CN102497490B - System and method for realizing image high dynamic range compression - Google Patents
System and method for realizing image high dynamic range compression Download PDFInfo
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- CN102497490B CN102497490B CN201110422639.5A CN201110422639A CN102497490B CN 102497490 B CN102497490 B CN 102497490B CN 201110422639 A CN201110422639 A CN 201110422639A CN 102497490 B CN102497490 B CN 102497490B
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Abstract
The invention relates to a system for realizing image high dynamic range compression. The system comprises a primary image input unit, an exposure area calculation unit, a comparison unit, a correction unit, and a compressed image output unit. The invention also relates to a method for realizing the image high dynamic range compression. By adopting the system and the method for realizing the image high dynamic range compression, the problems of damage to a normal exposure area, Halo existing at the edge and over loss of image contrast in the method are effectively solved; the contrast of the normal exposure area is reserved, at the same time, the visibility of the under exposure area and the exposure area is improved; the system and method not only are directly applied in an overall high dynamic compression method, but also can be applied in the brightness (lighting layer) compression in a partial high dynamic compression manner; and besides, the complexity of the operation in the invention is extremely low, so that real time process is facilitated, the process is quick and efficient, the working performance is stable and reliable, and the scope of the application is broad.
Description
Technical field
The present invention relates to digital picture/field of video processing, particularly digital picture/Video compression technical field, specifically refers to a kind of system and method thereof that realizes image high dynamic range compression.
Background technology
The high-high brightness of piece image or scene and the ratio of minimum brightness are called the dynamic range (Dynamic Range) of this image or scene.Along with the number of bits (bit wide) of image/video harvester constantly increases, and synthetic high dynamic range (High Dynamic Range of later stage, HDR) development of image/video technology, high dynamic range compression is also widely used in the every field such as collection, processing and reproduction of digital picture/video.Corresponding with high dynamic range, be low-dynamic range (Low Dynamic Range, LDR).Common low dynamic device has: traditional monitor, printer, low-bit width imageing sensor etc.The dynamic range that can show or record due to these equipment is much smaller than the dynamic range of high dynamic range images/video.If therefore want normally to show or record the image/video of high dynamic range on low-dynamic range equipment, just need to compress high dynamic range images/video.
Current high dynamic range compression method can be divided into two large classes according to the difference of its final mapping curve generating: global map, local mapping.So-called global map carries out the mapping from HDR to LDR according to certain algorithm, makes identical input pixel value be mapped to identical output pixel value, and identical its mapping method of input pixel is also identical.Similarly, so-called local mapping carries out the mapping from HDR to LDR according to certain algorithm, makes identical input pixel value be mapped to different output pixel values, and identical its mapping method of input pixel is not identical.
The Gamma correction of the method that represents of global map described in document < < Digital Image Processing 3rd Edition > >, based on histogrammic rectification etc.The advantage of this class mapping method is to be convenient to realize, and computational complexity is extremely low; Shortcoming is to be easy to some part of original image to cause overcompression, damages region of normal exposure and reduces picture contrast etc.
The method that represents of local mapping is described in document < < Fast bilateral filtering for the display of high-dynamic-range images > >, it is divided into texture image and light image by input high-dynamics image by two-sided filter, texture image has kept the detailed information of original image, and light image has been preserved the illumination information of scene, to light image compress after and texture image be merged into the output image after final compression.The local mapping method of this class can retain the details of original image preferably, but computational complexity is far longer than global map algorithm, and its final effect is directly limited to the scale size of filter.If filter yardstick is too small, can not correctly estimate the illumination information of scene, also just cannot correctly isolate texture image, compression effectiveness is poor.If filter yardstick is excessive, not only computational complexity increases, and can introduce obvious halation (Halo) phenomenon.
Meanwhile, in the high Dynamic Compression of prior art, no matter be Global Algorithm or local algorithm, when brightness (illumination layer) is compressed, common method has two kinds.Utilize a statistic histogram for original image/video, after it is reduced, carry out maximum, minimum value mapping; A kind of is to utilize predefine mapping curve (similar Gamma correction) to shine upon.These two class methods are not all considered the region of normal exposure of original image/video, therefore may cause excess compression to cause contrast to decline to a great extent or the under-exposure of image/video or overexposure region are adjusted to deficiency the region of normal exposure of image/video, directly affect compression effectiveness.
Summary of the invention
The object of the invention is to have overcome above-mentioned shortcoming of the prior art, provide a kind of can effectively solve damage that region of normal exposure, border occur that halation (Halo) and picture contrast lose that excessive problem, processing procedure quickness and high efficiency, algorithm complex are lower, system and method thereof that stable and reliable working performance, the scope of application realize image high dynamic range compression comparatively widely.
In order to realize above-mentioned object, system and the method thereof that realizes image high dynamic range compression of the present invention is as follows:
This realizes the system of image high dynamic range compression, and its main feature is that described system comprises:
Original image input unit, for obtaining pending image;
Exposure area computing unit, is connected with described original image input unit, for calculating and divide the exposure area of pending image;
Comparing unit, is connected with exposure area computing unit with described original image input unit respectively, for exposure area that each pixel of pending image and this exposure area computing unit are divided relatively and select corresponding calibration curve;
Correcting unit, is connected with described comparing unit, for proofreading and correct and produce new pixel value according to corresponding calibration curve; And
Compressed images output unit, is connected with described correcting unit, after pixel value is mapped to suitable color space, exports.
This realizes exposure area in the system of image high dynamic range compression for by analyzing the pixel value of pending image the region of pending image being cut apart according to the difference of depth of exposure.
This exposure area of realizing in the system of image high dynamic range compression comprises overexposure region, under-exposure region, region of normal exposure and zone line.
This is realized in the system of image high dynamic range compression and also comprising:
Illumination/details separator, is connected with described original image input unit, for isolate illumination layer image and texture layer image from original image, and described illumination layer image is delivered in described exposure area computing unit;
Fusion device, illumination layer image after the correction of the correcting unit output described in receiving and the texture layer image of illumination/details separator output, and illumination layer image and texture layer image after proofreading and correct are merged to rear generation compressed images, and export described compressed images output unit to.
This realizes the method for image high dynamic range compression, and its main feature is that described method comprises the following steps:
(1) original image of input is analyzed, calculated and divide the exposure area of pending image;
(2) each pixel of pending image and described exposure area are compared, and select corresponding calibration curve;
(3), for each pixel, according to corresponding calibration curve, proofread and correct and produce new pixel value;
(4) described new pixel value is mapped to suitable color space output.
The exposure area of dividing pending image is analyzed and calculated to this original image to input of realizing in the method for image high dynamic range compression, comprises the following steps:
(11) monochrome information of original image is analyzed, and marked off existing region of normal exposure, under-exposure region, overexposure region and zone line;
(12) calculate and obtain luminance threshold, the luminance threshold in overexposure region and the luminance threshold of region of normal exposure in under-exposure region.
Existing region of normal exposure, under-exposure region, overexposure region and zone line are analyzed and marked off to this monochrome information to original image realizing in the method for image high dynamic range compression, comprises the following steps:
(111) original image calibration curve according to following formula representative in brightness is done to γ
1the mapping of > 1, the map image y after being proofreaied and correct
1:
And original image calibration curve according to following formula representative in brightness is done to γ
2the mapping of < 1, the map image y after being proofreaied and correct
2:
Wherein, x is the original image of input;
(112) calculate respectively original image x and the map image y of input
1and y
2in the gradient information of each pixel;
(113) successively by map image y
1the gradient corresponding with each pixel of the original image x inputting is the poor amplitude of variation Δ y that obtains
1x, if this amplitude of variation Δ y
1x is greater than the first threshold th of systemic presupposition
1, include this pixel in under-exposure region; If this amplitude of variation Δ y
1x is less than the 3rd threshold value th of systemic presupposition
3, include this pixel in region of normal exposure; Otherwise include this pixel in zone line;
(114) successively by map image y
2the gradient corresponding with each pixel of the original image x inputting is the poor amplitude of variation Δ y that obtains
2x, if this amplitude of variation Δ y
2x is greater than the Second Threshold th of systemic presupposition
2, include this pixel in overexposure region; If this amplitude of variation Δ y
2x is less than the 3rd threshold value th of systemic presupposition
3, include this pixel in region of normal exposure; Otherwise include this pixel in zone line.
This realizes the γ in the method for image high dynamic range compression
1value is 2.2.
This realizes the γ in the method for image high dynamic range compression
2value is 0.4545.
This is realized the calculating in the method for image high dynamic range compression and obtains luminance threshold, the luminance threshold in overexposure region and the luminance threshold of region of normal exposure in under-exposure region, comprises the following steps:
(121) count the brightness average m of each pixel in under-exposure region
1with variance v
1, and by m
1+ λ v
1as the luminance threshold in under-exposure region, wherein λ is for adjusting the factor;
(122) count the brightness average m of each pixel in overexposure region
2with variance v
2, and by m
2-λ v
2luminance threshold as overexposure region;
(123) count the brightness average m of each pixel of region of normal exposure
3with variance v
3, and by m
3+ λ v
3as the higher limit of the luminance threshold of region of normal exposure, by m
3-λ v
3lower limit as the luminance threshold of region of normal exposure.
This is realized, in the method for image high dynamic range compression, each pixel of pending image and described exposure area is compared and select corresponding calibration curve, comprises the following steps:
(21), if described pixel is positioned at under-exposure region, select the calibration curve of the brightness value of this pixel of lifting;
(22), if described pixel is positioned at overexposure region, select the calibration curve of the brightness value of this pixel of inhibition;
(23), if described pixel is positioned at region of normal exposure, select to keep the brightness value of this pixel constant or finely tune the calibration curve of this pixel brightness value;
(24), if described pixel is positioned at zone line, select default zone line gamma correction curve.
This calibration curve of realizing the brightness value of the lifting pixel in the method for image high dynamic range compression is the curve of following formula representative:
y＝x
1/γ；
Wherein, γ=2.2, x is the pixel brightness value before proofreading and correct, y is the pixel brightness value after proofreading and correct.
This calibration curve of realizing the brightness value of the inhibition pixel in the method for image high dynamic range compression is the curve of following formula representative:
y＝x
1/γ；
Wherein, γ=0.4545, x is the pixel brightness value before proofreading and correct, y is the pixel brightness value after proofreading and correct.
This realizes the brightness value of this pixel of maintenance in the method for image high dynamic range compression calibration curve constant or that finely tune this pixel brightness value is the curve of following formula representative:
y＝x；
Wherein, x is the pixel brightness value before proofreading and correct, and y is the pixel brightness value after proofreading and correct.
This zone line gamma correction curve of realizing in the method for image high dynamic range compression is the curve of following formula representative:
y＝kx+b；
Wherein, x is the pixel brightness value before proofreading and correct, and y is the pixel brightness value after proofreading and correct,
x
2for the minimum pixel brightness value in the Yi Ce region, overexposure region of zone line, y
2for map intensity values corresponding to this pixel value, x
1for the maximum pixel brightness value in the Yi Ce region, under-exposure region of zone line, y
1for map intensity values corresponding to this pixel value.
This pixel value by new of realizing in the method for image high dynamic range compression is mapped to suitable color space output, is specially:
According to the mapping relations of new pixel brightness value and original pixels brightness value, the brightness value of new pixel is mapped on R, G, B component.
This realizes new pixel brightness value in the method for image high dynamic range compression and the mapping relations of original pixels brightness value are:
Wherein, R
oUT, G
oUTand B
oUTbe respectively R, G, the B component of new pixel brightness value, R
iN, G
iN, B
iNbe respectively R, G, the B component of original pixels brightness value.
This step (1) realizing in the method for image high dynamic range compression is further comprising the steps of before:
(0) from the image of required compression, isolate illumination layer image and texture layer image, and the original image using described illumination layer image as input;
Described step (4) is further comprising the steps of afterwards:
(5) the illumination layer image of exporting after processing and texture layer image are merged to rear generation compressed images output.
The system that realizes image high dynamic range compression and the method thereof of this invention have been adopted, due to wherein by input picture is analyzed, divide normal exposure and under-exposure region, promote under-exposure regional luminance, keep region of normal exposure brightness, thereby efficiently solve and in high dynamic range compression method, damage region of normal exposure, border occurs that halation (Halo) and picture contrast lose excessive problem, and when retaining region of normal exposure contrast, promoted the observability in under-exposure region and overexposure region, not only can directly apply to overall high Dynamic Compression, and can apply to brightness (illumination layer) compression in local high Dynamic Compression, simultaneously, computational complexity of the present invention is extremely low, be convenient to real-time processing, processing procedure quickness and high efficiency, stable and reliable working performance, the scope of application is comparatively extensive.
Accompanying drawing explanation
Fig. 1 is the embodiment schematic diagram of realizing the system of image high dynamic range compression of the present invention.
Fig. 2 is the another kind of embodiment schematic diagram of realizing the system of image high dynamic range compression of the present invention.
Fig. 3 is the processing procedure schematic diagram of realizing the method for image high dynamic range compression of the present invention.
Fig. 4 is the exposure area distribution schematic diagram that has under-exposure region, zone line, region of normal exposure and overexposure region in the present invention time.
Fig. 5 is the exposure area distribution schematic diagram that has region of normal exposure, zone line and overexposure region in the present invention.
Fig. 6 is the exposure area distribution schematic diagram that has under-exposure region, zone line and region of normal exposure in the present invention.
Fig. 7 is the exposure area distribution schematic diagram that only has under-exposure region in the present invention.
Fig. 8 is the exposure area distribution schematic diagram that only has overexposure region in the present invention.
Embodiment
In order more clearly to understand technology contents of the present invention, especially exemplified by following examples, describe in detail.
Refer to shown in Fig. 1 and Fig. 2, this realizes the system of image high dynamic range compression, comprising:
(1) original image input unit 300, for obtaining pending image;
(2) exposure area computing unit 301, are connected, for calculating and divide the exposure area of pending image with described original image input unit 300; Described exposure area is by analyzing the pixel value of pending image the region of pending image being cut apart according to the difference of depth of exposure; This exposure area can comprise overexposure region, under-exposure region, region of normal exposure and zone line;
(3) comparing unit 302, be connected with exposure area computing unit 301 with described original image input unit 300 respectively, for exposure area that each pixel of pending image and this exposure area computing unit are divided relatively and select corresponding calibration curve;
(4) correcting unit 303, are connected, for proofreading and correct and produce new pixel value according to corresponding calibration curve with described comparing unit 302; And
(5) compressed images output unit 304, are connected with described correcting unit 303, after pixel value is mapped to suitable color space, export.
As the system that realizes image local high dynamic range compression, comprising:
(1) original image input unit 10, for obtaining pending image;
(2) exposure area computing unit 18, are connected, for calculating and divide the exposure area of pending image with described original image input unit 10; Described exposure area is by analyzing the pixel value of pending image the region of pending image being cut apart according to the difference of depth of exposure; This exposure area can comprise overexposure region, under-exposure region, region of normal exposure and zone line;
(3) comparing unit 20, be connected with exposure area computing unit 18 with described original image input unit 10 respectively, for exposure area that each pixel of pending image and this exposure area computing unit are divided relatively and select corresponding calibration curve;
(4) correcting unit 22, are connected, for proofreading and correct and produce new pixel value according to corresponding calibration curve with described comparing unit 302; And
(5) compressed images output unit 26, are connected with described correcting unit 303, after pixel value is mapped to suitable color space, export.
(6) illumination/details separator 12, are connected with described original image input unit 10, for isolate illumination layer image and texture layer image from original image, and described illumination layer image 14 delivered in described exposure area computing unit 18;
(7) fusion device 24, illumination layer image 14 after the correction of correcting unit 22 outputs described in receiving and the texture layer image 16 of illumination/details separator 12 outputs, and the illumination layer image 14 after proofreading and correct is merged to rear generation compressed images with texture layer image 16, and export described compressed images output unit 26 to.
In the middle of reality is used, Fig. 1 is a kind of high dynamic press device provided by the invention as the structural representation of an execution mode of overall high dynamic compression independently, wherein, this device comprises: original image input unit 300, exposure area computing unit 301, comparing unit 302, correcting unit 303, compressed images output unit 304.
Original image input unit 300 is for obtaining pending image.
Exposure area computing unit 301 is for calculating and divide the exposure area of pending image.Described exposure area refers to by analyzing the pixel value of pending image, according to the difference of depth of exposure, pending image is divided into overexposure region, under-exposure region, region of normal exposure and zone line.Above region may be with a kind of existence the in five kinds of forms of Fig. 4 to Fig. 8 in pending image.
Comparing unit 302 for exposure areas that each pixel of pending image and 301 is divided relatively and select corresponding calibration curve.
Correcting unit 303 is for proofreading and correct and produce new pixel value according to corresponding calibration curve.
Compressed images output unit 304 is exported after pixel value is mapped to suitable color space.
Refer to again shown in Fig. 2, it is a kind of high dynamic press device provided by the invention as the structural representation of an execution mode of illumination layer compression in the high dynamic compression in part, and wherein, this device comprises: original image input unit 10, illumination/details separator 12, illumination layer image 14, texture layer image 16, exposure area computing unit 18, comparing unit 20, correcting unit 22, fusion device 24, compressed images output unit 26.
Original image input unit 10 is for obtaining pending image.
Illumination/details separator 12 is for isolating illumination layer image 14 and texture layer image 16 from original image.In specific embodiment, illumination/details separator can be Gaussian filter can be also other form as the filter retaining with border.
Exposure area computing unit 18 is for calculating and divide the exposure area of pending image.Described exposure area refers to by analyzing the pixel value of illumination layer image, according to the difference of depth of exposure, illumination layer image is divided into overexposure region, under-exposure region, region of normal exposure and zone line.Above region may be with a kind of existence the in five kinds of forms of Fig. 4 to Fig. 8 in pending image.
Comparing unit 20 for exposure areas that each pixel of illumination layer image and 18 is divided relatively and select corresponding calibration curve.
Correcting unit 22 is for proofreading and correct and produce new illumination layer pixel value according to corresponding calibration curve.Illumination layer image after correction and texture layer image produce compressed images through fusion device 24.
Compressed images output unit 26 is exported after pixel value is mapped to suitable color space.
Refer to shown in Fig. 3, this realizes the method for image high dynamic range compression again, comprising following steps:
(1) original image of input is analyzed, is calculated and divide the exposure area of pending image, comprise the following steps:
(a) monochrome information of original image is analyzed, and is marked off existing region of normal exposure, under-exposure region, overexposure region and zone line, comprise the following steps:
(i) original image calibration curve according to following formula representative in brightness is done to γ
1the mapping of > 1, the map image y after being proofreaied and correct
1:
And original image calibration curve according to following formula representative in brightness is done to γ
2the mapping of < 1, the map image y after being proofreaied and correct
2:
Wherein, x is the original image of input; This γ
1value is 22, γ
2value is 0.4545;
(ii) calculate respectively original image x and the map image y of input
1and y
2in the gradient information of each pixel;
(iii) successively by map image y
1the gradient corresponding with each pixel of the original image x inputting is the poor amplitude of variation Δ y that obtains
1x, if this amplitude of variation Δ y
1x is greater than the first threshold th of systemic presupposition
1, include this pixel in under-exposure region; If this amplitude of variation Δ y
1x is less than the 3rd threshold value th of systemic presupposition
3, include this pixel in region of normal exposure; Otherwise include this pixel in zone line;
(iv) successively by map image y
2the gradient corresponding with each pixel of the original image x inputting is the poor amplitude of variation Δ y that obtains
2x, if this amplitude of variation Δ y
2x is greater than the Second Threshold th of systemic presupposition
2, include this pixel in overexposure region; If this amplitude of variation Δ y
2x is less than the 3rd threshold value th of systemic presupposition
3, include this pixel in region of normal exposure; Otherwise include this pixel in zone line;
(b) calculate and obtain luminance threshold, the luminance threshold in overexposure region and the luminance threshold of region of normal exposure in under-exposure region, comprise the following steps:
(i) count the brightness average m of each pixel in under-exposure region
1with variance v
1, and by m
1+ λ v
1as the luminance threshold in under-exposure region, wherein λ is for adjusting the factor;
(ii) count the brightness average m of each pixel in overexposure region
2with variance v
2, and by m
2-λ v
2luminance threshold as overexposure region;
(iii) count the brightness average m of each pixel of region of normal exposure
3with variance v
3, and by m
3+ λ v
3as the higher limit of the luminance threshold of region of normal exposure, by m
3-λ v
3lower limit as the luminance threshold of region of normal exposure;
(2) each pixel of pending image and described exposure area are compared, and select corresponding calibration curve, comprise the following steps:
(a), if described pixel is positioned at under-exposure region, select the calibration curve of the brightness value of this pixel of lifting; The calibration curve of the brightness value of this lifting pixel is the curve of following formula representative:
y＝x
1/γ；
Wherein, γ=2.2, x is the pixel brightness value before proofreading and correct, y is the pixel brightness value after proofreading and correct;
(b), if described pixel is positioned at overexposure region, select the calibration curve of the brightness value of this pixel of inhibition; The calibration curve of the brightness value of this inhibition pixel is the curve of following formula representative:
y＝x
1/γ；
Wherein, γ=0.4545, x is the pixel brightness value before proofreading and correct, y is the pixel brightness value after proofreading and correct;
(c), if described pixel is positioned at region of normal exposure, select to keep the brightness value of this pixel constant or finely tune the calibration curve of this pixel brightness value; This keeps the brightness value of this pixel calibration curve constant or that finely tune this pixel brightness value is the curve of following formula representative:
y＝x；
Wherein, x is the pixel brightness value before proofreading and correct, and y is the pixel brightness value after proofreading and correct;
(d), if described pixel is positioned at zone line, select default zone line gamma correction curve; This zone line gamma correction curve is the curve of following formula representative:
y＝kx+b；
Wherein, x is the pixel brightness value before proofreading and correct, and y is the pixel brightness value after proofreading and correct,
x
2for the minimum pixel brightness value in the Yi Ce region, overexposure region of zone line, y
2for map intensity values corresponding to this pixel value, x
1for the maximum pixel brightness value in the Yi Ce region, under-exposure region of zone line, y
1for map intensity values corresponding to this pixel value;
(3), for each pixel, according to corresponding calibration curve, proofread and correct and produce new pixel value;
(4) described new pixel value is mapped to suitable color space output, is specially:
According to the mapping relations of new pixel brightness value and original pixels brightness value, the brightness value of new pixel is mapped on R, G, B component, the mapping relations of the pixel brightness value that this is new and original pixels brightness value are:
Wherein, R
oUT, G
oUTand B
oUTbe respectively R, G, the B component of new pixel brightness value, R
iN, G
iN, B
iNbe respectively R, G, the B component of original pixels brightness value.
For the method that realizes image local high dynamic range compression, step wherein (1) is further comprising the steps of before:
(0) from the image of required compression, isolate illumination layer image and texture layer image, and the original image using described illumination layer image as input;
Described step (4) is further comprising the steps of afterwards:
(5) the illumination layer image of exporting after processing and texture layer image are merged to rear generation compressed images output.
In the middle of reality is used, the present invention is achieved by the following technical solutions:
This quick high dynamic range compression method, by input picture is analyzed, divide normal exposure, under-exposure or overexposure and zone line, the brightness and the contrast that when adjusting the brightness in under-exposure or overexposure region and contrast, keep region of normal exposure are compressed brightness and the contrast of zone line simultaneously.
Due to general a kind of in region of normal exposure, under-exposure or overexposure region and zone line or all form of piece image.So-called region of normal exposure, refers to and can on LDR equipment, normally show or posting field, there will not be dark or excessively bright situation.And so-called under-exposure or overexposure region refers to and cross dark or excessively bright region when showing or recording on LDR equipment.Zone line is between the region between the above two.In order to adjust under-exposure or overexposure region in the contrast that guarantees region of normal exposure simultaneously, improve compression effectiveness, we adopt the thinking of dividing based on exposure area to carry out high dynamic range compression.
The thought of method of the present invention is summarized as follows:
First the monochrome information of original image or illumination layer is analyzed, marked off the region of normal exposure that may exist, under-exposure or overexposure region and zone line.The one or more threshold values within the scope of corresponding input picture valid pixel are all distinguished in region of normal exposure and under-exposure or overexposure region, and the region between region of normal exposure threshold value and under-exposure or overexposure region threshold value is called zone line.Possible threshold value distributes as shown in Fig. 4 to Fig. 8, when region of normal exposure is positioned at input picture valid pixel scope intermediate pixel, as shown in Figure 4, be followed successively by from left to right: under-exposure region (0～L1), zone line (L1～L2), region of normal exposure (L2～L3), zone line (L3～L4), overexposure region (L4～1).When region of normal exposure is positioned at the low pixel region of input picture valid pixel scope, as shown in Figure 5, be followed successively by from left to right: region of normal exposure (0～L3), zone line (L3～L4), overexposure region (L4～1).When region of normal exposure is positioned at the high pixel region of input picture valid pixel scope, as shown in Figure 6, be followed successively by from left to right: under-exposure region (0～L1), zone line (L1～L2), region of normal exposure (L2～1).When region of normal exposure does not exist, as shown in Figure 7,8, entire image is all under-exposure region or overexposure region.
The method of analyzing and dividing various exposure areas has a lot, as by histogram analysis, by gradient analysis etc.Except above cited method, no matter finally adopt which kind of method, all do not deviate from basic thought of the present invention and do not exceed protection scope of the present invention.
Complete after the exposure area division of original image or illumination layer, start each region to shine upon.First for region of normal exposure, shine upon, for the mapping principle in this region, be that not lose overall contrast be prerequisite, thus the maximum after the normalization of this region input pixel and minimum value remain unchanged or finely tune after be mapped to maximum and the minimum value after the normalization of output pixel.The computational methods of the mapping curve in this region have a lot, can be also S curve etc. for slope is fixed as a curve of 1.Except above cited method, no matter finally adopt which kind of method, all do not deviate from basic thought of the present invention and do not exceed protection scope of the present invention.
Secondly under-exposure region is shone upon, for the mapping principle in this region be the brightness that promotes dark portion region be prerequisite, so this region is mapped to value after the normalization of the output pixel value after with respect to the normalization of input pixel and has lifting by a relatively large margin.The computational methods of the mapping curve in this region have a lot, can by predefined correction curve also can by current pixel and around adjacent pixel values dynamic calculation obtain etc.Except above cited method, no matter finally adopt which kind of method, all do not deviate from basic thought of the present invention and do not exceed protection scope of the present invention.
Then overexposure region is shone upon, for the mapping principle in this region be the brightness that reduced bright area be prerequisite, so this region is mapped to value after the normalization of the output pixel value after with respect to the normalization of input pixel and has inhibition by a relatively large margin.The computational methods of the mapping curve in this region have a lot, can by predefined correction curve also can by current pixel and around adjacent pixel values dynamic calculation obtain etc.Except above cited method, no matter finally adopt which kind of method, all do not deviate from basic thought of the present invention and do not exceed protection scope of the present invention.
Finally zone line is shone upon, for the mapping principle in this region be the overall contrast that reduces this region be prerequisite, so there are inhibition by a relatively large margin in this region maximum of difference after with respect to the normalization of input pixel of being mapped to maximum after the normalization of output pixel and minimum value and the missionary society of minimum value.The computational methods of the mapping curve in this region have a lot, can also can be by the under-exposure region after mapping or the input of overexposure region and region of normal exposure and output pixel dynamic calculation etc. by predefined correction curve.Except above cited method, no matter finally adopt which kind of method, all do not deviate from basic thought of the present invention and do not exceed protection scope of the present invention.
So far, high dynamic range compression method of the present invention finishes, if be applied to the illumination layer compression in Local compression method, the illumination layer after this method compression is exported final compression result after being combined with texture layer; If be applied to global compaction method, compaction algorithms finishes.
Flow chart as an execution mode of high dynamic range compression method of the present invention, specifically comprises the steps:
(1) calculate and obtain under-exposure regional luminance threshold value, overexposure region luminance threshold and the region of normal exposure luminance threshold that may exist that is applied to present image.
(2) from original image, obtain a pending pixel, as current pixel.
(3) calculate the brightness of current pixel.It should be noted that, exposure area based on brightness is divided and mapping is a specific embodiment of this patent, in specific implementation, no matter for exposure area and corresponding threshold value, how to divide and to shine upon, no matter finally adopt which kind of method, all do not deviate from basic thought of the present invention and do not exceed protection scope of the present invention; Similarly, no matter finally adopt which kind of method to calculate brightness, all do not deviate from basic thought of the present invention and do not exceed protection scope of the present invention.
(4) current pixel brightness and the under-exposure regional luminance threshold value counting are compared, if current pixel is positioned at under-exposure region, promote this pixel brightness value.This pixel intensity output valve can by predefined correction curve also can by current pixel and around adjacent pixel values dynamic calculation obtain etc.In the present embodiment, adopt y=x
1/ γcorrection curve calculate brightness after the rectification in under-exposure region, γ=2.2, x is for correcting preceding pixel brightness value, y is pixel brightness value after correcting.No matter finally adopt which kind of method to calculate brightness, all do not deviate from basic thought of the present invention and do not exceed protection scope of the present invention;
If current pixel is positioned at overexposure region, suppress this pixel brightness value.This pixel intensity output valve can by predefined correction curve also can by current pixel and around adjacent pixel values dynamic calculation obtain etc.In the present embodiment, adopt y=x
1/ γcorrection curve calculate brightness after the rectification in overexposure region, γ=0.4545, x is for correcting preceding pixel brightness value, y is pixel brightness value after correcting.No matter finally adopt which kind of method to calculate brightness, all do not deviate from basic thought of the present invention and do not exceed protection scope of the present invention;
If current pixel is positioned at region of normal exposure, remains unchanged or finely tune this pixel brightness value.The computational methods of this pixel intensity output valve have a lot, can be also S curve etc. for slope is fixed as a curve of 1.In the present embodiment, adopt the correction curve of y=x to calculate brightness after the rectification of region of normal exposure, x is for correcting preceding pixel brightness value, and y is pixel brightness value after correcting.No matter finally adopt which kind of method, all do not deviate from basic thought of the present invention and do not exceed protection scope of the present invention;
If current pixel is positioned at zone line, in the present embodiment, adopt the correction curve of y=kx+b to calculate brightness after the rectification of zone line, x is for correcting preceding pixel brightness value, and y is pixel brightness value after correcting,
X wherein
2for the minimum pixel brightness value of zone line right side area, y
2for map intensity values corresponding to this pixel value, x
1for the maximum pixel brightness value of zone line left field, y
1for map intensity values corresponding to this pixel value.No matter finally adopt which kind of method, all do not deviate from basic thought of the present invention and do not exceed protection scope of the present invention.
(5) relation with input pixel brightness value according to output pixel brightness value, is mapped to R, G, B component by the brightness value of output pixel.Mapping relations in the present embodiment are
R wherein
oUT, G
oUTand B
oUTbe respectively R, G, the B component of output pixel, R
iN, G
iN, B
iNbe respectively R, G, the B component of input pixel.By the brightness value of pixel be mapped to R, G, B component has a lot of methods, in specific implementation, except above cited method, no matter finally adopts which kind of method, all do not deviate from basic thought of the present invention and do not exceed protection scope of the present invention.
Described step (1) comprises following steps:
(11) entire image is done respectively in brightness to the y=x of γ=2.2 and γ=0.4545
1/ γmapping, output is respectively y
1and y
2.
(12) difference calculating input image x and mapping y
1and y
2the gradient information of each pixel.The method of compute gradient has a lot, no matter finally adopts which kind of method, does not all deviate from basic thought of the present invention and does not exceed protection scope of the present invention.
(13) successively by y
1the gradient corresponding with each pixel of input picture x is poor Δ y
1x, when its amplitude of variation is greater than threshold value th
1time, this pixel is included in and owed the region of exposing to the sun.Count the average m in the region of owing to expose to the sun
1with variance v
1, calculate m
1+ λ v
1as under-exposure regional luminance threshold value, wherein λ is for adjusting the factor.
Similarly, successively by y
2the gradient corresponding with each pixel of input picture x is poor Δ y
2x, when its amplitude of variation is greater than threshold value th
2time, include this pixel in overexposure region.Count the average m in overexposure region
2with variance v
2, calculate m
2-λ v
2as overexposure region luminance threshold.As Δ y
1x and Δ y
2the amplitude of variation of x is less than threshold value th
3time, include this pixel in region of normal exposure.Count the average m of region of normal exposure
3with variance v
3, calculate m
3+ λ v
3, m
3-λ v
3bound as region of normal exposure luminance threshold.The transition in region of normal exposure and under-exposure region and region of normal exposure and overexposure region is called zone line.
The above-mentioned system that realizes image high dynamic range compression and method thereof have been adopted, due to wherein by input picture is analyzed, divide normal exposure and under-exposure region, promote under-exposure regional luminance, keep region of normal exposure brightness, thereby efficiently solve and in high dynamic range compression method, damage region of normal exposure, border occurs that halation (Halo) and picture contrast lose excessive problem, and when retaining region of normal exposure contrast, promoted the observability in under-exposure region and overexposure region, not only can directly apply to overall high Dynamic Compression, and can apply to brightness (illumination layer) compression in local high Dynamic Compression, simultaneously, computational complexity of the present invention is extremely low, be convenient to real-time processing, processing procedure quickness and high efficiency, stable and reliable working performance, the scope of application is comparatively extensive.
In this specification, the present invention is described with reference to its specific embodiment.But, still can make various modifications and conversion obviously and not deviate from the spirit and scope of the present invention.Therefore, specification and accompanying drawing are regarded in an illustrative, rather than a restrictive.
Claims (11)
1. a method that realizes image high dynamic range compression, is characterized in that, described method comprises the following steps:
(1) original image of input is analyzed, calculated and divide the exposure area of pending image; Comprise the following steps:
(11) monochrome information of original image is analyzed, and marked off existing region of normal exposure, under-exposure region, overexposure region and zone line; Comprise the following steps:
(111) original image calibration curve according to following formula representative in brightness is done to γ
1the mapping of > 1, the map image y after being proofreaied and correct
1:
And original image calibration curve according to following formula representative in brightness is done to γ
2the mapping of < 1, the map image y after being proofreaied and correct
2:
Wherein, x is the original image of input;
(112) calculate respectively original image x and the map image y of input
1and y
2in the gradient information of each pixel;
(113) successively by map image y
1the gradient corresponding with each pixel of the original image x inputting is the poor amplitude of variation Δ y that obtains
1x, if this amplitude of variation Δ y
1x is greater than the first threshold th of systemic presupposition
1, include this pixel in under-exposure region; If this amplitude of variation Δ y
1x is less than the 3rd threshold value th of systemic presupposition
3, include this pixel in region of normal exposure; Otherwise include this pixel in zone line;
(114) successively by map image y
2the gradient corresponding with each pixel of the original image x inputting is the poor amplitude of variation Δ y that obtains
2x, if this amplitude of variation Δ y
2x is greater than the Second Threshold th of systemic presupposition
2, include this pixel in overexposure region; If this amplitude of variation Δ y
2x is less than the 3rd threshold value th of systemic presupposition
3, include this pixel in region of normal exposure; Otherwise include this pixel in zone line;
(12) calculate and obtain luminance threshold, the luminance threshold in overexposure region and the luminance threshold of region of normal exposure in under-exposure region;
(2) each pixel of pending image and described exposure area are compared, and select corresponding calibration curve;
(3), for each pixel, according to corresponding calibration curve, proofread and correct and produce new pixel value;
(4) described new pixel value is mapped to suitable color space output, is specially:
According to the mapping relations of new pixel brightness value and original pixels brightness value, the brightness value of new pixel is mapped on R, G, B component.
2. the method that realizes image high dynamic range compression according to claim 1, is characterized in that, described γ
1value is 2.2.
3. the method that realizes image high dynamic range compression according to claim 1, is characterized in that, described γ
2value is 0.4545.
4. the method that realizes image high dynamic range compression according to claim 1, it is characterized in that, described calculating is also obtained luminance threshold, the luminance threshold in overexposure region and the luminance threshold of region of normal exposure in under-exposure region, comprises the following steps:
(121) count the brightness average m of each pixel in under-exposure region
1with variance v
1, and by m
1+ λ v
1as the luminance threshold in under-exposure region, wherein λ is for adjusting the factor;
(122) count the brightness average m of each pixel in overexposure region
2with variance v
2, and by m
2-λ v
2luminance threshold as overexposure region;
(123) count the brightness average m of each pixel of region of normal exposure
3with variance v
3, and by m
3+ λ v
3as the higher limit of the luminance threshold of region of normal exposure, by m
3-λ v
3lower limit as the luminance threshold of region of normal exposure.
5. the method that realizes image high dynamic range compression according to claim 1, is characterized in that, described each pixel of pending image and described exposure area is compared and select corresponding calibration curve, comprises the following steps:
(21), if described pixel is positioned at under-exposure region, select the calibration curve of the brightness value of this pixel of lifting;
(22), if described pixel is positioned at overexposure region, select the calibration curve of the brightness value of this pixel of inhibition;
(23), if described pixel is positioned at region of normal exposure, select to keep the brightness value of this pixel constant or finely tune the calibration curve of this pixel brightness value;
(24), if described pixel is positioned at zone line, select default zone line gamma correction curve.
6. the method that realizes image high dynamic range compression according to claim 5, is characterized in that, the calibration curve of the brightness value of described lifting pixel is the curve of following formula representative:
y＝x
1/γ；
Wherein, γ=2.2, x is the pixel brightness value before proofreading and correct, y is the pixel brightness value after proofreading and correct.
7. the method that realizes image high dynamic range compression according to claim 5, is characterized in that, the calibration curve of the brightness value of described inhibition pixel is the curve of following formula representative:
y＝x
1/γ；
Wherein, γ=0.4545, x is the pixel brightness value before proofreading and correct, y is the pixel brightness value after proofreading and correct.
8. the method that realizes image high dynamic range compression according to claim 5, is characterized in that, the brightness value of described this pixel of maintenance calibration curve constant or that finely tune this pixel brightness value is the curve of following formula representative:
y＝x；
Wherein, x is the pixel brightness value before proofreading and correct, and y is the pixel brightness value after proofreading and correct.
9. the method that realizes image high dynamic range compression according to claim 5, is characterized in that, described zone line gamma correction curve is the curve of following formula representative:
y＝kx＋b；
Wherein, x is the pixel brightness value before proofreading and correct, and y is the pixel brightness value after proofreading and correct,
x
2for the minimum pixel brightness value in the Yi Ce region, overexposure region of zone line, y
2for map intensity values corresponding to this pixel value, x
1for the maximum pixel brightness value in the Yi Ce region, under-exposure region of zone line, y
1for map intensity values corresponding to this pixel value.
10. the method that realizes image high dynamic range compression according to claim 5, is characterized in that, described according to the mapping relations of new pixel brightness value and original pixels brightness value, and the brightness value of new pixel is mapped on R, G, B component, is specially:
Wherein, R
oUT, G
oUTand B
oUTbe respectively R, G, the B component of new pixel brightness value, R
iN, G
iN, B
iNbe respectively R, G, the B component of original pixels brightness value.
11. according to the method that realizes image high dynamic range compression described in any one in claim 1 to 10, it is characterized in that, described step (1) is further comprising the steps of before:
(0) from the image of required compression, isolate illumination layer image and texture layer image, and the original image using described illumination layer image as input;
Described step (4) is further comprising the steps of afterwards:
(5) the illumination layer image of exporting after processing and texture layer image are merged to rear generation compressed images output.
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