは集積度の違いにより、IC、システムLSI、スーパーLSI、ウルトラLSIと称されることもある。
In addition, a function equivalent to each unit included in the image encoding device shown in the above embodiment may be realized as an LSI which is an integrated circuit. These may be integrated into one chip so as to include a part or all of them. An LSI may also be called an IC, a system LSI, a super LSI, or an ultra LSI depending on the degree of integration.
また、集積回路化の手法はLSIに限るものではなく、専用回路又は汎用プロセッサで実現しても良い。LSI製造後に、プログラムすることが可能なFPGA(Field Programmable Gate Array)や、LSI内部の回路セルの接続や設定を再構成可能なリコンフィギュラブル・プロセッサを利用してもよい。
Further, the method of circuit integration is not limited to LSI, and implementation with a dedicated circuit or a general-purpose processor is also possible. An FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.
さらには、半導体技術の進歩又は派生する別技術によりLSIなどに置き換わる集積回路の技術が登場すれば、当然、その技術を用いて機能ブロックの集積化を行ってもよい。
Further, if integrated circuit technology that replaces LSI or the like appears due to progress in semiconductor technology or other derived technology, the functional blocks may naturally be integrated using this technology.
具体的には、本開示に係る画像符号化装置100、200、300及び400を構成する各構成要素(ピクチャメモリ101と、ブロック分割部102と、特定領域判定部103、203及び303と、差分演算部104と、直交変換部105及び205と、量子化部106と、逆量子化部107と、逆直交変換部108と、加算演算部109と、予測画像生成部110と、符号列生成部111と、量子化パラメータ設定部312と)は、CPU(Central Processing Unit)、RAM(Random Access Memory)、ROM、通信インターフェース、I/Oポート、ハードディスク、ディスプレイなどを備えるコンピュータ上で実行されるプログラムなどのソフトウェアで実現されてもよく、電子回路などのハードウェアで実現されてもよい。
Specifically, each component (the picture memory 101, the block division unit 102, the specific area determination units 103, 203, and 303, and the difference included in the image encoding devices 100, 200, 300, and 400 according to the present disclosure Operation unit 104, orthogonal transform units 105 and 205, quantization unit 106, inverse quantization unit 107, inverse orthogonal transform unit 108, addition operation unit 109, predicted image generation unit 110, and code string generation unit 111 and a quantization parameter setting unit 312) are programs executed on a computer including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM, a communication interface, an I / O port, a hard disk, a display, and the like. It may be realized by software such as It may be implemented in hardware such as circuit.
また、上記実施の形態に係る、画像符号化装置、又はその変形例の機能のうち少なくとも一部を組み合わせてもよい。
Further, at least a part of the functions of the image encoding device or its modification according to the above embodiment may be combined.
以上のように、本開示における技術の例示として、実施の形態を説明した。そのために、添付図面及び詳細な説明を提供した。
As described above, the embodiments have been described as examples of the technology in the present disclosure. For this purpose, the accompanying drawings and detailed description are provided.
したがって、添付図面及び詳細な説明に記載された構成要素の中には、課題解決のために必須な構成要素だけでなく、上記技術を例示するために、課題解決のためには必須でない構成要素も含まれ得る。そのため、それらの必須ではない構成要素が添付図面や詳細な説明に記載されていることをもって、直ちに、それらの必須ではない構成要素が必須であるとの認定をするべきではない。
Accordingly, among the components described in the attached drawings and detailed description, not only the components essential for solving the problem, but also the components not essential for solving the problem in order to exemplify the above technique. May also be included. Therefore, it should not be immediately recognized that these non-essential components are essential as those non-essential components are described in the accompanying drawings and detailed description.
また、上述の実施の形態は、本開示における技術を例示するためのものであるから、請求の範囲又はその均等の範囲において種々の変更、置き換え、付加、省略などを行うことができる。
In addition, since the above-described embodiment is for illustrating the technique in the present disclosure, various modifications, replacements, additions, omissions, and the like can be performed within the scope of the claims or an equivalent scope thereof.
本開示は、例えば、新聞又は雑誌等の紙面を静止画の画像データとして入力し、符号化処理を行うことで静止画像符号列として出力する画像符号化装置に有用である。また、文字又は図が多重化された映像を動画の画像データとして入力し、符号化処理を行うことで動画像符号列として出力する画像符号化装置として有用である。
The present disclosure is useful, for example, for an image encoding device that inputs a paper such as a newspaper or a magazine as image data of a still image and outputs it as a still image code string by performing an encoding process. In addition, the present invention is useful as an image encoding device that inputs video in which characters or figures are multiplexed as moving image data and outputs it as a moving image code string by performing encoding processing.
100、200、300、400 画像符号化装置
101 ピクチャメモリ
102 ブロック分割部
103、203、303 特定領域判定部
104 差分演算部
105、205 直交変換部
106 量子化部
107 逆量子化部
108 逆直交変換部
109 加算演算部
110 予測画像生成部
111 符号列生成部
312 量子化パラメータ設定部 100, 200, 300, 400Image coding apparatus 101 Picture memory 102 Block division unit 103, 203, 303 Specific area determination unit 104 Difference calculation unit 105, 205 Orthogonal transformation unit 106 Quantization unit 107 Inverse quantization unit 108 Inverse orthogonal transformation Unit 109 addition calculation unit 110 prediction image generation unit 111 code string generation unit 312 quantization parameter setting unit
101 ピクチャメモリ
102 ブロック分割部
103、203、303 特定領域判定部
104 差分演算部
105、205 直交変換部
106 量子化部
107 逆量子化部
108 逆直交変換部
109 加算演算部
110 予測画像生成部
111 符号列生成部
312 量子化パラメータ設定部 100, 200, 300, 400
Claims (8)
- 入力画像を符号化する画像符号化装置であって、
前記入力画像に含まれる複数の画素からなる判定ブロック毎に、当該判定ブロックが文字又は線画を含む特定領域であるか否かを判定する判定部と、
複数の変換処理単位の中から適応的に選択された変換処理単位で、前記判定ブロックの直交変換を選択的に行うことで、残差係数を出力する直交変換部とを備え、
前記直交変換部は、前記判定部によって前記判定ブロックが前記特定領域であると判定された場合、常に4×4画素のブロックサイズに設定された変換処理単位毎に、前記判定ブロックの直交変換を選択的に行う
画像符号化装置。 An image encoding device for encoding an input image,
A determination unit that determines, for each determination block including a plurality of pixels included in the input image, whether the determination block is a specific region including a character or a line drawing;
An orthogonal transformation unit that outputs a residual coefficient by selectively performing orthogonal transformation of the determination block in a transformation processing unit adaptively selected from a plurality of transformation processing units;
When the determination unit determines that the determination block is the specific area, the orthogonal conversion unit performs orthogonal conversion of the determination block for each conversion processing unit set to a block size of 4 × 4 pixels. An image encoding device that is selectively performed. - 前記直交変換部は、前記判定部によって前記判定ブロックが前記特定領域ではないと判定された場合、前記判定ブロックの直交変換を必ず実行する
請求項1に記載の画像符号化装置。 The image encoding device according to claim 1, wherein the orthogonal transform unit always performs orthogonal transform of the determination block when the determination unit determines that the determination block is not the specific region. - 前記直交変換部は、前記判定部によって前記判定ブロックが前記特定領域であると判定された場合、常に4×4画素のブロックサイズに設定された変換処理単位毎に、前記判定ブロックの直交変換を必ず実行する
請求項1又は2に記載の画像符号化装置。 When the determination unit determines that the determination block is the specific area, the orthogonal conversion unit performs orthogonal conversion of the determination block for each conversion processing unit set to a block size of 4 × 4 pixels. The image encoding apparatus according to claim 1 or 2, which is necessarily executed. - 前記判定部は、さらに、前記判定ブロックのサイズをN×N画素(Nは4以上の整数)に設定する
請求項1~3のいずれか1項に記載の画像符号化装置。 The image encoding device according to any one of claims 1 to 3, wherein the determination unit further sets the size of the determination block to N × N pixels (N is an integer of 4 or more). - 前記Nは、8である
請求項4に記載の画像符号化装置。 The image encoding device according to claim 4, wherein N is 8. 5. - 前記画像符号化装置は、さらに、
前記判定部によって前記特定領域であると判定された判定ブロックの量子化パラメータを、当該判定ブロックが前記特定領域ではないと判定された場合に設定される量子化パラメータより大きな値に設定する設定部と、
前記設定部によって設定された量子化値を用いて前記残差係数を量子化する量子化部とを備える
請求項1~5のいずれか1項に記載の画像符号化装置。 The image encoding device further includes:
A setting unit that sets a quantization parameter of a determination block determined to be the specific region by the determination unit to a value larger than a quantization parameter that is set when the determination block is determined not to be the specific region When,
6. The image encoding device according to claim 1, further comprising a quantization unit that quantizes the residual coefficient using a quantization value set by the setting unit. - 前記画像符号化装置は、さらに、
量子化値を設定する処理単位である所定の処理単位が前記判定ブロックのサイズ以上である場合において、前記所定の処理単位内における前記特定領域であると判定された判定ブロックの割合が予め定められた閾値より大きい場合の量子化パラメータを、前記所定の処理単位内における前記特定領域と判定された判定ブロックの割合が前記閾値以下である場合の量子化パラメータより大きな値に設定する設定部と、
前記設定部によって設定された量子化値を用いて前記残差係数を量子化する量子化部とを備える
請求項1~5のいずれか1項に記載の画像符号化装置。 The image encoding device further includes:
When a predetermined processing unit that is a processing unit for setting a quantization value is equal to or larger than the size of the determination block, a ratio of the determination block determined to be the specific area in the predetermined processing unit is determined in advance. A setting unit that sets a quantization parameter when larger than the threshold value to a value larger than the quantization parameter when the ratio of the determination blocks determined as the specific region within the predetermined processing unit is equal to or less than the threshold value;
6. The image encoding device according to claim 1, further comprising a quantization unit that quantizes the residual coefficient using a quantization value set by the setting unit. - 入力画像を符号化する画像符号化方法であって、
前記入力画像に含まれる複数の画素からなる判定ブロック毎に、当該判定ブロックが文字又は線画を含む特定領域であるか否かを判定し、
複数の変換処理単位の中から適応的に選択された変換処理単位で、前記判定ブロックの直交変換を選択的に実行することで、残差係数を出力し、
前記直交変換の選択的な実行では、
前記判定ブロックが前記特定領域であると判定された場合、常に4×4画素のブロックサイズに設定された変換処理単位毎に、前記判定ブロックの直交変換を選択的に行う
画像符号化方法。
An image encoding method for encoding an input image, comprising:
For each determination block consisting of a plurality of pixels included in the input image, determine whether the determination block is a specific region including a character or a line drawing,
By selectively executing orthogonal transformation of the determination block in a transformation processing unit adaptively selected from a plurality of transformation processing units, a residual coefficient is output,
In the selective execution of the orthogonal transform,
An image encoding method for selectively performing orthogonal transform of the determination block for each transform processing unit always set to a block size of 4 × 4 pixels when it is determined that the determination block is the specific region.
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