CN103973941A - Method and system for adjusting dynamic contrast of digital image or video - Google Patents

Abstract

The invention discloses a method for adjusting the dynamic contrast of a digital image or video. The method comprises the following steps that a frame of image in the digital image or video is read; a pixel brightness value probability cumulative distribution function cdf() of the image is calculated; when the image is a gray level image, the contrast of the current gray level image is adjusted with a relational expression (please see the specific formula in the specification); when the image is a color image, the contrast of the current color image is adjusted with a relational expression (please see the specific formula in the specification), wherein zi=f(Ei), zi is the output pixel value of a pixel point at exposure brightness Ei, f() is a mapping function, Yi is a brightness value, and Ci is one channel in RGB three color channels. The invention further discloses a system for adjusting the dynamic contrast of the digital image or video.

Description

Dynamic contrast method of adjustment and the system of digital image

Technical field

The present invention relates to digital image field, particularly relate to a kind of dynamic contrast method of adjustment and system of digital image.

Background technology

Contrast refers to the measurement of the different brightness levels between white the brightest in image and the darkest black, and the larger contrast of disparity range is larger.Because the dynamic range of actual scene is usually more than 100dB, and the sensor element that traditional digital cameras adopts (CCD or CMOS) generally can only have the dynamic range of about 60dB, this just makes the photometric system of camera be subject to the impact in highlighted or low clear zone, compress the quantification ash exponent number in other regions, cause overall contrast to decline, loss in detail.

The enhancing of existing picture contrast can utilize Gamma (gamma) parameter of display to adjust, and adjusts picture contrast by the relation that changes grey scale signal and brightness.But single contrast settings also cannot be applicable to all images.For instance, for an image that overall brightness is higher, user may select the Gamma parameter that brightness is large or the setting of change contrast strengthens picture contrast, but such setting is during for the lower image of brightness, can make the part of image low-light level too dark, make image quality variation and lose details.

Summary of the invention

The technical problem that the present invention solves is to provide a kind of dynamic contrast method of adjustment and system of digital image, can, effectively according to the histogram distribution of current scene, control adaptively, strengthens contrast.

For solving the problems of the technologies described above, the invention provides a kind of dynamic contrast method of adjustment of digital image, it comprises the steps:

Read the two field picture in piece image or video;

Calculate the probability cumulative distribution function cdf () of the pixel brightness value of described image;

In the time that being gray scale image, image adopts relational expression: contrast to current gray scale image is adjusted; In the time that image is coloured image, adopt relational expression: contrast to current coloured image is adjusted, wherein, and z _i=f (E _i), z _ifor pixel is at exposure brightness E _ioutput pixel value, f () is mapping function, Y _ibrightness value, C _iit is a passage in tri-color channels of RGB.

Wherein, the pixel brightness value probability cumulative distribution function cdf () of the described image of described calculating comprises:

Calculate the brightness histogram of described image, obtain probability density function pdf (), adopt following relational expression to calculate probability density function pdf () is done to index normalization:

${\mathrm{pdf}\left(Z_i\right)}^{\′}={\left(\frac{\mathrm{pdf}\left(Z_i\right)-\min \left\{\mathrm{pdf}(\·)\right\}}{\max \left\{\mathrm{pdf}(\·)\right\}-\min \left\{\mathrm{pdf}(\·)\right\}}\right)}^a,$ A is exponential factor;

Adopt following relational expression that probability density function pdf () normalization is distributed:

${\mathrm{pdf}\left(Z_i\right)}^{\′\′}=\frac{{\mathrm{pdf}\left(Z_i\right)}^{\′}}{{{\mathrm{\Σ}}_i\mathrm{pdf}\left(Z_i\right)}^{\′}},$

Adopt following relational expression calculating probability cumulative distribution function:

$\mathrm{cdf}\left(Z_i\right)={\mathrm{\Σ}}_{j=0}^i\mathrm{pdf}{\left(Z_i\right)}^{\′\′}.$

Wherein, further comprise step:

Regulate exponential factor a to control the intensity that contrast promotes.

Wherein, further comprise step: image is kept away to dodge and process.

Wherein, described to image keep away dodge process comprise:

Adopt to cdf () amplitude limit, if z _i-cdf (Z _i) > T (z _i), z _i-cdf (Z _i)=T (Z _i); If z _i-cdf (Z _i) <-T (z _i), z _i-cdf (Z _it (the Z of)=- _i), wherein T (Z _i) be and z _irelevant threshold function table.

Wherein, described to image keep away dodge process comprise:

Adopt the level and smooth mode of interframe, adopt following relational expression: image is kept away to dodge and process, wherein α is interframe smoothing factor, f (Z _i) be GTG mapping function.

For solving the problems of the technologies described above, the invention provides a kind of dynamic contrast adjustment System of digital image, described system comprises:

One reading unit, for reading a two field picture of piece image or video;

One probability cumulative distribution computing unit, for calculating the pixel brightness value probability cumulative distribution function cdf () of described image;

One contrast adjustment unit, in the time that image is gray scale image, described contrast adjustment unit adopts relational expression: contrast to current gray scale image is adjusted; In the time that image is coloured image, described contrast adjustment unit adopts relational expression: contrast to current coloured image is adjusted, wherein, and z _i=f (E _i), z _ifor pixel is at exposure brightness E _ioutput pixel value, f () is linear function, Y _ibrightness value, C _iit is a passage in tri-color channels of RGB.

Wherein, described system further comprises a probability density calculation unit and a normalization unit, described probability density computing unit is for calculating the brightness histogram of described image, obtain probability density function pdf (), described normalization unit adopts following relational expression to calculate probability density function pdf () is done to index normalization:

${\mathrm{pdf}\left(Z_i\right)}^{\&prime;}={\left(\frac{\mathrm{pdf}\left(Z_i\right)-\min \left\{\mathrm{pdf}(\&CenterDot;)\right\}}{\max \left\{\mathrm{pdf}(\&CenterDot;)\right\}-\min \left\{\mathrm{pdf}(\&CenterDot;)\right\}}\right)}^a,$ A is exponential factor;

Described normalization unit adopts following relational expression that probability density function pdf () normalization is distributed:

${\mathrm{pdf}\left(Z_i\right)}^{\&prime;\&prime;}=\frac{{\mathrm{pdf}\left(Z_i\right)}^{\&prime;}}{{{\mathrm{\&Sigma;}}_i\mathrm{pdf}\left(Z_i\right)}^{\&prime;}},$

Described probability cumulative distribution computing unit adopts following relational expression calculating probability cumulative distribution function:

$\mathrm{cdf}\left(Z_i\right)={\mathrm{\&Sigma;}}_{j=0}^i\mathrm{pdf}{\left(Z_i\right)}^{\&prime;\&prime;}.$

Wherein, described system further comprises a parameter regulon, for regulating exponential factor a to control the intensity that contrast promotes.

Wherein, described system further comprises keeps away sudden strain of a muscle processing unit, described in keep away and dodge processing unit for avoiding video playback, adjust in real time the problem of the film flicker bringing.

Wherein, described in keep away dodge processing unit to cdf () amplitude limit to image keep away dodge process, work as z _i-cdf (Z _i) > T (z _i) time, z _i-cdf (Z _i)=T (Z _i); Work as z _i-cdf (Z _i) <-T (z _i) time, z _i-cdf (Z _it (the Z of)=- _i), wherein T (Z _i) be and z _irelevant threshold function table.

Wherein, described in keep away and dodge processing unit and adopt interframe level and smooth mode, adopt following relational expression: image is kept away to dodge and process, wherein α is interframe smoothing factor, f (Z _i) be GTG mapping function.

With respect to prior art, by dynamic contrast method of adjustment and the system of above-mentioned digital image, can effectively strengthen the dynamic contrast of digital image.

Brief description of the drawings

Fig. 1 is the dynamic contrast method of adjustment schematic flow sheet of the digital image of the embodiment of the present invention;

Fig. 2 is the relatively schematic diagram of effect of the front and back of the dynamic contrast method of adjustment of the digital image of the embodiment of the present invention;

Fig. 3 is the module diagram of the dynamic contrast adjustment System of the digital image of the embodiment of the present invention.

Embodiment

Refer to Fig. 1, the schematic flow sheet of the dynamic contrast method of adjustment of the digital image that the embodiment of the present invention provides.As shown in Figure 1, the dynamic contrast method of adjustment of described digital image comprises the steps:

S101: read a certain frame in piece image or video, be designated as I.

S102: calculate the brightness histogram of I, obtain probability density function pdf ().

Described calculating brightness histogram, is also the number of times that probability density function pdf () refers to the pixel appearance of calculating corresponding grey scale level in I, forms the distribution of pixel value in whole luminance dynamic range in I.Wherein histogram can be designated as a vectorial H=[p ₁, p ₂..., p _n].This vector meets:

p _i＝#{(x，y)|I(x，y)＝x _i}；

Wherein x _irepresent any gray scale.#{ (x, y) | I _{(x, y)}=x _irepresent that brightness value in I equals the number of element in set that the pixel of xi forms.I _{(x, y)}represent to be positioned at coordinate (x, y) and to locate the brightness value of pixel.This set is designated as to X _i=(x, y) | I _{(x, y)}=x _i.Described luminance dynamic range refers to the scope of all possible brightness value appearance of being determined by the number of bits of pixel value in I.If pixel value is a k bit number, dynamic range is 0 to 2 ^k-1.In the present embodiment, consider 8 bit image, dynamic range 0 to 255.

For gray-scale map, only need be to the luminance channel compute histograms H of I.For cromogram, need respectively tri-path computations of RGB to be gone out to three histogram Hc, c=R, G, B.

The index normalization of S103: calculating probability density function pdf (), and probability density function pdf () normalization is distributed.

In the present embodiment, adopt the index normalization of following relational expression calculating probability density function pdf ():

${\mathrm{pdf}\left(Z_i\right)}^{\&prime;}={\left(\frac{\mathrm{pdf}\left(Z_i\right)-\min \left\{\mathrm{pdf}(\&CenterDot;)\right\}}{\max \left\{\mathrm{pdf}(\&CenterDot;)\right\}-\min \left\{\mathrm{pdf}(\&CenterDot;)\right\}}\right)}^a,$ A is exponential factor, and it can arrange according to demand and arbitrarily.

In the present embodiment, adopt following relational expression that probability density function pdf () normalization is distributed:

${\mathrm{pdf}\left(Z_i\right)}^{\&prime;\&prime;}=\frac{{\mathrm{pdf}\left(Z_i\right)}^{\&prime;}}{{{\mathrm{\&Sigma;}}_i\mathrm{pdf}\left(Z_i\right)}^{\&prime;}}.$

S104: calculating probability cumulative distribution function cdf ().

In the present embodiment, adopt following relational expression calculating probability cumulative distribution function:

$\mathrm{cdf}\left(Z_i\right)={\mathrm{\&Sigma;}}_{j=0}^i\mathrm{pdf}{\left(Z_i\right)}^{\&prime;\&prime;}.$

Cdf () is probability cumulative distribution function, i.e. Probability (Z < z _i); z _i=f (E _i), z _ifor pixel is at exposure brightness E _ioutput pixel value.

Be understandable that, also can omit by step S103, and direct calculating probability cumulative distribution function cdf () be not limited to the present embodiment.

S105: adopt following GTG mapping function in the time that image is gray scale image contrast to current gray scale image is adjusted; In the time that image is coloured image, adopt with minor function contrast to current coloured image is adjusted.

Wherein, f () is mapping function, and Yi is brightness value, C _iit is a passage in tri-color channels of RGB.Because sample space is image itself, GTG mapping function itself be adaptive.Can see, in the time of zi=1, and work as z _i=0 o'clock, so described GTG mapping function itself be bounded and normalized.In the present embodiment, z _iall normalize to 0～1, consider 8 bit image, 0≤i≤255, take advantage of factor quantification to 8bit with one 255.

In S105, travel through whole digital image, i.e. each pixel of image I.In the time that image is RGB coloured image, asks for brightness value Y, then adopt relational expression calculate new color pixel values.In the time that image is GTG figure, adopt relational expression calculate GTG mapping value as new pixel value.

In the present embodiment, further comprise following two steps:

S106: regulate parameter, control the intensity that contrast promotes.

Without loss of generality, in the present embodiment, by probability density function pdf () is done to index normalization, thereby function cdf () is revised, accomplish that better parameter regulates.

By relational expression: $\mathrm{cdf}\left(Z_i\right)={\mathrm{\&Sigma;}}_{j=0}^i\mathrm{pdf}{\left(Z_i\right)}^{\&prime;\&prime;}.$ Relational expression: ${\mathrm{pdf}\left(Z_i\right)}^{\&prime;\&prime;}=\frac{{\mathrm{pdf}\left(Z_i\right)}^{\&prime;}}{{{\mathrm{\&Sigma;}}_i\mathrm{pdf}\left(Z_i\right)}^{\&prime;}},$ And relational expression: ${\mathrm{pdf}\left(Z_i\right)}^{\&prime;}={\left(\frac{\mathrm{pdf}\left(Z_i\right)-\min \left\{\mathrm{pdf}(\&CenterDot;)\right\}}{\max \left\{\mathrm{pdf}(\&CenterDot;)\right\}-\min \left\{\mathrm{pdf}(\&CenterDot;)\right\}}\right)}^a,$ Can see, a more cdf is more tending towards linear, therefore can regulate exponential factor a to control the intensity that contrast promotes.

S107: image is kept away to dodge and process.

Consider video playback, should avoid adjusting in real time the film flicker bringing.The present embodiment adopts the problem of the method for cdf () amplitude limit being avoided adjusting in real time the film flicker bringing.If i.e. z _i-cdf (Z _i) > T (z _i), z _i-cdf (Z _i)=T (Z _i); If z _i-cdf (Z _i) <-T (z _i), z _i-cdf (Z _it (the Z of)=- _i), wherein T (Z _i) be and z _irelevant threshold function table, a kind of special case is T (Z _i)=T ₀.

Be understandable that, also can adopt the level and smooth mode of interframe to reach and avoid the real-time problem of adjusting the film flicker bringing.As adopt following relational expression: image is kept away to dodge and process, wherein α is interframe smoothing factor, f (Z _i) be GTG mapping function.

In other embodiments, if computational resource is less, step S103 can omit; If computational resource is enough, the present embodiment adopts step S103 to control the intensity that contrast promotes.If only single frames picture is carried out to contrast lifting, step S106 is not necessary, if video is carried out to contrast lifting, step S107 can effectively avoid film flicker.Be not limited to the present embodiment.

By Fig. 2, effect contrast figure before and after dynamic contrast regulates, can find out, by the dynamic contrast method of adjustment of above-mentioned digital image, can effectively strengthen the dynamic contrast of digital image.

Refer to Fig. 3, Fig. 3 is the structural representation of the adjustment System of the dynamic contrast of the digital image of the embodiment of the present invention.As shown in Figure 3, described adjustment System 20 comprises: a reading unit 21, probability density computing unit 22, normalization unit 23, probability cumulative distribution computing unit 24 and a contrast adjustment unit 25.

In embodiments of the present invention, described reading unit 21, for reading a certain frame of piece image or video, is designated as I.Described probability density computing unit 22 is connected with described reading unit 21, and described probability density computing unit 22, for calculating the brightness histogram of I, obtains probability density function pdf ().Described normalization unit 23 is connected with described probability density computing unit 22, and described normalization unit 23 is for the index normalization of calculating probability density function pdf (), and probability density function pdf () normalization is distributed.Described probability cumulative distribution computing unit 24 is connected with described normalization unit 23, and described probability cumulative distribution computing unit 24 is for calculating probability cumulative distribution function cdf ().Described contrast adjustment unit 25 is connected with described probability cumulative distribution function computing unit 24, described contrast adjustment unit 25 is adjusted for the contrast to image, also,, in the time that image is gray scale image, described contrast adjustment unit 25 adopts following GTG mapping function contrast to current gray scale image is adjusted; In the time that image is coloured image, described contrast adjustment unit 25 adopts following relational expression contrast to current coloured image is adjusted.

In embodiments of the present invention, described calculating brightness histogram, is also the number of times that probability density function pdf () refers to the pixel appearance of calculating corresponding grey scale level in I, forms the distribution of pixel value in whole luminance dynamic range in I.Wherein histogram can be designated as a vectorial H=[p ₁, p ₂..., p _n].This vector meets:

p _i＝#{(x，y)|I _(x，y)＝x _i}；

Wherein x _irepresent any gray scale.#{ (x, y) | I _{(x, y)}=x _irepresent that brightness value in I equals the number of element in set that the pixel of xi forms.I _{(x, y)}represent to be positioned at coordinate (x, y) and to locate the brightness value of pixel.This set is designated as to X _i=(x, y) | I _{(x, y)}=x _i.Described luminance dynamic range refers to the scope of all possible brightness value appearance of being determined by the number of bits of pixel value in I.If pixel value is a k bit number, dynamic range is 0 to 2 ^k-1.In the present embodiment, consider 8 bit image, dynamic range 0 to 255.

For gray-scale map, only need be to the luminance channel compute histograms H of I.For cromogram, need respectively tri-path computations of RGB to be gone out to three histogram Hc, c=R, G, B.

In the present embodiment, described normalization unit 23 adopts following relational expression to adopt the index normalization to calculating probability density function pdf ():

${\mathrm{pdf}\left(Z_i\right)}^{\&prime;}={\left(\frac{\mathrm{pdf}\left(Z_i\right)-\min \left\{\mathrm{pdf}(\&CenterDot;)\right\}}{\max \left\{\mathrm{pdf}(\&CenterDot;)\right\}-\min \left\{\mathrm{pdf}(\&CenterDot;)\right\}}\right)}^a,$ A is exponential factor, and it can arrange according to demand and arbitrarily.

In the present embodiment, described normalization unit 23 adopts following relational expression that probability density function pdf () normalization is distributed:

${\mathrm{pdf}\left(Z_i\right)}^{\&prime;\&prime;}=\frac{{\mathrm{pdf}\left(Z_i\right)}^{\&prime;}}{{{\mathrm{\&Sigma;}}_i\mathrm{pdf}\left(Z_i\right)}^{\&prime;}}.$

In the present embodiment, described probability cumulative distribution computing unit 24 adopts following relational expression calculating probability cumulative distribution function:

$\mathrm{cdf}\left(Z_i\right)={\mathrm{\&Sigma;}}_{j=0}^i\mathrm{pdf}{\left(Z_i\right)}^{\&prime;\&prime;}.$

Cdf () is probability function, i.e. Probability (Z < z _i); z _i=f (E _i), z _ifor pixel is at exposure brightness E _ioutput pixel value.

In the present embodiment, in the time that image is gray scale image, described contrast adjustment unit 25 adopts following GTG mapping function contrast to current gray scale image is adjusted; In the time that image is coloured image, described contrast adjustment unit 25 adopts following function f (C _i)= contrast to current coloured image is adjusted.

Wherein, f () is mapping function, Y _ibrightness value, C _iit is a passage in tri-color channels of RGB.Because sample space is image itself, GTG mapping function itself be adaptive.Can see, work as z _i=1 o'clock, and work as z _i=0 o'clock, so described GTG mapping function itself be bounded and normalized.

In the present embodiment, z _iall normalize to 0～1, consider 8 bit image, 0≤i≤255, take advantage of factor quantification to 8bit with one 255.

In the present embodiment, the intensity promoting in order to control contrast, the adjustment System 20 of described dynamic contrast further comprises a parameter regulon 26.

Described parameter regulon 26 and described contrast adjustment unit 25.The adjustment System 20 of described dynamic contrast is by probability density function pdf () is done to index normalization, thereby function cdf () is revised, and accomplishes that better parameter regulates.

By relational expression: $\mathrm{cdf}\left(Z_i\right)={\mathrm{\&Sigma;}}_{j=0}^i\mathrm{pdf}{\left(Z_i\right)}^{\&prime;\&prime;}.$ Relational expression: ${\mathrm{pdf}\left(Z_i\right)}^{\&prime;\&prime;}=\frac{{\mathrm{pdf}\left(Z_i\right)}^{\&prime;}}{{{\mathrm{\&Sigma;}}_i\mathrm{pdf}\left(Z_i\right)}^{\&prime;}},$ And relational expression: ${\mathrm{pdf}\left(Z_i\right)}^{\&prime;}={\left(\frac{\mathrm{pdf}\left(Z_i\right)-\min \left\{\mathrm{pdf}(\&CenterDot;)\right\}}{\max \left\{\mathrm{pdf}(\&CenterDot;)\right\}-\min \left\{\mathrm{pdf}(\&CenterDot;)\right\}}\right)}^a,$ Can see, a more cdf is more tending towards linear, and therefore described parameter regulon 26 is by regulating exponential factor a to control the intensity that contrast promotes.

In the present embodiment, for fear of video playback, adjust in real time the problem of the film flicker bringing, the adjustment System 20 of described dynamic contrast further comprises keeping away dodges processing unit 27.Described keep away dodge processing unit 27 also with described contrast adjustment unit 25.The described sudden strain of a muscle processing unit 27 of keeping away adopts the problem of the method for cdf () amplitude limit being avoided adjusting in real time the film flicker bringing.If i.e. z _i-cdf (z _i) > T (z _i), z _i-cdf (z _i)=T (z _i); If z _i-cdf (z _i) <-T (z _i), z _i-cdf (z _it (the z of)=- _i), wherein T (z _i) be and z _irelevant threshold function table, a kind of special case is T (z _i)=T ₀.

Be understandable that, described in keep away and dodge processing unit 27 and also can adopt the level and smooth mode of interframe to reach to avoid the problem of adjusting in real time the film flicker bringing.As adopt following relational expression: α z _i+ (1-α) f (Z _i), image is kept away to dodge and process, wherein α is interframe smoothing factor, f (Z _i) be GTG mapping function.

In other embodiments, described rate density calculation unit 22 and described normalization unit 23 can omit, and described reading unit 21 is directly connected with described probability cumulative distribution computing unit 24, described probability cumulative distribution computing unit 24 directly obtains probability cumulative distribution function, is not limited to the present embodiment.

In several embodiment provided by the present invention, should be understood that, disclosed system, apparatus and method, can realize by another way.For example, device embodiment described above is only schematic, for example, the division of described module or unit, be only that a kind of logic function is divided, when actual realization, can have other dividing mode, for example multiple unit or assembly can in conjunction with or can be integrated into another system, or some features can ignore, or do not carry out.Another point, shown or discussed coupling each other or direct-coupling or communication connection can be by some interfaces, indirect coupling or the communication connection of device or unit can be electrically, machinery or other form.

The described unit as separating component explanation can or can not be also physically to separate, and the parts that show as unit can be or can not be also physical locations, can be positioned at a place, or also can be distributed in multiple network element.Can select according to the actual needs some or all of unit wherein to realize the object of the present embodiment scheme.

In addition, the each functional unit in each embodiment of the present invention can be integrated in a processing unit, can be also that the independent physics of unit exists, and also can be integrated in a unit two or more unit.Above-mentioned integrated unit both can adopt the form of hardware to realize, and also can adopt the form of SFU software functional unit to realize.

If described integrated unit is realized and during as production marketing independently or use, can be stored in a computer read/write memory medium using the form of SFU software functional unit.Based on such understanding, the all or part of of the part that technical scheme of the present invention contributes to prior art in essence in other words or this technical scheme can embody with the form of software product, this computer software product is stored in a storage medium, comprise that some instructions (can be personal computers in order to make a computer equipment, server, or the network equipment etc.) or processor (processor) carry out all or part of step of method described in each embodiment of the present invention.And aforesaid storage medium comprises: USB flash disk, portable hard drive, read-only memory (ROM, Read-Only Memory), the various media that can be program code stored such as random access memory (RAM, Random Access Memory), magnetic disc or CD.

The foregoing is only embodiments of the invention; not thereby limit the scope of the claims of the present invention; every equivalent structure or conversion of equivalent flow process that utilizes specification of the present invention and accompanying drawing content to do; or be directly or indirectly used in other relevant technical fields, be all in like manner included in scope of patent protection of the present invention.

Claims (12)

1. a dynamic contrast method of adjustment for digital image, it comprises the steps:

Read the two field picture in piece image or video;

Calculate the pixel brightness value probability cumulative distribution function cdf () of described image;

In the time that being gray scale image, image adopts relational expression: contrast to current gray scale image is adjusted; In the time that image is coloured image, adopt relational expression: contrast to current coloured image is adjusted, wherein, and z _i=f (E _i), z _ifor pixel is at exposure brightness E _ioutput pixel value, f () is mapping function, Y _ibrightness value, C _iit is a passage in tri-color channels of RGB.

2. method according to claim 1, is characterized in that, the pixel brightness value probability cumulative distribution function cdf () of the described image of described calculating comprises:

Calculate the brightness histogram of described image, obtain probability density function pdf (), adopt following relational expression to calculate probability density function pdf () is done to index normalization:

${\mathrm{pdf}\left(Z_i\right)}^{\&prime;}={\left(\frac{\mathrm{pdf}\left(Z_i\right)-\min \left\{\mathrm{pdf}(\&CenterDot;)\right\}}{\max \left\{\mathrm{pdf}(\&CenterDot;)\right\}-\min \left\{\mathrm{pdf}(\&CenterDot;)\right\}}\right)}^a,$ A is exponential factor;

Adopt following relational expression that probability density function pdf () normalization is distributed:

${\mathrm{pdf}\left(Z_i\right)}^{\&prime;\&prime;}=\frac{{\mathrm{pdf}\left(Z_i\right)}^{\&prime;}}{{{\mathrm{\&Sigma;}}_i\mathrm{pdf}\left(Z_i\right)}^{\&prime;}},$

Adopt following relational expression calculating probability cumulative distribution function:

$\mathrm{cdf}\left(Z_i\right)={\mathrm{\&Sigma;}}_{j=0}^i\mathrm{pdf}{\left(Z_i\right)}^{\&prime;\&prime;}.$

3. method according to claim 2, is characterized in that, further comprises step:

Regulate exponential factor a to control the intensity that contrast promotes.

4. method according to claim 2, is characterized in that, further comprises step: image is kept away to dodge and process.

5. method according to claim 4, is characterized in that, described to image keep away dodge process comprise:

Adopt to cdf () amplitude limit, if z _i-cdf (Z _i) > T (z _i), z _i-cdf (Z _i)=T (Z _i); If z _i-cdf (Z _i) <-T (z _i), z _i-cdf (Z _it (the Z of)=- _i), wherein T (Z _i) be and z _irelevant threshold function table.

6. method according to claim 4, is characterized in that, described to image keep away dodge process comprise:

Adopt the level and smooth mode of interframe, adopt following relational expression: image is kept away to dodge and process, wherein α is interframe smoothing factor, f (Z _i) be GTG mapping function.

7. a dynamic contrast adjustment System for digital image, described system comprises:

One reading unit, for reading a two field picture of piece image or video;

One probability cumulative distribution computing unit, for calculating the pixel brightness value probability cumulative distribution function cdf () of described image;

One contrast adjustment unit, in the time that image is gray scale image, described contrast adjustment unit adopts relational expression: contrast to current gray scale image is adjusted; In the time that image is coloured image, described contrast adjustment unit adopts relational expression: contrast to current coloured image is adjusted, wherein, and z _i=f (E _i), z _ifor pixel is at exposure brightness E _ioutput pixel value, f () is linear function, Y _ibrightness value, C _iit is a passage in tri-color channels of RGB.

8. system according to claim 7, it is characterized in that, described system further comprises a probability density calculation unit and a normalization unit, described probability density computing unit is for calculating the brightness histogram of described image, obtain probability density function pdf (), described normalization unit adopts following relational expression to calculate probability density function pdf () is done to index normalization:

${\mathrm{pdf}\left(Z_i\right)}^{\&prime;}={\left(\frac{\mathrm{pdf}\left(Z_i\right)-\min \left\{\mathrm{pdf}(\&CenterDot;)\right\}}{\max \left\{\mathrm{pdf}(\&CenterDot;)\right\}-\min \left\{\mathrm{pdf}(\&CenterDot;)\right\}}\right)}^a,$ A is exponential factor;

Described normalization unit adopts following relational expression that probability density function pdf () normalization is distributed:

${\mathrm{pdf}\left(Z_i\right)}^{\&prime;\&prime;}=\frac{{\mathrm{pdf}\left(Z_i\right)}^{\&prime;}}{{{\mathrm{\&Sigma;}}_i\mathrm{pdf}\left(Z_i\right)}^{\&prime;}},$

Described probability cumulative distribution computing unit adopts following relational expression calculating probability cumulative distribution function:

$\mathrm{cdf}\left(Z_i\right)={\mathrm{\&Sigma;}}_{j=0}^i\mathrm{pdf}{\left(Z_i\right)}^{\&prime;\&prime;}.$

9. system according to claim 8, is characterized in that, described system further comprises a parameter regulon, for regulating exponential factor a to control the intensity that contrast promotes.

10. system according to claim 8, is characterized in that, described system further comprises keeps away sudden strain of a muscle processing unit, described in keep away and dodge processing unit for avoiding video playback, adjust in real time the problem of the film flicker bringing.

11. methods according to claim 10, is characterized in that, described in keep away dodge processing unit to cdf () amplitude limit to image keep away dodge process, work as z _i-cdf (Z _i) > T (z _i) time, z _i-cdf (Z _i)=T (Z _i); Work as z _i-cdf (Z _i) <-T (z _i) time, z _i-cdf (Z _it (the Z of)=- _i), wherein T (Z _i) be and z _irelevant threshold function table.

12. methods according to claim 10, is characterized in that, described in keep away and dodge processing unit and adopt interframe level and smooth mode, adopt following relational expression: image is kept away to dodge and process, wherein α is interframe smoothing factor, f (Z _i) be GTG mapping function.