CN102497490A - System and method for realizing image high dynamic range compression - Google Patents

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

Realize the system and the method thereof of image high dynamic range compression

Technical field

The present invention relates to digital picture/field of video processing, particularly digital picture/video compression processing technology field specifically is meant a kind of system and method thereof that realizes the 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.Constantly increase of number of bits (bit wide) along with the image/video harvester; And synthetic HDR (High Dynamic Range of later stage; HDR) development of image/video technology, high dynamic range compression also is widely used in the every field such as collection, processing and reproduction of digital picture/video.Corresponding with HDR, be low-dynamic range (Low Dynamic Range, LDR).Common low dynamic device has: traditional monitor, printer, low-bit width imageing sensor etc.Because the dynamic range that these equipment can show or write down is much smaller than the dynamic range of high dynamic range images/video.If therefore want the normal image/video that shows or write down HDR on low-dynamic range equipment, just need compress to high dynamic range images/video.

Present high dynamic range compression method can be divided into two big types according to the difference of its final mapping curve that generates: global map, local map.So-called global map is promptly carried out the mapping from HDR to LDR according to certain algorithm, makes identical input pixel value be mapped to identical output pixel value, and promptly identical its mapping method of input pixel is also identical.Similarly, so-called local map is promptly carried out the mapping from HDR to LDR according to certain algorithm, makes identical input pixel value be mapped to different output pixel values, and promptly identical its mapping method of input pixel is inequality.

Gamma described in the representative method of global map such as the document " Digital Image Processing 3rd Edition " corrects, based on histogrammic rectification etc.The advantage of this type mapping method is to be convenient to realize that computational complexity is extremely low; Shortcoming is to be easy to some part of original image is caused overcompression, damages region of normal exposure and reduces picture contrast etc.

Described in the representative method of local map such as the document " Fast bilateral filtering for the display of high-dynamic-range images "; It will be imported high-dynamics image and be divided into texture image and light image through two-sided filter; Texture image has kept the detailed information of original image; And light image has been preserved the illumination information of scene, light image is compressed the back be merged into the output image after the final compression with texture image.This type local map method can keep the details of original image preferably, but computational complexity is far longer than the global map algorithm, and its final effect directly is subject to the scale size of filter.If the filter yardstick is too small, then can not correctly estimate the illumination information of scene, also just can't correctly isolate texture image, compression effectiveness is relatively poor.If the filter yardstick is excessive, not only computational complexity increases, and can introduce tangible halation (Halo) phenomenon.

Simultaneously, in the high Dynamic Compression of prior art, no matter be Global Algorithm or local algorithm, to brightness (illumination layer) when compressing, common method has two kinds.A kind of statistic histogram that utilizes original image/video carries out maximum, minimum value mapping after it is reduced; A kind of is to utilize predefine mapping curve (similar gamma is corrected) to shine upon.These two class methods are not all considered the region of normal exposure of original image/video; Therefore it is perhaps not enough to the regional adjustment of the under-exposure or overexposure of image/video to cause excess compression to cause contrast to decline to a great extent to the region of normal exposure of image/video, directly influences compression effectiveness.

Summary of the invention

The objective 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 loss 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 the image high dynamic range compression comparatively widely.

In order to realize above-mentioned purpose, the system and the method thereof of realization image high dynamic range compression of the present invention are following:

This realizes the system of image high dynamic range compression, and its main feature is that described system comprises:

The original image input unit is used to obtain pending image;

The exposure area computing unit is connected with described original image input unit, is used to calculate and divide the exposure area of pending image;

Comparing unit is connected with the exposure area computing unit with described original image input unit respectively, and the exposure area that is used for each pixel and this exposure area computing unit of pending image are divided relatively and select corresponding calibration curve;

Correcting unit is connected with described comparing unit, is used for proofreading and correct the new pixel value of generation according to corresponding calibration curve; And

The compressed images output unit is connected with described correcting unit, exports after being used for pixel value is mapped to suitable color space.

Exposure area in the system of this realization image high dynamic range compression is through the pixel value of analyzing pending image and the zone of pending image being cut apart according to the difference of depth of exposure.

Exposure area in the system of this realization image high dynamic range compression comprises overexposure zone, under-exposure zone, region of normal exposure and zone line.

Also comprise in the system of this realization image high dynamic range compression:

Illumination/details separator is connected with described original image input unit, is used for isolating illumination layer image and texture layer image from original image, and described illumination layer image is delivered in the computing unit of described exposure area;

Fusion device; Receive the texture layer image that illumination layer image and illumination/details separator after the correction of described correcting unit output are exported; And the illumination layer image after will proofreading and correct and texture layer image merge the back and produce 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 may further comprise the steps:

(1) original image of input is analyzed, calculated and divide the exposure area of pending image;

(2) each pixel and the described exposure area with pending image compares, and selects corresponding calibration curve;

(3), proofread and correct the new pixel value of generation according to corresponding calibration curve to each pixel;

(4) described new pixel value is mapped to suitable color space and output.

The exposure area of dividing pending image is analyzed and calculated to the original image to input in the method for this realization image high dynamic range compression, may further comprise the steps:

(11) monochrome information of original image is analyzed, and marked off existing region of normal exposure, under-exposure zone, overexposure zone and zone line;

(12) calculate and obtain the luminance threshold in under-exposure zone, the luminance threshold in overexposure zone and the luminance threshold of region of normal exposure.

Existing region of normal exposure, under-exposure zone, overexposure zone and zone line are analyzed and marked off to the monochrome information to original image in the method for this realization image high dynamic range compression, may further comprise the steps:

(111) original image is γ according to the calibration curve of following formula representative in brightness₁＞1 mapping, the map image y after obtaining proofreading and correct₁:

${\mathrm{<figure-callout\; label="y"\; filenames="HDA0000121126220000031.png,HDA0000121126220000032.png"\; state="\{\{state\}\}">y</figure-callout>}}_1=x^{1/{\mathrm{\&gamma;}}_1};$

And original image is γ according to the calibration curve of following formula representative in brightness₂＜1 mapping, the map image y after obtaining proofreading and correct₂:

$y_2=x^{1/{\mathrm{\&gamma;}}_2};$

Wherein, x is the original image of input;

(112) calculate original image x and the map image y that imports respectively₁And y₂In the gradient information of each pixel;

(113) successively with map image y₁Do difference with the corresponding gradient of each pixel of the original image x that imports and obtain amplitude of variation Δ y₁If x is this amplitude of variation Δ y₁X is greater than the first threshold th of systemic presupposition₁, then include this pixel in under-exposure zone; If this amplitude of variation Δ y₁X is less than the 3rd threshold value th of systemic presupposition₃, then include this pixel in region of normal exposure; Otherwise include this pixel in zone line;

(114) successively with map image y₂Do difference with the corresponding gradient of each pixel of the original image x that imports and obtain amplitude of variation Δ y₂If x is this amplitude of variation Δ y₂X is greater than the second threshold value th of systemic presupposition₂, then include this pixel in the overexposure zone; If this amplitude of variation Δ y₂X is less than the 3rd threshold value th of systemic presupposition₃, then include this pixel in region of normal exposure; Otherwise include this pixel in zone line.

γ in the method for this realization image high dynamic range compression₁Value is 2.2.

γ in the method for this realization image high dynamic range compression₂Value is 0.4545.

Calculating in the method for this realization image high dynamic range compression is also obtained the luminance threshold in under-exposure zone, the luminance threshold in overexposure zone and the luminance threshold of region of normal exposure, may further comprise the steps:

(121) count the brightness average m of each pixel in under-exposure zone₁With variance v₁, and with m₁+ λ v₁As the luminance threshold in under-exposure zone, wherein λ is the adjustment factor;

(122) count the brightness average m of each pixel in overexposure zone₂With variance v₂, and with m₂-λ v₂Luminance threshold as the overexposure zone;

(123) count the brightness average m of each pixel of region of normal exposure₃With variance v₃, and with m₃+ λ v₃As the higher limit of the luminance threshold of region of normal exposure, with m₃-λ v₃Lower limit as the luminance threshold of region of normal exposure.

Each pixel and described exposure area with pending image in the method for this realization image high dynamic range compression compare and select corresponding calibration curve, may further comprise the steps:

(21), then select the calibration curve of the brightness value of this pixel of lifting if described pixel is positioned at under-exposure zone;

(22), then select the calibration curve of the brightness value of this pixel of inhibition if described pixel is positioned at the overexposure zone;

(23), then select to keep the brightness value of this pixel constant or finely tune the calibration curve of this pixel brightness value if described pixel is positioned at region of normal exposure;

(24), then select preset zone line gamma correction curve if described pixel is positioned at zone line.

The calibration curve of the brightness value of the lifting pixel in the method for this realization 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.

The calibration curve of the brightness value of the inhibition pixel in the method for this realization 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.

The brightness value of this pixel of maintenance in the method for this realization 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.

Zone line gamma correction curve in the method for this realization 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,x₂Be the minimum pixel brightness value in the zone of the overexposure of zone line zone one side, y₂Be the corresponding map intensity values of this pixel value, x₁Be the maximum pixel brightness value in the zone of the under-exposure regional side of zone line, y₁Be the corresponding map intensity values of this pixel value.

The pixel value with new in the method for this realization image high dynamic range compression is mapped to suitable color space and 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, the B component.

The new pixel brightness value in the method for this realization image high dynamic range compression and the mapping relations of original pixels brightness value are:

$R_{\mathrm{OUT}}=\frac{y}{x}\&times;R_{\mathrm{IN}};$

$G_{\mathrm{OUT}}=\frac{y}{x}\&times;G_{\mathrm{IN}};$

$B_{\mathrm{OUT}}=\frac{y}{x}\&times;B_{\mathrm{IN}};$

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.

Step (1) in the method for this realization 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 with the original image of described illumination layer image as input;

Described step (4) is further comprising the steps of afterwards:

(5) illumination layer image and the texture layer image exported the back be will handle and back generation compressed images and output merged.

The system and the method thereof of the realization image high dynamic range compression of this invention have been adopted, owing to, divide normal exposure and under-exposure zone wherein through input picture is analyzed; Promote under-exposure regional luminance, keep region of normal exposure brightness, thus efficiently solve damage region of normal exposure in the high dynamic range compression method, halation (Halo) and the excessive problem of picture contrast loss appear in the border; And when keeping the region of normal exposure contrast; Promote the observability in under-exposure zone and overexposure zone, not only can directly apply to overall high Dynamic Compression, and can apply to brightness (illumination layer) compression in the local high Dynamic Compression; Simultaneously; Computational complexity of the present invention is extremely low, is convenient to real-time processing, the processing procedure quickness and high efficiency; Stable and reliable working performance, the scope of application are comparatively extensive.

Description of drawings

Fig. 1 is the embodiment sketch map of the system of realization image high dynamic range compression of the present invention.

Fig. 2 is the another kind of embodiment sketch map of the system of realization image high dynamic range compression of the present invention.

Fig. 3 is the processing procedure sketch map of the method for realization image high dynamic range compression of the present invention.

There is the exposure area distribution schematic diagram in under-exposure zone, zone line, region of normal exposure and overexposure zone in Fig. 4 for time among the present invention.

Fig. 5 is the exposure area distribution schematic diagram that has region of normal exposure, zone line and overexposure zone among the present invention.

Fig. 6 is the exposure area distribution schematic diagram that has under-exposure zone, zone line and region of normal exposure among the present invention.

Fig. 7 is the exposure area distribution schematic diagram that has only under-exposure zone among the present invention.

Fig. 8 is the exposure area distribution schematic diagram that has only the overexposure zone among the present invention.

Embodiment

In order more to be expressly understood technology contents of the present invention, the special following examples of lifting specify.

See also illustrated in figures 1 and 2ly, this realizes the system of image high dynamic range compression, comprising:

(1) the originalimage input unit 300, are used to obtain pending image;

(2) the exposurearea computing unit 301, are connected with described originalimage input unit 300, are used to calculate and divide the exposure area of pending image; Described exposure area is through the pixel value of analyzing pending image and the zone of pending image being cut apart according to the difference of depth of exposure; This exposure area can comprise overexposure zone, under-exposure zone, region of normal exposure and zone line;

(3) comparingunit 302; Be connected with exposurearea computing unit 301 with described originalimage input unit 300 respectively, the exposure area that is used for each pixel and this exposure area computing unit of pending image are divided relatively and select corresponding calibration curve;

(4) correctingunit 303, are connected with described comparingunit 302, are used for proofreading and correct the new pixel value of generation according to corresponding calibration curve; And

(5) the compressedimages output unit 304, are connected with described correctingunit 303, export after being used for pixel value is mapped to suitable color space.

As the system that realizes the image local high dynamic range compression, comprising:

(1) the originalimage input unit 10, are used to obtain pending image;

(2) the exposurearea computing unit 18, are connected with described originalimage input unit 10, are used to calculate and divide the exposure area of pending image; Described exposure area is through the pixel value of analyzing pending image and the zone of pending image being cut apart according to the difference of depth of exposure; This exposure area can comprise overexposure zone, under-exposure zone, region of normal exposure and zone line;

(3) comparingunit 20, are connected with exposurearea computing unit 18 with described originalimage input unit 10 respectively, and the exposure area that is used for each pixel and this exposure area computing unit of pending image are divided relatively and select corresponding calibration curve;

(4) correctingunit 22, are connected with described comparingunit 302, are used for proofreading and correct the new pixel value of generation according to corresponding calibration curve; And

(5) the compressedimages output unit 26, are connected with described correctingunit 303, export after being used for pixel value is mapped to suitable color space.

(6) illumination/details separator 12 is connected with described originalimage input unit 10, is used for isolating illumination layer image and texture layer image from original image, and describedillumination layer image 14 is delivered in the described exposurearea computing unit 18;

(7)fusion device 24; Receiveillumination layer image 14 andtexture layer image 16 that illumination/details separator 12 is exported after the correction of described correctingunit 22 outputs; And the illumination layer image after will proofreading and correct 14 merges the back withtexture layer image 16 and produces compressed images, and exports described compressedimages output unit 26 to.

In the middle of reality is used; Fig. 1 is the independently structural representation of an execution mode of overall high dynamic compression of a kind of high dynamic compression device conduct provided by the invention, and wherein, this device comprises: originalimage input unit 300; Exposurearea computing unit 301; Comparingunit 302, correctingunit 303, compressedimages output unit 304.

Originalimage input unit 300 is used to obtain pending image.

Exposurearea computing unit 301 is used to calculate and divide the exposure area of pending image.Said exposure area is meant through analyzing the pixel value of pending image, according to the difference of depth of exposure pending image is divided into overexposure zone, under-exposure zone, region of normal exposure and zone line.Above zone maybe be with a kind of existence the in five kinds of forms of Fig. 4 to Fig. 8 in pending image.

The exposure area that comparingunit 302 is used for each pixel of pending image and 301 is divided relatively and select corresponding calibration curve.

Correctingunit 303 is used for proofreading and correct the new pixel value of generation according to corresponding calibration curve.

Compressedimages output unit 304 is exported after being used for pixel value is mapped to suitable color space.

See also shown in Figure 2ly again, it is a kind of high dynamic compression device provided by the invention as the structural representation of an execution mode of illumination layer compression in the high dynamic compression in part, wherein; This device comprises: originalimage input unit 10, illumination/details separator 12,illumination layer image 14;Texture layer image 16, exposurearea computing unit 18, comparingunit 20; Correctingunit 22,fusion device 24, compressedimages output unit 26.

Originalimage input unit 10 is used to obtain pending image.

Illumination/details separator 12 is used for isolatingillumination layer image 14 andtexture layer image 16 from original image.In specific embodiment, illumination/details separator can be that Gauss's smoothing filter also can be the filter like the boundary reservation of other form.

Exposurearea computing unit 18 is used to calculate and divide the exposure area of pending image.Said exposure area is meant through analyzing the pixel value of illumination layer image, according to the difference of depth of exposure the illumination layer image is divided into overexposure zone, under-exposure zone, region of normal exposure and zone line.Above zone maybe be with a kind of existence the in five kinds of forms of Fig. 4 to Fig. 8 in pending image.

The exposure area that comparingunit 20 is used for each pixel of illumination layer image and 18 is divided relatively and select corresponding calibration curve.

Correctingunit 22 is used for proofreading and correct the new illumination layer pixel value of generation according to corresponding calibration curve.Illumination layer image after the correction and texture layer image produce compressed images throughfusion device 24.

Compressedimages output unit 26 is exported after being used for pixel value is mapped to suitable color space.

See also shown in Figure 3ly again, this realizes the method for image high dynamic range compression, comprising following steps:

(1) original image of input is analyzed, is calculated and divide the exposure area of pending image, may further comprise the steps:

(a) monochrome information of original image is analyzed, and is marked off existing region of normal exposure, under-exposure zone, overexposure zone and zone line, may further comprise the steps:

(i) original image is γ according to the calibration curve of following formula representative in brightness₁＞1 mapping, the map image y after obtaining proofreading and correct₁:

${\mathrm{<figure-callout\; label="y"\; filenames="HDA0000121126220000031.png,HDA0000121126220000032.png"\; state="\{\{state\}\}">y</figure-callout>}}_1=x^{1/{\mathrm{\&gamma;}}_1};$

And original image is γ according to the calibration curve of following formula representative in brightness₂＜1 mapping, the map image y after obtaining proofreading and correct₂:

$y_2=x^{1/{\mathrm{\&gamma;}}_2};$

Wherein, x is the original image of input; This γ₁Value is 22, γ₂Value is 0.4545;

(ii) calculate the original image x and the map image y of input respectively₁And y₂In the gradient information of each pixel;

(iii) successively with map image y₁Do difference with the corresponding gradient of each pixel of the original image x that imports and obtain amplitude of variation Δ y₁If x is this amplitude of variation Δ y₁X is greater than the first threshold th of systemic presupposition₁, then include this pixel in under-exposure zone; If this amplitude of variation Δ y₁X is less than the 3rd threshold value th of systemic presupposition₃, then include this pixel in region of normal exposure; Otherwise include this pixel in zone line;

(iv) successively with map image y₂Do difference with the corresponding gradient of each pixel of the original image x that imports and obtain amplitude of variation Δ y₂If x is this amplitude of variation Δ y₂X is greater than the second threshold value th of systemic presupposition₂, then include this pixel in the overexposure zone; If this amplitude of variation Δ y₂X is less than the 3rd threshold value th of systemic presupposition₃, then include this pixel in region of normal exposure; Otherwise include this pixel in zone line;

(b) calculate and obtain the luminance threshold in under-exposure zone, the luminance threshold in overexposure zone and the luminance threshold of region of normal exposure, may further comprise the steps:

(i) count the brightness average m of each pixel in under-exposure zone₁With variance v₁, and with m₁+ λ v₁As the luminance threshold in under-exposure zone, wherein λ is the adjustment factor;

(ii) count the brightness average m of each pixel in overexposure zone₂With variance v₂, and with m₂-λ v₂Luminance threshold as the overexposure zone;

(iii) count the brightness average m of each pixel of region of normal exposure₃With variance v₃, and with m₃+ λ v₃As the higher limit of the luminance threshold of region of normal exposure, with m₃-λ v₃Lower limit as the luminance threshold of region of normal exposure;

(2) each pixel and the described exposure area with pending image compares, and selects corresponding calibration curve, may further comprise the steps:

(a), then select the calibration curve of the brightness value of this pixel of lifting if described pixel is positioned at under-exposure zone; 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), then select the calibration curve of the brightness value of this pixel of inhibition if described pixel is positioned at the overexposure zone; 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), then select to keep the brightness value of this pixel constant or finely tune the calibration curve of this pixel brightness value if described pixel is positioned at region of normal exposure; The brightness value of this 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;

(d), then select preset zone line gamma correction curve if described pixel is positioned at zone line; 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,x₂Be the minimum pixel brightness value in the zone of the overexposure of zone line zone one side, y₂Be the corresponding map intensity values of this pixel value, x₁Be the maximum pixel brightness value in the zone of the under-exposure regional side of zone line, y₁Be the corresponding map intensity values of this pixel value;

(3), proofread and correct the new pixel value of generation according to corresponding calibration curve to each pixel;

(4) described new pixel value is mapped to suitable color space and 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, the B component, the mapping relations of pixel brightness value that this is new and original pixels brightness value are:

$R_{\mathrm{OUT}}=\frac{y}{x}\&times;R_{\mathrm{IN}};$

$G_{\mathrm{OUT}}=\frac{y}{x}\&times;G_{\mathrm{IN}};$

$B_{\mathrm{OUT}}=\frac{y}{x}\&times;B_{\mathrm{IN}};$

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 the 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 with the original image of described illumination layer image as input;

Described step (4) is further comprising the steps of afterwards:

(5) illumination layer image and the texture layer image exported the back be will handle and back generation compressed images and output merged.

In the middle of reality was used, the present invention realized through following technical scheme:

This quick high dynamic range compression method; Through input picture is analyzed; Divide normal exposure, under-exposure or overexposure and zone line; The brightness and the contrast of maintenance region of normal exposure in under-exposure or brightness that overexposure is regional and the contrast in adjustment are compressed the brightness and the contrast of zone line simultaneously.

Since piece image generally by region of normal exposure, under-exposure or overexposure is regional and zone line in a kind of or whole the composition.So-called region of normal exposure is meant can on LDR equipment, normally show or posting field, dark or bright excessively situation can not occur.And what is called is under-exposure or overexposure is regional, is meant to cross dark or bright excessively zone when demonstration is perhaps write down on LDR equipment.Zone line then is between the zone between the above two.In order to adjust under-exposure simultaneously in the contrast that guarantees region of normal exposure or overexposure is regional, improve compression effectiveness, we adopt the thinking of dividing based on the exposure area to carry out high dynamic range compression.

The thought of method of the present invention is summed up as follows:

At first the monochrome information of original image or illumination layer is analyzed, marked off the region of normal exposure that possibly exist, under-exposure or overexposure is regional and zone line.Region of normal exposure and under-exposure or overexposure be regional all distinguishes the one or more threshold values in corresponding the input picture valid pixel scope, and the zone between region of normal exposure threshold value and under-exposure or the regional threshold value of overexposure is called zone line.Possible threshold distribution such as Fig. 4 are to shown in Figure 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 zone (0～L1), zone line (L1～L2), region of normal exposure (L2～L3), zone line (L3～L4), overexposure zone (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 zone (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 zone (0～L1), zone line (L1～L2), region of normal exposure (L2～1).When region of normal exposure did not exist, like Fig. 7, shown in 8, entire image all was under-exposure zone or overexposure zone.

The method of analyzing and dividing various exposure areas has a lot, as passing through histogram analysis, through 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.

Completion begins each zone is shone upon after the exposure area of original image or illumination layer is divided.At first shine upon for region of normal exposure; For the mapping principle in this zone is to be prerequisite not lose overall contrast, maximum after therefore should the normalization of zone 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 that this is regional have a lot, can also can be 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 zone is shone upon; For the mapping principle in this zone is to be prerequisite with the brightness that promotes dark portion zone, so this zone 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 that this is regional have a lot, can through predefined correction curve also can through current pixel and on every side the 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 the overexposure zone is shone upon; For the mapping principle in this zone is to be prerequisite with the brightness that reduced bright area, so this zone 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 that this is regional have a lot, can through predefined correction curve also can through current pixel and on every side the 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.

At last middle zone is shone upon; For the mapping principle in this zone is to be prerequisite to reduce this regional overall contrast, so there is inhibition by a relatively large margin in maximum and the missionary society of minimum value of difference after with respect to the normalization of input pixel that this zone is mapped to maximum and minimum value after the normalization of output pixel.The computational methods of the mapping curve that this is regional have a lot, the under-exposure zone after can also can passing through to shine upon through predefined correction curve or the input of overexposure zone and region of normal exposure and output pixel dynamic calculation 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.

So far, high dynamic range compression method of the present invention finishes, if be applied to the illumination layer compression in the partial compression method, then combines the final compression result of back output with texture layer through the illumination layer after this method compression; If be applied to overall compression method, then compaction algorithms finishes.

Flow chart as an execution mode of high dynamic range compression method of the present invention specifically comprises the steps:

(1) calculates and obtains the under-exposure regional luminance threshold value that possibly exist, overexposure zone luminance threshold and the region of normal exposure luminance threshold that is applied to present image.

(2) from original image, obtain a pending pixel, as current pixel.

(3) brightness of calculating current pixel.It should be noted that; Dividing and shine upon based on the exposure area of brightness is a specific embodiment of this patent; No matter how to divide in concrete the realization and shine upon for exposure area and corresponding threshold; 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; Likewise, 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 that counts are compared,, then promote this pixel brightness value if current pixel is positioned at under-exposure zone.This pixel intensity output valve can through predefined correction curve also can through current pixel and on every side the adjacent pixel values dynamic calculation obtain etc.Adopt y=x in the present embodiment^{1/ γ}Correction curve calculate brightness after the rectification in under-exposure zone, γ=2.2, x is for correcting the preceding pixel brightness value, y is for correcting the back pixel brightness value.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 the overexposure zone, then suppress this pixel brightness value.This pixel intensity output valve can through predefined correction curve also can through current pixel and on every side the adjacent pixel values dynamic calculation obtain etc.Adopt y=x in the present embodiment^{1/ γ}Correction curve calculate brightness after the rectification in overexposure zone, γ=0.4545, x is for correcting the preceding pixel brightness value, y is for correcting the back pixel brightness value.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, then remains unchanged or finely tune this pixel brightness value.The computational methods of this pixel intensity output valve have a lot, can also can be S curve etc. for slope is fixed as a curve of 1.Brightness after the rectification of the correction curve calculating region of normal exposure of employing y=x in the present embodiment, x is for correcting the preceding pixel brightness value, and y is a pixel brightness value after the rectification.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; Brightness after the rectification of the correction curve calculating zone line of employing y=kx+b in the present embodiment; X is for correcting the preceding pixel brightness value; Y is for correcting back pixel brightness value,

X wherein₂Be the minimum pixel brightness value of zone line right side area, y₂Be the corresponding map intensity values of this pixel value, x₁Be the maximum pixel brightness value of zone line left field, y₁Be the corresponding map intensity values of 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) according to the relation of output pixel brightness value, the brightness value of output pixel is mapped to R, G, B component with the input pixel brightness value.Mapping relations in the present embodiment do$R_{\mathrm{OUT}}=\frac{y}{x}\&times;R_{\mathrm{IN}},$$G_{\mathrm{OUT}}=\frac{y}{x}\&times;G_{\mathrm{IN}},$$B_{\mathrm{OUT}}=\frac{y}{x}\&times;B_{\mathrm{IN}}.$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.The brightness value of pixel is mapped to R, G, B component has a lot of methods, except above cited method, no matter finally adopts which kind of method in concrete the realization, does not all deviate from basic thought of the present invention and does not exceed protection scope of the present invention.

Said step (1) comprises following steps:

(11) entire image is the y=x of γ=2.2 and γ=0.4545 respectively in brightness^{1/ γ}Mapping, output is respectively y₁And y₂

(12) difference calculating input image x and mapping y₁And y₂The 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 with y₁The gradient corresponding with each pixel of input picture x is poor Δ y₁X, when its amplitude of variation greater than threshold value th₁The time, this pixel included in owe the zone of exposing to the sun.Count and owe to expose to the sun mean value of areas m₁With variance v₁, calculate m₁+ λ v₁As under-exposure regional luminance threshold value, wherein λ is the adjustment factor.

Similarly, successively with y₂The gradient corresponding with each pixel of input picture x is poor Δ y₂X, when its amplitude of variation greater than threshold value th₂The time, include this pixel in the overexposure zone.Count overexposure mean value of areas m₂With variance v₂, calculate m₂-λ v₂As overexposure zone luminance threshold.As Δ y₁X and Δ y₂The amplitude of variation of x is less than threshold value th₃The time, include this pixel in region of normal exposure.Count the average m of region of normal exposure₃With variance v₃, calculate m₃+ λ v₃, m₃-λ v₃Bound as the region of normal exposure luminance threshold.The transition in region of normal exposure and under-exposure zone and region of normal exposure and overexposure zone is called zone line.

The system and the method thereof of above-mentioned realization image high dynamic range compression have been adopted, owing to, divide normal exposure and under-exposure zone wherein through input picture is analyzed; Promote under-exposure regional luminance, keep region of normal exposure brightness, thus efficiently solve damage region of normal exposure in the high dynamic range compression method, halation (Halo) and the excessive problem of picture contrast loss appear in the border; And when keeping the region of normal exposure contrast; Promote the observability in under-exposure zone and overexposure zone, not only can directly apply to overall high Dynamic Compression, and can apply to brightness (illumination layer) compression in the local high Dynamic Compression; Simultaneously; Computational complexity of the present invention is extremely low, is convenient to real-time processing, the processing procedure quickness and high efficiency; Stable and reliable working performance, the scope of application are comparatively extensive.

In this specification, the present invention is described with reference to its certain embodiments.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 (18)

1. a system that realizes the image high dynamic range compression is characterized in that, described system comprises:

The original image input unit is used to obtain pending image;

The exposure area computing unit is connected with described original image input unit, is used to calculate and divide the exposure area of pending image;

Comparing unit is connected with the exposure area computing unit with described original image input unit respectively, and the exposure area that is used for each pixel and this exposure area computing unit of pending image are divided relatively and select corresponding calibration curve;

Correcting unit is connected with described comparing unit, is used for proofreading and correct the new pixel value of generation according to corresponding calibration curve; And the compressed images output unit, be connected with described correcting unit, export after being used for pixel value is mapped to suitable color space.

2. the system of realization image high dynamic range compression according to claim 1 is characterized in that, described exposure area is through the pixel value of analyzing pending image and the zone of pending image being cut apart according to the difference of depth of exposure.

3. the system of realization image high dynamic range compression according to claim 2 is characterized in that, described exposure area comprises overexposure zone, under-exposure zone, region of normal exposure and zone line.

4. the system of realization image high dynamic range compression according to claim 1 is characterized in that, also comprises in the described system:

Illumination/details separator is connected with described original image input unit, is used for isolating illumination layer image and texture layer image from original image, and described illumination layer image is delivered in the computing unit of described exposure area;

Fusion device; Receive the texture layer image that illumination layer image and illumination/details separator after the correction of described correcting unit output are exported; And the illumination layer image after will proofreading and correct and texture layer image merge the back and produce compressed images, and export described compressed images output unit to.

5. a method that realizes the image high dynamic range compression is characterized in that, described method may further comprise the steps:

(1) original image of input is analyzed, calculated and divide the exposure area of pending image;

(2) each pixel and the described exposure area with pending image compares, and selects corresponding calibration curve;

(3), proofread and correct the new pixel value of generation according to corresponding calibration curve to each pixel;

(4) described new pixel value is mapped to suitable color space and output.

6. the method for realization image high dynamic range compression according to claim 5 is characterized in that, the exposure area of dividing pending image is analyzed and calculated to described original image to input, may further comprise the steps:

(11) monochrome information of original image is analyzed, and marked off existing region of normal exposure, under-exposure zone, overexposure zone and zone line;

(12) calculate and obtain the luminance threshold in under-exposure zone, the luminance threshold in overexposure zone and the luminance threshold of region of normal exposure.

7. the method for realization image high dynamic range compression according to claim 6; It is characterized in that; Existing region of normal exposure, under-exposure zone, overexposure zone and zone line are analyzed and marked off to described monochrome information to original image, may further comprise the steps:

(111) original image is γ according to the calibration curve of following formula representative in brightness₁＞1 mapping, the map image y after obtaining proofreading and correct₁:

$y_1=x^{1/{\mathrm{\&gamma;}}_1};$

And original image is γ according to the calibration curve of following formula representative in brightness₂＜1 mapping, the map image y after obtaining proofreading and correct₂:

$y_2=x^{1/{\mathrm{\&gamma;}}_2};$

Wherein, x is the original image of input;

(112) calculate original image x and the map image y that imports respectively₁And y₂In the gradient information of each pixel;

(113) successively with map image y₁Do difference with the corresponding gradient of each pixel of the original image x that imports and obtain amplitude of variation Δ y₁If x is this amplitude of variation Δ y₁X is greater than the first threshold th of systemic presupposition₁, then include this pixel in under-exposure zone; If this amplitude of variation Δ y₁X is less than the 3rd threshold value th of systemic presupposition₃, then include this pixel in region of normal exposure; Otherwise include this pixel in zone line;

(114) successively with map image y₂Do difference with the corresponding gradient of each pixel of the original image x that imports and obtain amplitude of variation Δ y₂If x is this amplitude of variation Δ y₂X is greater than the second threshold value th of systemic presupposition₂, then include this pixel in the overexposure zone; If this amplitude of variation Δ y₂X is less than the 3rd threshold value th of systemic presupposition₃, then include this pixel in region of normal exposure; Otherwise include this pixel in zone line.

8. the method for realization image high dynamic range compression according to claim 7 is characterized in that, described γ₁Value is 2.2.

9. the method for realization image high dynamic range compression according to claim 7 is characterized in that, described γ₂Value is 0.4545.

10. the method for realization image high dynamic range compression according to claim 7; It is characterized in that; Described calculating is also obtained the luminance threshold in under-exposure zone, the luminance threshold in overexposure zone and the luminance threshold of region of normal exposure, may further comprise the steps:

(121) count the brightness average m of each pixel in under-exposure zone₁With variance v₁, and with m₁+ λ v₁As the luminance threshold in under-exposure zone, wherein λ is the adjustment factor;

(122) count the brightness average m of each pixel in overexposure zone₂With variance v₂, and with m₂-λ v₂Luminance threshold as the overexposure zone;

(123) count the brightness average m of each pixel of region of normal exposure₃With variance v₃, and with m₃+ λ v₃As the higher limit of the luminance threshold of region of normal exposure, with m₃-λ v₃Lower limit as the luminance threshold of region of normal exposure.

11. the method for realization image high dynamic range compression according to claim 6 is characterized in that, described each pixel and described exposure area with pending image compares and selects corresponding calibration curve, may further comprise the steps:

(21), then select the calibration curve of the brightness value of this pixel of lifting if described pixel is positioned at under-exposure zone;

(22), then select the calibration curve of the brightness value of this pixel of inhibition if described pixel is positioned at the overexposure zone;

(23), then select to keep the brightness value of this pixel constant or finely tune the calibration curve of this pixel brightness value if described pixel is positioned at region of normal exposure;

(24), then select preset zone line gamma correction curve if described pixel is positioned at zone line.

12. the method for realization image high dynamic range compression according to claim 11 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.

13. the method for realization image high dynamic range compression according to claim 11 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.

14. the method for realization image high dynamic range compression according to claim 11 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.

15. the method for realization image high dynamic range compression according to claim 11 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,x₂Be the minimum pixel brightness value in the zone of the overexposure of zone line zone one side, y₂Be the corresponding map intensity values of this pixel value, x₁Be the maximum pixel brightness value in the zone of the under-exposure regional side of zone line, y₁Be the corresponding map intensity values of this pixel value.

16. the method for realization image high dynamic range compression according to claim 11 is characterized in that, described with new pixel value be mapped to suitable color space and output, be 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, the B component.

17. the method for realization image high dynamic range compression according to claim 16 is characterized in that, the described new pixel brightness value and the mapping relations of original pixels brightness value are:

$R_{\mathrm{OUT}}=\frac{y}{x}\&times;R_{\mathrm{IN}};$

$G_{\mathrm{OUT}}=\frac{y}{x}\&times;G_{\mathrm{IN}};$

$B_{\mathrm{OUT}}=\frac{y}{x}\&times;B_{\mathrm{IN}};$

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.

18. the method according to each described realization image high dynamic range compression in the claim 5 to 17 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 with the original image of described illumination layer image as input;

Described step (4) is further comprising the steps of afterwards:

(5) illumination layer image and the texture layer image exported the back be will handle and back generation compressed images and output merged.

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