关于opencv中cvtcolor函数的code参数用CV_BGR2YUV与CV

根据Opencv中cvtcolor函数的源码描述，,参数CV_BGR2YCrCb用的系数为[1868, 9617, 4899, 11682, 9241]，而参数CV_BGR2YUV对应的系数只是将CV_BGR2YCrCb对应的系数中1868和4899互换而已，

，系数介绍，可参考http://baike.baidu.com/view/640197.htm?fr=aladdin

经过对源码的阅读，对源码做如下改写：

</pre><pre name="code" class="cpp">enum
{R2Y = 4899,G2Y = 9617,B2Y = 1868,
};

inline void RGB2YCrCb_i(int blueIdx, int coeffs[], const int* _coeffs)
{static const int coeffs0[] = {R2Y, G2Y, B2Y, 11682, 9241};//CV_BGR2YUV对应的系数memcpy(coeffs, _coeffs ? _coeffs : coeffs0, 5*sizeof(coeffs[0]));if(blueIdx==0) std::swap(coeffs[0], coeffs[2]);//对应的code 为CV_BRG2YCrCv时, 将CV_BGR2YUV对应的系数的R2y(4899)与B2y(1868)对应的值互换
}

inline void Operater_YCrCb_i(unsigned char* src,int srccn, int blueId,  int coeffs[], unsigned char* dst, int n)
{int scn = srccn, bidx = blueId;int C0 = coeffs[0], C1 = coeffs[1], C2 = coeffs[2], C3 = coeffs[3], C4 = coeffs[4];ColorChannel cc;int delta = cc.half()*(1<<yuv_shift);n *= 3;for (int i=0; i<n; i +=  3,  src += scn){int Y = CV_DESCALE(src[0]*C0 + src[1]*C1 + src[2]*C2, yuv_shift);int Cr = CV_DESCALE((src[bidx^2] - Y)*C3 + delta, yuv_shift);int Cb = CV_DESCALE((src[bidx] - Y)*C4 + delta, yuv_shift);dst[i] = (unsigned char)(Y);dst[i+1] = (unsigned char)(Cr);dst[i+2] = (unsigned char)(Cb);}}void CvtColor_YCrCb_i(unsigned char* src, int sstep, unsigned char* dst, int dstep, int nWidth, int nHeight, int nChannel,  int code, int dcn)
{assert(nWidth >=0 && nHeight >= 0);int scn = nChannel, bidx;unsigned char* src_ptr = NULL;unsigned char* dst_ptr = NULL;switch(code){case CV_BGR2YCrCb: case CV_RGB2YCrCb:case CV_BGR2YUV: case CV_RGB2YUV:assert(scn == 3 || scn == 4);bidx = code == CV_BGR2YCrCb || code == CV_RGB2YUV ? 0 : 2;static const int yuv_i[]= {B2Y, G2Y, R2Y, 8061, 14369};const int* coeffs_i = code == CV_BGR2YCrCb || code == CV_RGB2YCrCb ? 0 : yuv_i;for (int row = 0; row < nHeight; row++){src_ptr = (unsigned char*)(src + row*sstep);dst_ptr = (unsigned char*)(dst + row*dstep);for (int col = 0; col < nWidth; col++){int coeffs[5];RGB2YCrCb_i(bidx, coeffs,coeffs_i );Operater_YCrCb_i(src_ptr, scn, bidx, coeffs, dst_ptr, nWidth*nHeight/(double(1<<16)));src_ptr += 3;dst_ptr += 3;}}}
}

该后的代码去掉了源码中的并行运算部分，该代码没有考虑运算效率。

维基百科中关于rgb->yuv 和rgb->ycbcr的具体介绍为：

详细内容可参考 http://zh.wikipedia.org/wiki/YUV

及http://blog.sina.com.cn/s/blog_4665b35b0100vf6r.html

附整个改写的代码部分：

#ifndef _RGB2YUV_H_
#define _RGB2YUV_H_#include "opencv2/core/core.hpp"
#include "opencv2/imgproc/imgproc.hpp"#include <math.h>
#include <assert.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <limits.h>
#include <float.h>using namespace std;
using namespace cv;#undef R2Y
#undef G2Y
#undef B2Y#define  CV_DESCALE(x,n)     (((x) + (1 << ((n)-1))) >> (n))enum
{yuv_shift = 14,xyz_shift = 12,R2Y = 4899,G2Y = 9617,B2Y = 1868,BLOCK_SIZE = 256
};struct ColorChannel
{typedef float worktype_f;static uchar max() { return std::numeric_limits<uchar>::max(); }static uchar half() { return (uchar)(max()/2 + 1); }
};inline void RGB2YCrCb_i( int blueId, int coeffs[], const int* _coeffs);
inline void Operater_YCrCb_i(unsigned char* src,int srccn, int blueId,  int coeffs[], unsigned char* dst, int n);void CvtColor_YCrCb_i(unsigned char* src, int sstep, unsigned char* dst, int dstep, int nWidth, int nHeight, int nChannel,  int code, int dcn = 0);#endif

#include "rgb2yuv.h"inline void RGB2YCrCb_i(int blueIdx, int coeffs[], const int* _coeffs)
{static const int coeffs0[] = {R2Y, G2Y, B2Y, 11682, 9241};//CV_BGR2YUV对应的系数memcpy(coeffs, _coeffs ? _coeffs : coeffs0, 5*sizeof(coeffs[0]));if(blueIdx==0) std::swap(coeffs[0], coeffs[2]);//对应的code 为CV_BRG2YCrCv时, 将CV_BGR2YUV对应的系数的R2y(4899)与B2y(1868)对应的值互换
}inline void Operater_YCrCb_i(unsigned char* src,int srccn, int blueId,  int coeffs[], unsigned char* dst, int n)
{int scn = srccn, bidx = blueId;int C0 = coeffs[0], C1 = coeffs[1], C2 = coeffs[2], C3 = coeffs[3], C4 = coeffs[4];ColorChannel cc;int delta = cc.half()*(1<<yuv_shift);n *= 3;for (int i=0; i<n; i +=  3,  src += scn){int Y = CV_DESCALE(src[0]*C0 + src[1]*C1 + src[2]*C2, yuv_shift);int Cr = CV_DESCALE((src[bidx^2] - Y)*C3 + delta, yuv_shift);int Cb = CV_DESCALE((src[bidx] - Y)*C4 + delta, yuv_shift);dst[i] = (unsigned char)(Y);dst[i+1] = (unsigned char)(Cr);dst[i+2] = (unsigned char)(Cb);}}void CvtColor_YCrCb_i(unsigned char* src, int sstep, unsigned char* dst, int dstep, int nWidth, int nHeight, int nChannel,  int code, int dcn)
{assert(nWidth >=0 && nHeight >= 0);int scn = nChannel, bidx;unsigned char* src_ptr = NULL;unsigned char* dst_ptr = NULL;switch(code){case CV_BGR2YCrCb: case CV_RGB2YCrCb:case CV_BGR2YUV: case CV_RGB2YUV:assert(scn == 3 || scn == 4);bidx = code == CV_BGR2YCrCb || code == CV_RGB2YUV ? 0 : 2;static const int yuv_i[]= {B2Y, G2Y, R2Y, 8061, 14369};const int* coeffs_i = code == CV_BGR2YCrCb || code == CV_RGB2YCrCb ? 0 : yuv_i;for (int row = 0; row < nHeight; row++){src_ptr = (unsigned char*)(src + row*sstep);dst_ptr = (unsigned char*)(dst + row*dstep);for (int col = 0; col < nWidth; col++){int coeffs[5];RGB2YCrCb_i(bidx, coeffs,coeffs_i );Operater_YCrCb_i(src_ptr, scn, bidx, coeffs, dst_ptr, nWidth*nHeight/(double(1<<16)));src_ptr += 3;dst_ptr += 3;}}}
}

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关于opencv中cvtcolor函数的code参数用CV_BGR2YUV与CV_BGR2YCrCb的了解

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