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

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：

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<=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 
#include 
#include 
#include 
#include 
#include 
#include 

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::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<=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;
				}
			}
			
	}
}