Classifications

• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T3/00—Geometric image transformations in the plane of the image
  • G06T3/40—Scaling of whole images or parts thereof, e.g. expanding or contracting
  • G06T3/4015—Image demosaicing, e.g. colour filter arrays [CFA] or Bayer patterns
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G5/00—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators
  • G09G5/02—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators characterised by the way in which colour is displayed
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G5/00—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators
  • G09G5/36—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators characterised by the display of a graphic pattern, e.g. using an all-points-addressable [APA] memory
  • G09G5/39—Control of the bit-mapped memory
  • G09G5/395—Arrangements specially adapted for transferring the contents of the bit-mapped memory to the screen
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2320/00—Control of display operating conditions
  • G09G2320/02—Improving the quality of display appearance
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2340/00—Aspects of display data processing
  • G09G2340/04—Changes in size, position or resolution of an image
  • G09G2340/0407—Resolution change, inclusive of the use of different resolutions for different screen areas
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2340/00—Aspects of display data processing
  • G09G2340/04—Changes in size, position or resolution of an image
  • G09G2340/0407—Resolution change, inclusive of the use of different resolutions for different screen areas
  • G09G2340/0414—Vertical resolution change
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2340/00—Aspects of display data processing
  • G09G2340/04—Changes in size, position or resolution of an image
  • G09G2340/0407—Resolution change, inclusive of the use of different resolutions for different screen areas
  • G09G2340/0421—Horizontal resolution change
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2340/00—Aspects of display data processing
  • G09G2340/04—Changes in size, position or resolution of an image
  • G09G2340/0407—Resolution change, inclusive of the use of different resolutions for different screen areas
  • G09G2340/0428—Gradation resolution change
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2340/00—Aspects of display data processing
  • G09G2340/04—Changes in size, position or resolution of an image
  • G09G2340/0457—Improvement of perceived resolution by subpixel rendering
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/2007—Display of intermediate tones
  • G09G3/2059—Display of intermediate tones using error diffusion
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/2007—Display of intermediate tones
  • G09G3/2074—Display of intermediate tones using sub-pixels

Definitions

• Embodiments of the present invention relate to the field of .displaying high resolution images on displays with lower resolution, where the displays use a triad arrangement to display the R, G, and B or other components of the image.
• This triad arrangement is common in direct view LCD displays, for example, and in such an arrangement, a single pixel is composed of 3 side-by-side subpixels .
• Each subpixel controls only one of the three primaries (i.e., R, G and B) and is, in turn, usually controlled solely by the primaries of .the digital image representation.
• the high-resolution image may be available in memory, or may be available directly from an algorithm (vector graphics, some font designs, and computer graphics) .
• the most commonly used method for displaying high-resolution images on a lower resolution display is to sample the pixels 2 of the high-resolution image 4 down to the resolution of the low-resolution display 6, as shown in Figure 1. Then, the R, G, B values of each . downsampled color pixel 8 are mapped to the separate R> G, B elements 10, 12 and 14 of each display pixel 16. These R, G, B elements 10, 12 and 14 of a display pixel are also referred to as subpixels. Because the display device does not allow overlapping color elements, the subpixels can only take on one of the three R, G, or B colors, however, the color's amplitude can be varied throughout the entire greyscale range (e.g., 0-255) .
• the subpixels usually have a 1:3 aspect ratio (width:height) , so that the resulting pixel 16 is square.
• the subsampling/mapping techniques do not consider the fact that the display's R, G, and B subpixels are spatially displaced; in fact they are assumed to be overlapping in the same manner as they are in the high-resolution image as shown in Figure 1. This type of sampling may be referred to as sub-sampling or traditional sub-sampling.
• the pixels of the high-resolution image 4 are shown as three slightly offset stacked squares 8 to indicate their RGB values are associated for the same spatial position (i.e., pixel).
• One display pixel 16, consisting of one each of the R, G and B subpixels 10, 12 and 14 is shown as part of the lower-resolution triad display 6 in Figure 1 using dark lines. Other display pixels are shown with lighter dotted lines.
• the high-resolution image has 3x more resolution than the display (in. both horizontal and vertical dimensions) . Since this direct subsampling technique causes aliasing artifacts, various methods are used such as averaging the neighboring unsampled pixels in with the sampled pixel.
• achromatic image as defined in this specification and claims has no visible color variation. This achromatic condition can occur when an image contains only one layer or color channel, or when an image has multiple layers or color channels, but each color layer is identical thereby yielding a single color image.
• luminance 17 refers to the achromatic contact of the viewed image
• chrominance 19 refers to the color content, which is processed by the visual system as isoluminant modulations from red to green, and from blue to yellow.
• the color difference signals R-G and B-Y of video are rough approximations to these modulations.
• the bandwidth of the chromatic frequency response is 1/2 that of the luminance frequency response.
• the bandwidth of the blue-yellow modulation response is even less, down to about 1/3 of the luminance.
• Sampling which comprises mapping of color elements from different image pixels to the subpixels of a display pixel triad, as shown in Figure 2, may be referred to as sub-pixel sampling.
• the sine function resulting from convolving the high-resolution source image with a rect equal to- the subpixel spacing is shown as a dashed curve 24, which has higher bandwidth.
• This is the limit imposed by the display considering that the subpixels are rect in one-dimension.
• the subpixels can display luminance information, but not chromatic information. In fact, any chromatic information in this region is aliased.
• the triad i.e., display
• the black & white fonts are typically preprocessed, as shown in Figure 5.
• the standard pre-processing includes hinting, which refers to the centering of the font strokes on the center of the pixel, i.e., a font-stroke specific phase shift. This is usually followed by low-pass filtering, also referred to as greyscale antialiasing.
• CSFs visual frequency responses
• the luminance CSF 30 has been mapped from units of cy/deg to the display pixel domain (assuming a viewing distance of 1280 pixels) . It is shown as the solid line 30 that has a maximum frequency near 1.5 cy/pixel (display pixel), and is bandpass in shape with a peak near 0.2 cy/pixel triad.
• the R:G CSF 32 is shown as the dashed line, that is lowpass with a maximum frequency near 0.5 cy/pixel.
• the B:Y modulation CSF 34 is shown as the dashed-dotted LPF curve with a similar maximum frequency as the R.-G CSF, but with lower maximum response.
• the range between the cutoff frequencies of the chrominance CSF 32 and 34 and the luminance CSF 30 is the region where we can allow chromatic aliasing in order to improve luminance bandwidth.
• Figure 6 (a) also shows an idealized image power spectra 36 as a l/f function, appearing in the figure as a straight line with a slope of -1 (since the figure is using log axes) .
• This spectrum will repeat at the sampling frequency. These repeats are shown for the pixel 38 and the subpixel 40 sampling rates for the horizontal direction. The one occurring at lower frequencies 38 is due to the pixel sampling, and the one at the higher frequencies 40 is due to the subpixel sampling. Note that the shapes change since we are plotting on a log frequency axis . The frequencies of these repeat spectra that extend to the lower frequencies below Nyquist are referred to as aliasing. The leftmost one is chromatic aliasing 38 since it is due to the pixel sampling rate, while the luminance aliasing 40 occurs at higher frequencies because it is related to the higher sub-pixel sampling rate.
• the present invention has been contrived, based on the aforementioned characteristics of the spatial frequency responses of the human visual system, in other words, on the fact that the luminance CSF has a higher cutoff frequency than the chrominance CSF.
• a low-resolution image is formed by separating a higher-resolution image into a luminance data and a chrominance data so as to carry out suitable sampling and filtering for each of the luminance data and the chrominance data, then by combing the luminance data and the chrominance data after the sampling.
• the chrominance data traditional sub-sampling is carried out to avoid chromatic aliasing, while sub-pixel sampling is performed for the luminance data to improve resolution of luminance component.
• respective R, G, and ,B values of R, G, and B subpixels 10, 12-, and 14 in one display pixel 16 reflect to respective R, G, and B values of color pixel 8 (i.e., 11) of an image 4 having a high resolution by sub-sampling shown in Figure 1.
• the respective R, G, and B values of the subpixels 10, 12 and 14 are not identical with the respective R, G, and B values of the color pixel 8(11) .
• sub-pixel sampling shown in Figure 2 is carried out so that the respective R, G, and B values of the subpixel 10, 12 and 14 reflect luminance components of the color pixels 11, 13 and 15.
• Embodiments of the present invention comprise methods and systems that rely less on filtering and its assumption of linearity and are capable of working on input color images. These embodiments are capable of directly removing low frequency chromatic artifacts after they are caused by sub-pixel sampling. This is achieved by generating a LPF version of the chromatic content of the image which is added to the luminance and chromatic aliasing versions. This is done by making use of color dominans other than additive, primary color domains (i.e., RGB) to remove the color artifacts caused by the sub-pixel sampling. In practice, only the lower frequency chromatic artifacts need to be cancelled, since the high frequency ones cannot be seen due to the lower bandwidth of the chromatic CSFs, as shown .in Figure 6(a) .
• the methods and systems of the present invention may be used in obtaining higher resolution luminance signals with no visibility of chromatic aliasing, when the display is viewed no closer than designed specifications. These techniques do not need the assumption that the source image is text or that the images are achromatic.
• Embodiments of the present invention convert a higher-resolution image to a lower-resolution image with reduced errors caused by the sub-sampling processes.
• the higher-resolution image is not in a format which allows separation of luminance and chrominance data
• the image is converted to such a format .
• Many opponent color domains are acceptable.
• the opponent color domain image is split thereby separating the luminance channel from the chrominance channels thereby allowing for separate processing.
• the luminance channel is then converted to an additive color domain (ACD) , such as RGB, and the ACD luminance image is sub-pixel sampled to preserve luminance data while reducing resolution.
• ACD additive color domain
• SPS sub-pixel sampled
• OCD opponent color domain
• the SPS chrominance channels produced by this split are then high-pass filtered to remove low-frequency artifacts produced during sub-pixel sampling.
• the SPS luminance channel is typically not modified to preserve original luminance data .
• the chrominance channels from the original image are low-pass filtered and then Sub-sampled to provide the chrominance data for the lower-resolution image.
• These low-pass filtered chrominance channels are then combined with the high-pass filtered, sub-pixel sampled chrominance channels created from the original luminance channel.
• These combined chrominance channels are also combined with the SPS luminance channel to form a reduced-error, lower-resolution image, generally in an opponent color domain. This error-reduced, lower-resolution image may then be converted to an additive color domain or some other color domain compatible with the desired application.
• Figure 1 is a diagram showing traditional image sampling for displays with a triad pixel configuration
• Figure 2 is a diagram showing sub-pixel image sampling for a display with a triad pixel configuration
• Figure 3 is a graph showing idealized CSFs mapped to a digital frequency plane
• Figure 4 is a graph showing an analysis of the pixel
• Figure 5 shows typical pre-processing techniques
• Figure 6(a) is a graph showing an analysis using 1/f-power spectra repeated at pixel sampling and sub-pixel sampling frequencies
• Figure 6 (b) is a graph showing an analysis using 1/f-power spectra repeated at pixel sampling and sub-pixel sampling frequencies with improvements due to pre-processing
• Figure 7 is a block diagram showing a known use of a visual model
• FIG. 8 is a flow diagram showing embodiments of the present invention.
• FIG. 9 is a flow diagram showing specific embodiments of the present invention.
• Figure 10 is graph showing signals retained by embodiments of the present invention.
• the software in which the features of the embodiments of the present invention is embodied in such a manner that the software is stored in a medium readable for a computer.
• Examples of such media include communication media (optical fibers, wireless communication lines, or the like) used in a computer network (LAN, WAN such as the Internet or the like, and the wireless communication network) system, besides recording media such as information storing means (semiconductor memories, floppy discs, hard disks, or the like) and optical storing means (CD-ROM, DVD, or the like) .
• information storing means semiconductor memories, floppy discs, hard disks, or the like
• optical storing means CD-ROM, DVD, or the like
• achromatic refers to an image that has no visible color variation.
• An achromatic image may be an image that contains only one layer or color channel, or an image that has multiple layers or color channels, but each color layer is identical thereby yielding a single color image.
• Embodiments of the present invention may also be described and claimed with reference to "YCrCb" images or domains, "opponent color” domains, images or channels, or “color difference” domains, images or channels.
• These terms as used in this specification and related claims, may refer to any form of multiple component image domain with channels which comprise at least one distinct luminance channel and chrominance channels including, but not limited to YCrCb, LAB, YUV, and YIQ domains.
• Embodiments of the present invention may be used to convert higher-resolution images to lower-resolution images with fewer visible errors in the converted image. While these embodiments are typically used in conjunction with a display device to convert images which have a higher resolution than the display down to a resolution that is usable by the display, other applications are applicable .
• Images converted with embodiments of the present invention may exist in a variety of formats. When these formats are not compatible with the processes of embodiments of the present invention, the images may be converted .to . a compatible format prior .to processing and • may be converted back, when necessary, after processing.
• Embodiments of the present invention may be explained in reference to Figure 8 which depicts a diagram summarizing exemplary embodiments.
• This process 70 begins with an image that exists in an opponent color domain (OCD) such as a YCrCb, LAB, YUV, YIQ or similar domain.
• OCD opponent color domain
• ACD additive color domain
• Some embodiments include steps to convert images into a compatible format prior to processing.
• the image is "split" (step 74) to provide for separate processing of luminance and chrominance channels.
• “Splitting” (step 74) may comprise sampling or filtering of the original OCD image 72 or other methods of isolating luminance and chrominance data from the original image 72. Splitting may also comprise image conversion.
• the initial luminance channel 76 is converted (step 78) to an ACD luminance image, such as a RGB image. This is done to enable sampling of the luminance image in the format or domain in which it will eventually, be . displayed.
• ACD luminance image such as a RGB image.
• sub-pixel sampling ..(step..80) is performed on the image to improve the resolution of the resulting lower-resolution image. In this manner, the luminance data from each successive pixel in the original higher-resolution image is assigned to each corresponding sub-pixel in the lower-resolution image.
• this SPS luminance image is converted (step 82) to an OCD image which may be referred to as a SPS-OCD luminance image.
• This conversion is performed to allow for further splitting (step 84) of the SPS luminance image into distinct luminance and chrominance channels .
• the SPS luminance channel 86 is typically left undisturbed until subsequent combination (step 88) with other channels.
• the SPS chrominance channels 90 & 92 are filtered prior to further combination.
• These SPS chrominance channels 90 & 92 may be divided into a Red-to-Green channel 90 and a Blue-to-Yellow channel 92. These channels typically comprise the Cr and Cb channels of a YCrCb image, the "a" and “b” channels of a LAB image, the U and V channels of a YUV image, the I and Q channels of a YIQ image or similar channels of other color spaces or domains. These chrominance channels 90 & 92 are high-pass filtered (steps 94 & 96) to remove low frequency artifacts which occur during sub-pixel sampling.
• high-pass filtering may be performed via an unsharp mask method.
• the unsharp mask may use a low-pass kernel.
• the original image is processed with the low-pass kernel yielding a low-pass version of the image.
• This low-pass version is subsequently subtracted from the original unfiltered image while preserving the image's mean value.
• Successful embodiments have used a Gaussian low-pass kernel with a sigma of about 0.3 pixels to about 0.8 pixels. A sigma value of 0.6 pixels is thought to be particularly successful and results in a cut-off in the frequency domain of about 0.168 cycles/pixel. This gives a good unsharp-mask filter.
• the derivation for the Gaussian kernel is given below.
• ⁇ in the space domain corresponds • to l/ ⁇ 2 ⁇ in frequency domain (units of cycles/pixel) .
• This relation can be used to help determine the cut-off frequency of the filter given its ⁇ , or, conversely, to determine the spatial ⁇ for the unsharp mask given a frequency, which may be guided by CSF models.
• a 2-dimensional Gaussian function used in some embodiments is given as :
• a successful embodiment of the present invention has employed ' a Gaussian unsharp mask filter implemented with a kernel of size 3x3, with a value for sigma chosen as 0.6 resulting in a cut-off frequency of the low-pass filter around 0.2 cycles/pix.
• Other embodiments of the present invention may use high-pass filters which are equivalent to the inverse CSFs for the respective opponent color channels. These CSFs may be mapped from the domain of cy/deg (where they are modeled) to the digital domain of cy/pix.
• the actual mapping rocess takes into account the viewing distance, and allows for customization for different applications, having particular display resolutions in pixels/mm and different expected or intended viewing distances.
• chromatic artifacts will be invisible when viewed no closer than the designed viewing distance. However, the luminance resolution will be improved.
• This filtering (steps 94 & 96) may be performed for all chrominance channels 90 & 92 or for selected channels based on the amount or intensity of artifacts introduced in the particular sampling process or based on some other criteria .
• Low-pass filtering (steps 102 & 104) of the original OCD chrominance channels 98 & 100 may take place simultaneously with processing in the luminance pathway 105 or may take place at some other time.
• Low-pass filtering (steps 102 & 104) of the OCD chrominance channels is performed to remove substantial chromatic frequencies above the display pixel Nyquist frequency. Accordingly, these channels may be sub-sampled (steps 101 & 103) in a traditional manner by a factor of 1:3 without the generation of chromatic aliasing in the chromatic pathways 110.
• the segregated channels may be combined. Combination of chromatic channels will vary depending on the color domain used.
• the high-pass filtered, sub-pixel sampled Blue-to-Yellow (HPFSPS-B/Y) chromatic channel 97 is combined (step 106) with the low-pass filtered, traditionally sub-sampled Blue-to-Yellow (LPFSS-B/Y) chromatic channel 109 to form a single high-low filtered (HLF) B/Y chromatic channel 111.
• the high pass filtered, sub-pixel sampled Red-to- Green (HPFSPS-R/G) channel 95 is also combined (step 108) with the low-pass filtered, traditionally sub-sampled Red-to-Green (LPFSS-R/G) channel 107 to form a single high-low filtered (HLF) R/G channel 114.
• T h e combined HLF chrominance channels 111 & 114 may be further combined (step 88) with SPS luminance channel 86 to form a lower-resolution OCD image 116.
• Lower-resolution OCD image 116 may then be converted or otherwise transformed to other image formats or domains as required for various purposes .
• the methods and systems of these embodiments provide a lower-resolution image with fewer visible chromatic artifacts .
• the above embodiments may be modified in various manners.
• the low-pass filtering (steps 102 & 104) of the chrominance channels 98 & 100 may be omitted.
• each step of the luminance pathway 105 with respect to the luminance channel 76, while omitting each step of the chromatic pathway 110 and the steps 106 and 108 with respect to the chrominance channels 98 & 100, so as to combine the SPS luminance channel 86, and the HPFSPS-R/G channel 95 and HPFSPS-B/Y channel 97. In this way, it is possible to form the lower- resolution image 116.
• specific exemplary embodiments of the present invention may be explained. This particular embodiment may be used to process higher-resolution RGB images for display on a lower-resolution display device.
• a higher-resolution RGB image 120 may be optionally pre-processed (step 122) according to specific needs of a user or application.
• Pre-processing may comprise hinting, types of low-pass filtering or some other processing techniques. Pre-processing (step 122) may also be bypassed altogether.
• the RGB may be converted (step 124) to an opponent color domain image such as a LAB, YCrCb, YIQ,- YUV or other image .domain. In this example, the LAB image domain is used. Once converted to this domain, the image may be split (step 126) into the separate L, a, and b channels of the domain for separate processing of the channels. In this manner, the chrominance and luminance channels may be processed separately.
• the "L” channel 127 is then converted (step 128) back to the RGB domain so that it may be sampled in its final display format.
• This conversion may comprise simple copying of the L layer or channel into three identical R, G, and B layers. A single layer may also be used, however, the actual conversion method will depend on the color transform chosen.
• Sub-pixel sampling (step 130) is then performed on this RGB luminance image to preserve the horizontal luminance resolution of the original RGB image 120.
• the sampled image is again converted (step 132) to an opponent color domain, such as LAB.
• This sampled LAB image is split (step 134) to isolate the luminance and chrominance channels for further processing of the chrominance channels.
• the luminance channel 136 is typically not processed to preserve the original luminance data.
• the chrominance channels 150 & 152 of the sub-pixel sampled and split image are high-pass filtered (steps 146 & 148) to remove low-frequency chromatic .aliasing that occurs during., sub-pixel sampling.
• this high-pass filtering may be performed with an unsharp-mask filter using a Gaussian low-pass kernel.
• the chrominance channels are filtered yielding a low-pass filtered chrominance image which is subtracted from the SPS-RGB chrominance image to create a "high-pass” filtered (HPF)SPS chrominance image or channel 147&149.
• High-pass filtering (steps 146 & 148) is typically performed on both the "a" and "b" channels, but may be performed on only one channel when conditions permit .
• Low-pass filtering (steps 138 & 140) of the original "a" and “b” chrominance channels 154 & 156 may take place simultaneously with processing of the "L" channel or may take place at some other time.
• Low-pass filtering (steps 138 & 140) of the "a" and “b” chrominance channels is performed to remove substantial chromatic frequencies above the display pixel Nyquist frequency.
• these channels may be sub-sampled (steps 142 & 144) in a traditional manner by a factor of 1:3 without the generation of chromatic aliasing.
• the high-pass filtered luminance "a" channel 147 is ..combined ..(step 160) with the .sub-sampled, low-pass filtered "a” channel 143 to form a processed "a” channel 164.
• the high-pass filtered luminance "b" channel 149 is combined (step 158) with the sub-sampled, low-pass filtered "b” channel 145 to form a processed "b” channel 162.
• These chrominance channels 162 & 164 are then combined (step 166) with the SPS luminance channel 136 to form an error-reduce, lower-resolution LAB image 168.
• This error-reduced image may be converted (step 170) to an RGB domain to produce an error-reduced; lower-resolution RGB image 172 which may be output to a display or other device.
• FIG. 10 shows the signals retained relative to the luminance CSF 180 and chromatic CSF 182.
• the chromatic signals preserved include the high-pass region 184, which is undetectable to the chromatic CSF, as well as the low-pass region 186, which contains the useful chromatic content of the image. Ideally, the frequencies missing from this low-pass chromatic 186 will not be visible to the observer because of the RG and BY CSF's limited bandwidths .
• the HPF chromatic signal 184 is the chromatic aliasing that carries valid luminance information. Note that since the low frequency chromatic information is retained, this technique will work with color images.
• Figure 10 shows no overlap, between these two chromatic signals, but depending on the actual filters used, overlap may be possible.
• Other embodiments may include the use of filters that allow for overlap of the high-pass 184 and low-pass 186 chromatic signals shown in Figure 10. Overlap can allow for more chromatic bandwidth at the expense of chromatic aliasing.

Landscapes

• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Theoretical Computer Science (AREA)
• Computer Hardware Design (AREA)
• Image Processing (AREA)
• Control Of Indicators Other Than Cathode Ray Tubes (AREA)
• Color Image Communication Systems (AREA)
• Color Television Systems (AREA)
• Editing Of Facsimile Originals (AREA)
• Facsimile Image Signal Circuits (AREA)

Applications Claiming Priority (7)

Publications (1)

Family

ID=27419197

Family Applications (1)

Country Status (5)

Families Citing this family (13)

Family Cites Families (3)

• 2001
  • 2001-12-12 EP EP01270858A patent/EP1350221A2/de not_active Withdrawn
  • 2001-12-12 CN CN 01822601 patent/CN1267882C/zh not_active Expired - Fee Related
  • 2001-12-12 WO PCT/JP2001/010915 patent/WO2002048960A2/en not_active Application Discontinuation
  • 2001-12-12 TW TW90130880A patent/TW558899B/zh active
  • 2001-12-12 JP JP2002550598A patent/JP2004524729A/ja not_active Withdrawn

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events