2022年c语言CLAHE算法 .pdf

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1、CLAHE 算法*Contrast Limited Adaptive Histogram Equalization*by Karel Zuiderveld,karelcv.ruu.nl*in Graphics Gems IV,Academic Press,1994*These functions implement Contrast Limited Adaptive Histogram Equalization.*The main routine(CLAHE)expects an input image that is stored contiguously in*memory;the CLA

2、HE output image overwrites the original input image and has the*same minimum and maximum values(which must be provided by the user).*This implementation assumes that the X-and Y image resolutions are an integer*multiple of the X-and Y sizes of the contextual regions.A check on various other*error co

3、nditions is performed.*#define the symbol BYTE_IMAGE to make this implementation suitable for*8-bit images.The maximum number of contextual regions can be redefined*by changing uiMAX_REG_X and/or uiMAX_REG_Y;the use of more than 256*contextual regions is not recommended.*The code is ANSI-C and is al

4、so C+compliant.*Author:Karel Zuiderveld,Computer Vision Research Group,*Utrecht,The Netherlands(karelcv.ruu.nl)*/#ifdef BYTE_IMAGE typedef unsigned char kz_pixel_t;/*for 8 bit-per-pixel images*/#define uiNR_OF_GREY(256)#else typedef unsigned short kz_pixel_t;/*for 12 bit-per-pixel images(default)*/#

5、define uiNR_OF_GREY(4096)#endif/*Prototype of CLAHE function.Put this in a separate include file.*/int CLAHE(kz_pixel_t*pImage,unsigned int uiXRes,unsigned int uiYRes,kz_pixel_t Min,kz_pixel_t Max,unsigned int uiNrX,unsigned int uiNrY,unsigned int uiNrBins,float fCliplimit);/*Local prototypes*/stati

6、c void ClipHistogram(unsigned long*,unsigned int,unsigned long);static void MakeHistogram(kz_pixel_t*,unsigned int,unsigned int,unsigned int,unsigned long*,unsigned int,kz_pixel_t*);static void MapHistogram(unsigned long*,kz_pixel_t,kz_pixel_t,unsigned int,unsigned long);名师资料总结-精品资料欢迎下载-名师精心整理-第 1 页

7、，共 7 页 -static void MakeLut(kz_pixel_t*,kz_pixel_t,kz_pixel_t,unsigned int);static void Interpolate(kz_pixel_t*,int,unsigned long*,unsigned long*,unsigned long*,unsigned long*,unsigned int,unsigned int,kz_pixel_t*);/*Start of actual code*/#include /*To get prototypes of malloc()and free()*/const uns

8、igned int uiMAX_REG_X=16;/*max.#contextual regions in x-direction*/const unsigned int uiMAX_REG_Y=16;/*max.#contextual regions in y-direction*/*main function CLAHE*/int CLAHE(kz_pixel_t*pImage,unsigned int uiXRes,unsigned int uiYRes,kz_pixel_t Min,kz_pixel_t Max,unsigned int uiNrX,unsigned int uiNrY

9、,unsigned int uiNrBins,float fCliplimit)/*pImage-Pointer to the input/output image*uiXRes-Image resolution in the X direction*uiYRes-Image resolution in the Y direction*Min-Minimum greyvalue of input image(also becomes minimum of output image)*Max-Maximum greyvalue of input image(also becomes maximu

10、m of output image)*uiNrX-Number of contextial regions in the X direction(min 2,max uiMAX_REG_X)*uiNrY-Number of contextial regions in the Y direction(min 2,max uiMAX_REG_Y)*uiNrBins-Number of greybins for histogram(dynamic range)*float fCliplimit-Normalized cliplimit(higher values give more contrast

11、)*The number of effective greylevels in the output image is set by uiNrBins;selecting*a small value(eg.128)speeds up processing and still produce an output image of*good quality.The output image will have the same minimum and maximum value as the input*image.A clip limit smaller than 1 results in st

12、andard(non-contrast limited)AHE.*/unsigned int uiX,uiY;/*counters*/unsigned int uiXSize,uiYSize,uiSubX,uiSubY;/*size of context.reg.and subimages*/unsigned int uiXL,uiXR,uiYU,uiYB;/*auxiliary variables interpolation routine*/unsigned long ulClipLimit,ulNrPixels;/*clip limit and region pixel count*/k

13、z_pixel_t*pImPointer;/*pointer to image*/kz_pixel_t aLUTuiNR_OF_GREY;/*lookup table used for scaling of input image*/unsigned long*pulHist,*pulMapArray;/*pointer to histogram and mappings*/unsigned long*pulLU,*pulLB,*pulRU,*pulRB;/*auxiliary pointers interpolation*/if(uiNrX uiMAX_REG_X)return-1;/*#o

14、f regions x-direction too large*/if(uiNrY uiMAX_REG_Y)return-2;/*#of regions y-direction too large*/if(uiXRes%uiNrX)return-3;/*x-resolution no multiple of uiNrX*/名师资料总结-精品资料欢迎下载-名师精心整理-第 2 页，共 7 页 -if(uiYRes&uiNrY)return-4;/*y-resolution no multiple of uiNrY*/if(Max=uiNR_OF_GREY)return-5;/*maximum t

15、oo large*/if(Min=Max)return-6;/*minimum equal or larger than maximum*/if(uiNrX 2|uiNrY 0.0)/*Calculate actual cliplimit*/ulClipLimit=(unsigned long)(fCliplimit*(uiXSize*uiYSize)/uiNrBins);ulClipLimit=(ulClipLimit 1UL)?1UL:ulClipLimit;else ulClipLimit=1UL14;/*Large value,do not clip(AHE)*/MakeLut(aLU

16、T,Min,Max,uiNrBins);/*Make lookup table for mapping of greyvalues*/*Calculate greylevel mappings for each contextual region*/for(uiY=0,pImPointer=pImage;uiY uiNrY;uiY+)for(uiX=0;uiX uiNrX;uiX+,pImPointer+=uiXSize)pulHist=&pulMapArrayuiNrBins*(uiY*uiNrX+uiX);MakeHistogram(pImPointer,uiXRes,uiXSize,ui

17、YSize,pulHist,uiNrBins,aLUT);ClipHistogram(pulHist,uiNrBins,ulClipLimit);MapHistogram(pulHist,Min,Max,uiNrBins,ulNrPixels);pImPointer+=(uiYSize-1)*uiXRes;/*skip lines,set pointer*/*Interpolate greylevel mappings to get CLAHE image*/for(pImPointer=pImage,uiY=0;uiY 1;uiYU=0;uiYB=0;else if(uiY=uiNrY)/*

18、special case:bottom row*/uiSubY=uiYSize 1;uiYU=uiNrY-1;uiYB=uiYU;else /*default values*/uiSubY=uiYSize;uiYU=uiY-1;uiYB=uiYU+1;名师资料总结-精品资料欢迎下载-名师精心整理-第 3 页，共 7 页 -for(uiX=0;uiX 1;uiXL=0;uiXR=0;else if(uiX=uiNrX)/*special case:right column*/uiSubX=uiXSize 1;uiXL=uiNrX-1;uiXR=uiXL;else /*default values

19、*/uiSubX=uiXSize;uiXL=uiX-1;uiXR=uiXL+1;pulLU=&pulMapArrayuiNrBins*(uiYU*uiNrX+uiXL);pulRU=&pulMapArrayuiNrBins*(uiYU*uiNrX+uiXR);pulLB=&pulMapArrayuiNrBins*(uiYB*uiNrX+uiXL);pulRB=&pulMapArrayuiNrBins*(uiYB*uiNrX+uiXR);Interpolate(pImPointer,uiXRes,pulLU,pulRU,pulLB,pulRB,uiSubX,uiSubY,aLUT);pImPoi

20、nter+=uiSubX;/*set pointer on next matrix*/pImPointer+=(uiSubY-1)*uiXRes;free(pulMapArray);/*free space for histograms*/return 0;/*return status OK*/void ClipHistogram(unsigned long*pulHistogram,unsigned int uiNrGreylevels,unsigned long ulClipLimit)/*This function performs clipping of the histogram

21、and redistribution of bins.*The histogram is clipped and the number of excess pixels is counted.Afterwards*the excess pixels are equally redistributed across the whole histogram(providing*the bin count is smaller than the cliplimit).*/unsigned long*pulBinPointer,*pulEndPointer,*pulHisto;unsigned lon

22、g ulNrExcess,ulUpper,ulBinIncr,ulStepSize,i;long lBinExcess;ulNrExcess=0;pulBinPointer=pulHistogram;for(i=0;i 0)ulNrExcess+=lBinExcess;/*excess in current bin*/;/*Second part:clip histogram and redistribute excess pixels in each bin*/名师资料总结-精品资料欢迎下载-名师精心整理-第 4 页，共 7 页 -ulBinIncr=ulNrExcess/uiNrGreyl

23、evels;/*average binincrement*/ulUpper=ulClipLimit-ulBinIncr;/*Bins larger than ulUpper set to cliplimit*/for(i=0;i ulClipLimit)pulHistogrami=ulClipLimit;/*clip bin*/else if(pulHistogrami ulUpper)/*high bin count*/ulNrExcess-=(ulClipLimit-pulHistogrami);pulHistogrami=ulClipLimit;else /*low bin count*

24、/ulNrExcess-=ulBinIncr;pulHistogrami+=ulBinIncr;while(ulNrExcess)/*Redistribute remaining excess*/pulEndPointer=&pulHistogramuiNrGreylevels;pulHisto=pulHistogram;while(ulNrExcess&pulHisto pulEndPointer)ulStepSize=uiNrGreylevels/ulNrExcess;if(ulStepSize 1)ulStepSize=1;/*stepsize at least 1*/for(pulBi

25、nPointer=pulHisto;pulBinPointer pulEndPointer&ulNrExcess;pulBinPointer+=ulStepSize)if(*pulBinPointer ulClipLimit)(*pulBinPointer)+;ulNrExcess-;/*reduce excess*/pulHisto+;/*restart redistributing on other bin location*/void MakeHistogram(kz_pixel_t*pImage,unsigned int uiXRes,unsigned int uiSizeX,unsi

26、gned int uiSizeY,unsigned long*pulHistogram,unsigned int uiNrGreylevels,kz_pixel_t*pLookupTable)/*This function classifies the greylevels present in the array image into*a greylevel histogram.The pLookupTable specifies the relationship*between the greyvalue of the pixel(typically between 0 and 4095)

27、and*the corresponding bin in the histogram(usually containing only 128 bins).*/kz_pixel_t*pImagePointer;unsigned int i;名师资料总结-精品资料欢迎下载-名师精心整理-第 5 页，共 7 页 -for(i=0;i uiNrGreylevels;i+)pulHistogrami=0L;/*clear histogram*/for(i=0;i uiSizeY;i+)pImagePointer=&pImageuiSizeX;while(pImage pImagePointer)pulH

28、istogrampLookupTable*pImage+;pImagePointer+=uiXRes;pImage=&pImagePointer-uiSizeX;void MapHistogram(unsigned long*pulHistogram,kz_pixel_t Min,kz_pixel_t Max,unsigned int uiNrGreylevels,unsigned long ulNrOfPixels)/*This function calculates the equalized lookup table(mapping)by*cumulating the input his

29、togram.Note:lookup table is rescaled in range Min.Max.*/unsigned int i;unsigned long ulSum=0;const float fScale=(float)(Max-Min)/ulNrOfPixels;const unsigned long ulMin=(unsigned long)Min;for(i=0;i Max)pulHistogrami=Max;void MakeLut(kz_pixel_t*pLUT,kz_pixel_t Min,kz_pixel_t Max,unsigned int uiNrBins)

30、/*To speed up histogram clipping,the input image Min,Max is scaled down to*0,uiNrBins-1.This function calculates the LUT.*/int i;const kz_pixel_t BinSize=(kz_pixel_t)(1+(Max-Min)/uiNrBins);for(i=Min;i=Max;i+)pLUTi=(i-Min)/BinSize;void Interpolate(kz_pixel_t*pImage,int uiXRes,unsigned long*pulMapLU,u

31、nsigned long*pulMapRU,unsigned long*pulMapLB,unsigned long*pulMapRB,unsigned int uiXSize,unsigned int uiYSize,kz_pixel_t*pLUT)/*pImage-pointer to input/output image*uiXRes-resolution of image in x-direction*pulMap*-mappings of greylevels from histograms 名师资料总结-精品资料欢迎下载-名师精心整理-第 6 页，共 7 页 -*uiXSize-u

32、iXSize of image submatrix*uiYSize-uiYSize of image submatrix*pLUT-lookup table containing mapping greyvalues to bins*This function calculates the new greylevel assignments of pixels within a submatrix*of the image with size uiXSize and uiYSize.This is done by a bilinear interpolation*between four di

33、fferent mappings in order to eliminate boundary artifacts.*It uses a division;since division is often an expensive operation,I added code to*perform a logical shift instead when feasible.*/const unsigned int uiIncr=uiXRes-uiXSize;/*Pointer increment after processing row*/kz_pixel_t GreyValue;unsigne

34、d int uiNum=uiXSize*uiYSize;/*Normalization factor*/unsigned int uiXCoef,uiYCoef,uiXInvCoef,uiYInvCoef,uiShift=0;if(uiNum&(uiNum-1)/*If uiNum is not a power of two,use division*/for(uiYCoef=0,uiYInvCoef=uiYSize;uiYCoef uiYSize;uiYCoef+,uiYInvCoef-,pImage+=uiIncr)for(uiXCoef=0,uiXInvCoef=uiXSize;uiXCoef=1)uiShift+;/*Calculate 2log of uiNum*/for(uiYCoef=0,uiYInvCoef=uiYSize;uiYCoef uiYSize;uiYCoef+,uiYInvCoef-,pImage+=uiIncr)for(uiXCoef=0,uiXInvCoef=uiXSize;uiXCoef uiShift);名师资料总结-精品资料欢迎下载-名师精心整理-第 7 页，共 7 页 -