CN106657945A - Nonlinear segmented gamma correction implementation method - Google Patents
Nonlinear segmented gamma correction implementation method Download PDFInfo
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- CN106657945A CN106657945A CN201611270167.5A CN201611270167A CN106657945A CN 106657945 A CN106657945 A CN 106657945A CN 201611270167 A CN201611270167 A CN 201611270167A CN 106657945 A CN106657945 A CN 106657945A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
- H04N23/10—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from different wavelengths
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- 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
- G09G3/2003—Display of colours
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- 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
- G09G2320/0271—Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping
- G09G2320/0276—Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
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- General Physics & Mathematics (AREA)
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- Signal Processing (AREA)
- Picture Signal Circuits (AREA)
- Processing Of Color Television Signals (AREA)
- Facsimile Image Signal Circuits (AREA)
Abstract
The invention discloses a nonlinear segmented gamma correction implementation method, which comprises the following steps of linearly converting an RGB color coding mode of each pixel in an image sensor with a pixel matrix into a corresponding YUV chromaticity domain coding mode; respectively reserving pixel values which are corresponding to a channel Y before pixel pre-compensation for all pixels in the same row in the pixel matrix, and merging pixel values which are corresponding to a channel U and a channel V of adjacent pixel points before pre-compensation when odd-even pairing is carried out on the adjacent points in pairs, namely the pixel values which are corresponding to the channel U and the channel V before pre-compensation are the same; and dividing a section of the pixel value into multiple segments, making each segment utilize linear computation in a computation process and only computing the pixel value which is corresponding to the merged channels U and V before pre-compensation once to obtain pixel values which are corresponding to each channel Y, channel U and channel V after pre-compensation finally.
Description
Technical field
The present invention relates to semiconductor integrated circuit manufacturing technology field, more particularly to a kind of optimization method of chip hardware,
More specifically, a kind of gamma correction Hardware Implementation of non-linear piecewise.
Background technology
The opto-electronic conversion of almost all of CRT display devices, photographic film and many Electrofaxs is special in real world
Property is all nonlinear.Relation (for example, the output voltage of electron camera between the output and input of these non-linear components
With the relation of luminous intensity in scene, the intensity of the light of CRT transmittings and the relation of input voltage) can be with a power function come table
Show, its general type is：
Output=(input) γ
γ in formula is the index of power function, and it is used for weighing the transfer characteristic of non-linear components.This characteristic be referred to as power-
Rule (power-law) transfer characteristic.By convention, " input " and " output " all zoom between 0～1.Wherein, 0 black appliances are represented
Flat, 1 represents the maximum level of color component.For specific part, people can measure the letter between its input and output
Number relation, so as to find out γ values.
Actual picture system is made from multiple components, and several non-linear components are might have in these parts.Such as
Really all parts have the transfer characteristic of power function, then the transmission function of whole system is exactly a power function, its index
γ is equal to the product of the g of all single parts.If whole γ=1 of picture system, export just linear with input.This
Just mean the intensity ratio in two regions of the intensity ratio rate of any two image-region and original scene in reproduced image
Rate is identical, this target that seemingly picture system is pursued：Truly reproduce original scene.But actual conditions are not exclusively these
Sample.
When this reproduced picture is under " bright light environments ", that is, the brightness in other white objects and white portion in image
Point the almost identical environment of brightness under when watching, the system of γ=1 can make image look like " original scene " equally really.
Can be more preferable but some images watch obtained effect under " dark surrounds " sometimes, show a film and just belong to projector slide
In such case.In this case, γ values are not equal to 1 and have been generally acknowledged that g＆raquo；1.5, the visual angle system of people is seen
Scene just look like be " original scene ".According to this viewpoint, the γ values of projector slide are just designed as 1.5 or so, rather than
1.Also a kind of environment is referred to as " dim ambient " of intermediate climate, this environment just as other things in room it can be seen that
But it is more darker than the brightness of white portion in image.See that the environment of TV and the environment of computer floor just belong to such case.At this
In the case of kind, it is generally recognized that reproducing image needs γ ＆raquo；1.25 just can look like " original scene ".Divided according to above
Analysis, in order to watch " original scene " that gamma (γ) correction can be added where appropriate under various circumstances.
Gamma correction is exactly that the gamma curve to image enters edlin, to carry out the side of non-linear tone editor to image
Method, detects the dark parts and light-colored part in picture signal, and makes both ratio increases, so as to improve picture contrast effect
Really.
Human visual system (Human Visual System, abbreviation HVS) human visual system only has 3 kinds of cone cells
Response curve be nonlinear, it is possible to use values of powers function representation, commonly referred to as gamma curve, as shown in Figure 1.
ValueOut=ValueIn1/gamma
Gamma (gamma curve) is a kind of special tint ramp, and when Gamma values are equal to 1, curve is and coordinate
Axle straight line at 45 °, represents that input brightness and output brightness have identical density function this when.Gamma values higher than 1
Will cause to export brightening, the Gamma values less than 1 will cause output to darken.
In principle the visually-perceptible demand of the mankind is to be input into and export ratio close in 1.Set in input, output
This is a fairly common and important concept in standby.But in image processing system, due to display, scanning
The nonlinear response reason of the input-output equipment such as instrument, printer, it may appear that the image of reality output has deviation in brightness, and
Gamma curve correction is exactly come this method for perceiving deviation of remedial frames by certain method.
Generally, when the value for Gamma corrections is more than 1, the bloom part of image is compressed and shadow part
It is expanded, when the value of Gamma corrections is less than 1, the bloom part of image is expanded and shadow part is compressed, Gamma corrections
It is generally used for the details (as shown in Figure 2) of smooth extension shadow.
It is briefly described as follows the primary structure and principle of gamma correction of the prior art：
Hypothesis color depth is 10bit (correspondence 0～1024), has the pixel that value is 789 in image, then to this
Pixel A carries out Gamma corrections and has to carry out following steps：
Step S1：Normalized, by pixel value【0,1024】Be converted to【0,1】Between real number；Its algorithm is as follows：(i
+ 0.5)/1024 here comprising 1 division and 1 add operation, for pixel A, its corresponding normalized value is
0.770996；
Step S2：Exponentiation refers to：If gamma values are 2.3, gamma values inverse is taken, i.e.,
1/gamma=0.434782609 refers to for power；
Step S3：Precompensation, according to formula, obtains respective value of the data after pixel normalization with 1/gamma as index.
This step refers to computing comprising exponentiation above.The result pre-compensated for the A values after normalization is exactly 0.770996094^
0.434782609=0.893083881；
Step S4：Renormalization：The integer value between [0,1024] will be changed to through the real number value contravariant of precompensation.Specifically
Algorithm is：This step of f*1024-0.5 includes a multiplication and a subtraction, continues precedent, by the precompensation result of A
0.893083881 substitutes into above formula, and it is 914 finally to round and obtain corresponding pixel value after A precompensations, and this 914 is exactly finally to send
Enter the data of display.
From the above as can be seen that gamma correction operand of the prior art is very big, a large amount of floating-point fortune are used in centre
Calculate, end product is returned to integer, waste ample resources.
The content of the invention
In view of the shortcomings of the prior art, the present invention provides a kind of gamma correction of non-linear piecewise and realizes, all may be used
To be realized by the way of hardware, the optimization for chip hardware provides possibility.
For achieving the above object, technical scheme is as follows：
A kind of gamma correction implementation method of non-linear piecewise, comprises the steps：
Step S1：The rgb color coding mode of each pixel in the imageing sensor with picture element matrix is linearly turned
Corresponding YUV colourities domain coding mode is changed to, corresponding pixel value will be become before the three-channel precompensation of the rgb color
Corresponding pixel value before the precompensation of YUV colourities domain Y passages, U passages and V passages；
Step S2：Respectively all pixels in the picture element matrix with a line are retained into correspondence before Y passages pixel precompensation
Pixel value, consecutive points are carried out two-by-two odd even pairing neighbor pixel U passages and V passages precompensation before corresponding pixel
Value is merged, i.e., U passages are identical with corresponding pixel value before the precompensation of V passages；
Step S3：The interval of pixel value is divided into multistage, each section of use is linearly calculated：
PYout=a1*PYin+b1；
PUout=a2*PUin+b2；
PVout=a3*PVin+b3；
Wherein, a1 and b1 are the piecewise constants of Y passages, and PYin and PYout difference Y passages are corresponding pixel before precompensation
Corresponding pixel value after value and precompensation；
A2 and b2 are the piecewise constants of U passages, PYin and PYout difference U passages for corresponding pixel value before precompensation and
Corresponding pixel value after precompensation；
A3 and b3 are the piecewise constants of V passages, PYin and PYout difference V passages for corresponding pixel value before precompensation and
Corresponding pixel value after precompensation；
In calculating process, corresponding pixel value only calculates one before the precompensation that the U passages and V passages are merged
It is secondary, finally give corresponding pixel value after the precompensation of each the Y passages, U passages and V passages.
Preferably, in the picture element matrix it is 0～1024 that pixel value is interval, and the segments is 16.
Preferably, the segmentation of pixel value interval 0～1024 is realized as follows：
[0,4,8,12,16,20,36,52,72,84,96,128,256,384,512,768,1024]。
Preferably, in step s3, calculated using YUV422 modes.
Preferably, the gamma correction implementation method of the non-linear piecewise is all realized by the way of hardware.
From above-mentioned technical proposal as can be seen that technical scheme is quick to brightness in view of human visual system
Sense, relatively not so sensitive to colourity, the process of luminance Y channel and colourity UV passage is processed respectively, in Gamma calculating processes
In, compared to traditional by the inverted exponent arithmetic sought power-exponent function and pre-compensate for, the amount of calculation of linear transformation is reduced
A lot, particularly in hardware view, conventional adder and multiplier can realize high-performance using streamline.
Description of the drawings
Fig. 1 is gamma curve schematic diagram
Fig. 2 is gamma curve primary structure and compensation principle curve synoptic diagram
Fig. 3 is that the gamma correction Hardware Implementation flow process of the non-linear piecewise in a preferred embodiment of the present invention is shown
It is intended to
Fig. 4 is the original rgb pixel image in a preferred embodiment of the present invention, and 3 primary colors of 4 pix need to do 12
The schematic diagram of individual Gamma computings
Fig. 5 is that the RGB in a preferred embodiment of the present invention switchs to YUV colourities domain, as linear transformation, it is only necessary to group
Close the schematic diagram that circuit is achieved that
Fig. 6 is that the spatial resolution of colourity UV halves in the domain of YUV colourities 422 in a preferred embodiment of the present invention,
Brightness Y constant schematic diagram
Fig. 7 is in the domain of YUV colourities 422 in a preferred embodiment of the present invention, it is only necessary to do the signal of 8 Gamma computings
Figure
Specific embodiment
Below in conjunction with the accompanying drawings 1-6 is described in detail to the specific embodiment of the present invention.It should be understood that of the invention
Can have various changes in different examples, it is neither departed from the scope of the present invention, and it is therein explanation and be shown in
Substantially regard purposes of discussion, and be not used to limit the present invention.
It should be noted that the present invention provides a kind of gamma correction of non-linear piecewise realizing, belong to the excellent of chip hardware
Change method, it is based on the Digital Image Processing of integer arithmetic, and whole flow processs are completed in integer field, it is not necessary to floating-point operation,
In this Gamma calculating process, compared to traditional by the inverted exponent arithmetic for asking power-exponent function and precompensation, linearly
The amount of calculation of conversion is reduced a lot；Therefore, it can adopt the method that software, hardware or software and hardware combine to realize, especially
It is that, in hardware view, conventional adder and multiplier can realize high-performance using streamline.
Above-mentioned implementation method can be suitable in the imageing sensor with picture element matrix, below with the picture element matrix
Pixel value interval be described in detail for 0～1024 (certain scope is not limited to 0～1024).
In specific embodiment of the invention below, Fig. 3 is referred to, Fig. 3 is according in a preferred embodiment of the present invention
Non-linear piecewise gamma correction Hardware Implementation schematic flow sheet.As illustrated, a kind of gamma school of non-linear piecewise
Positive implementation method, comprises the steps：
Step S1：The rgb color coding mode of each pixel in the imageing sensor with picture element matrix is linearly turned
Corresponding YUV colourities domain coding mode is changed to, corresponding pixel value will be become before the three-channel precompensation of the rgb color
Corresponding pixel value before the precompensation of YUV colourities domain Y passages, U passages and V passages.
Specifically, Fig. 4 is referred to, Fig. 4 is the original rgb pixel image in a preferred embodiment of the present invention, 4 pictures
3 primary colors of plain (pix) need to make the schematic diagram of 12 Gamma computings.As illustrated, in true environment practical application, each
Pixel (pix) needs tri- Color Channels of RGB to process respectively, and (because the mankind are more sensitive to green glow, their Gamma corrections are
Number is different), i.e., for different tones are all equally processed, each pixel needs 3 sets of Gamma corrections to realize hardware, for example, with 4
As a example by pix, tradition needs 12 Gamma floating-point operations based on trichromatic process of RGB, it is seen that operand is very big, and centre is used
A large amount of floating-point operations, end product is returned to integer, wastes ample resources.
In an embodiment of the present invention, first it is that the RGB of each pixel is converted to corresponding YUV.
Step S2：Respectively all pixels in the picture element matrix with a line are retained into correspondence before Y passages pixel precompensation
Pixel value, consecutive points are carried out two-by-two odd even pairing neighbor pixel U passages and V passages precompensation before corresponding pixel
Value is merged, i.e., U passages are identical with corresponding pixel value before the precompensation of V passages.
Specifically, refer to Fig. 5 and Fig. 6, Fig. 5 are that RGB in a preferred embodiment of the present invention switchs to YUV colourities
Domain, as linear transformation, it is only necessary to the schematic diagram that combinational circuit is achieved that；Fig. 6 is according in a preferred embodiment of the present invention
The domain of YUV colourities 422 in, the spatial resolution of colourity UV halves, brightness Y constant schematic diagram.
As shown in Figure 5, it is contemplated that human visual system is, to colourity relatively not so sensitive, i.e. thing sensitive to brightness
The Neighbor Points of true picture have correlation in reality；In fact the Neighbor Points of true picture have correlation.In the present invention
Embodiment in, for each pixel is equally processed, but retain each pixel Y passages pixel precompensation before it is corresponding
Pixel value is constant, but two-by-two pixel carries out the U passages and V passages of the point of odd even pairing, i.e., two for the consecutive points of same a line
Precompensation before corresponding pixel value become the same, to the step, by taking 4 pix as an example, using technical scheme with
Afterwards, it is only necessary to which 8 Gamma computings can just realize that tradition needs 12 Gamma floating-point operations based on trichromatic process of RGB.
Step S3：The interval of pixel value is divided into multistage, each section of use is linearly calculated：
PYout=a1*PYin+b1；
PUout=a2*PUin+b2；
PVout=a3*PVin+b3；
Wherein, a1 and b1 are the piecewise constants of Y passages, and PYin and PYout difference Y passages are corresponding pixel before precompensation
Corresponding pixel value after value and precompensation；
A2 and b2 are the piecewise constants of U passages, PYin and PYout difference U passages for corresponding pixel value before precompensation and
Corresponding pixel value after precompensation；
A3 and b3 are the piecewise constants of V passages, PYin and PYout difference V passages for corresponding pixel value before precompensation and
Corresponding pixel value after precompensation；
In calculating process, corresponding pixel value is only calculated once before the precompensation that U passages and V passages are merged, most
Corresponding pixel value after the precompensation of each Y passages, U passages and V passages is obtained eventually.
Fig. 7 is referred to, Fig. 7 is in the domain of YUV colourities 422 in a preferred embodiment of the present invention, it is only necessary to be 8 Gamma
The schematic diagram of linear operation.Specifically, as illustrated, or with picture element matrix pixel value interval as 0～1024, segments
As a example by 16 sections, the processing mode following (certainly, segments is not limited to 16 sections, and per section of separation also can adjust) of integer field：
Segment lookup first：The segmentation of pixel value interval 0～1024 is realized as follows：
16 sections of [0,4,8,12,16,20,36,52,72,84,96,128,256,384,512,768,1024], this 16 sections simultaneously
Mean allocation, at first, two neighboring pixel value interval is shorter, two pixel values intervals of rear adjacent just compared with
It is long.
Then each section of use linearly calculates out=a*in+b；A and b is piecewise constant；
For example, corresponding pixel value is in=789 before the precompensation of V passages, and it is real in the present invention between 768～896
In applying example, using corresponding a3 and b3, it is out=914 that can be calculated corresponding pixel value after the precompensation of V passages.
Thus, it will be seen that being linear Gamma computings in embodiments of the present invention in Gamma calculating processes, compare
In traditional by the inverted exponent arithmetic sought power-exponent function and pre-compensate for, the amount of calculation of linear transformation is reduced a lot.
Only embodiments of the invention above, embodiment is simultaneously not used to limit the scope of patent protection of the present invention, therefore
The equivalent structure change that every specification and accompanying drawing content with the present invention is made, should be included in the same manner the protection of the present invention
In the range of.
Claims (6)
1. the gamma correction implementation method of a kind of non-linear piecewise, it is characterised in that comprise the steps：
Step S1：Rgb color coding mode linear transformation by each pixel in the imageing sensor with picture element matrix is
Corresponding YUV colourities domain coding mode, will become YUV colors by corresponding pixel value before the three-channel precompensation of the rgb color
Corresponding pixel value before the precompensation of degree domain Y passages, U passages and V passages；
Step S2：Respectively all pixels in the picture element matrix with a line are retained into corresponding picture before Y passages pixel precompensation
Element value, consecutive points is carried out two-by-two corresponding pixel value before the U passages of odd even pairing neighbor pixel and the precompensation of V passages and is added
To merge, i.e., U passages are identical with corresponding pixel value before the precompensation of V passages；
Step S3：The interval of pixel value is divided into multistage, each section of use is linearly calculated：
PYout=a1*PYin+b1；
PUout=a2*PUin+b2；
PVout=a3*PVin+b3；
Wherein, a1 and b1 are the piecewise constants of Y passages, PYin and PYout difference Y passages for corresponding pixel value before precompensation and
Corresponding pixel value after precompensation；
A2 and b2 are the piecewise constants of U passages, and PYin and PYout difference U passages are corresponding pixel value before precompensation and pre- benefit
Corresponding pixel value after repaying；
A3 and b3 are the piecewise constants of V passages, and PYin and PYout difference V passages are corresponding pixel value before precompensation and pre- benefit
Corresponding pixel value after repaying；
In calculating process, corresponding pixel value is only calculated once before the precompensation that the U passages and V passages are merged, most
Corresponding pixel value after the precompensation of each the Y passages, U passages and V passages is obtained eventually.
2. the gamma correction implementation method of non-linear piecewise according to claim 1, it is characterised in that in the picture element matrix
Pixel value it is interval be 0～1024, the segments is 16.
3. the gamma correction implementation method of non-linear piecewise according to claim 2, it is characterised in that the pixel value is interval
0～1024 segmentation is realized as follows：
[0,4,8,12,16,20,36,52,72,84,96,128,256,384,512,768,1024]。
4. according to claim 1,2 or 3 non-linear piecewise gamma correction implementation method, it is characterised in that in step S3
In, calculated using YUV422 modes.
5. the gamma correction implementation method of non-linear piecewise according to claim 1, it is characterised in that the non-linear piecewise
Gamma correction implementation method realized by the way of hardware.
6. the gamma correction implementation method of non-linear piecewise according to claim 1, it is characterised in that step S1 passes through
Combinational circuit is realized.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN108989819A (en) * | 2017-06-03 | 2018-12-11 | 上海天荷电子信息有限公司 | Each mode uses the data compression method and device of respectively corresponding color space |
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| US20020041707A1 (en) * | 2000-04-07 | 2002-04-11 | Newman David A. | Real-time color correction of digitally recorded video |
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