编写彩色空间转换程序：YUVtoRGB

Y=+0.299R+0.587G+0.114B
U₀=0.564(B-Y)=−0.1684R−0.3316G+0.5B
V₀=0.713(R-Y)=+0.5R−0.4187G−0.0813B

所以
B-Y=U₀/0.564 B=Y+1.773U₀
R-Y=V₀/0.713 R=Y+1.403V₀
G=(Y-(0.299R+0.114B))/0.587 G=Y-0.714V₀-0.344U₀

U=U₀+128
V=V₀+128

所以
B=Y+1.773U-226.944
R=Y+1.403V-179.584
G=Y-0.714V-0.344U+135.424

yuv2rgb.cpp:

#include "stdlib.h"
#include "yuv2rgb.h"
#include <stdio.h>static float R_V01403[256],B_U01773[256], G_U_0344[256],G_V_0714[256];int YUV2RGB(int x_dim, int y_dim, void* bmp, void* rgb_out)
{static int init_done = 0;long i, j, size;unsigned char* y, * u, * v;unsigned char* r, * g, * b;size = x_dim * y_dim;if (init_done == 0){InitLookupTable();init_done = 1;}// allocate memoryy = (unsigned char*)bmp;b = (unsigned char*)rgb_out;// convert RGB to YUVfor (j = 0; j < y_dim; j++){for (i = 0; i < x_dim; i++) {g = b + 1;r = b + 2;u = y + x_dim * y_dim - (i + 1) / 2 - (j + 1)/2 * x_dim/2;v = y + x_dim * y_dim + x_dim / 2 * y_dim / 2 - (i + 1) / 2 - (j + 1)/2  * x_dim/2;int rr, gg, bb;rr= (int)(*y + R_V01403[*v]); //-179.584gg=(int)(*y + G_U_0344[*u] + G_V_0714[*v]);//+ 135.424bb=(int)(*y + B_U01773[*u]);//- 226.944*r = rr;//(unsigned char)(*y + R_V01403[*v] ); //-179.584*g = gg;// (unsigned char)(*y + G_U_0344[*u] + G_V_0714[*v]);//+ 135.424*b = bb;//(unsigned char)(*y + B_U01773[*u] );//- 226.944y++;b+=3;}}return 0;
}void InitLookupTable()
{int i;for (i = 0; i < 256; i++) R_V01403[i] = (float)1.403 * (i-128);for (i = 0; i < 256; i++) B_U01773[i] = (float)1.773 * (i-128);for (i = 0; i < 256; i++) G_U_0344[i] = (float)-0.344 * (i-128);for (i = 0; i < 256; i++) G_V_0714[i] = (float)-0.714 * (i-128);
}

main.cpp:

#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#include "yuv2rgb.h"
#pragma warning(disable:4996)
#define u_int8_t    unsigned __int8
#define u_int       unsigned __int32
#define u_int32_t   unsigned __int32
#define FALSE       false
#define TRUE        trueint main(int argc, char** argv)
{/* variables controlable from command line */u_int frameWidth = 352;          /* --width=<uint> */u_int frameHeight = 240;        /* --height=<uint> */bool flip = TRUE;              /* --flip */unsigned int i;/* internal variables */char* rgbFileName = NULL;char* yuvFileName = NULL;FILE* rgbFile = NULL;FILE* yuvFile = NULL;u_int8_t* yuvBuf = NULL;u_int8_t* rgbBuf = NULL;u_int32_t videoFramesWritten = 0;/* begin process command line *//* point to the specified file names */yuvFileName = argv[1];rgbFileName = argv[2];frameWidth = atoi(argv[3]);frameHeight = atoi(argv[4]);/* open the RGB file */yuvFile = fopen(yuvFileName, "rb");if (yuvFile == NULL){printf("cannot find yuv file\n");exit(1);}else{printf("The input yuv file is %s\n", yuvFileName);}/* open the RAW file */rgbFile = fopen(rgbFileName, "wb");if (rgbFile == NULL){printf("cannot find rgb file\n");exit(1);}else{printf("The output rgb file is %s\n", rgbFileName);}/* get an input buffer for a frame */yuvBuf = (u_int8_t*)malloc(frameWidth * frameHeight * 1.5);/* get the output buffers for a frame */rgbBuf = (u_int8_t*)malloc(frameWidth * frameHeight*3);if (yuvBuf == NULL || rgbBuf == NULL){printf("no enough memory\n");exit(1);}while (fread(yuvBuf, 1, frameWidth * frameHeight * 1.5, yuvFile)){if (YUV2RGB(frameWidth, frameHeight, yuvBuf, rgbBuf)){printf("error");return 0;}for (i = 0; i < frameWidth * frameHeight*3; i++){if (rgbBuf[i] < 0) rgbBuf[i] = 0;if (rgbBuf[i] > 255) rgbBuf[i] = 255;}
/*for (i = 0; i < frameWidth * frameHeight / 4; i++){if (uBuf[i] < 16) uBuf[i] = 16;if (uBuf[i] > 240) uBuf[i] = 240;if (vBuf[i] < 16) vBuf[i] = 16;if (vBuf[i] > 240) vBuf[i] = 240;}fwrite(bBuf, 1, frameWidth * frameHeight, yuvFile);fwrite(gBuf, 1, (frameWidth * frameHeight) / 4, yuvFile);fwrite(rBuf, 1, (frameWidth * frameHeight) / 4, yuvFile);*/fwrite(rgbBuf, 1, frameWidth*frameHeight*3, rgbFile);printf("\r...%d", ++videoFramesWritten);}printf("\n%u %ux%u video frames written\n",videoFramesWritten, frameWidth, frameHeight);/* cleanup */fclose(rgbFile);fclose(yuvFile);return(0);
}

yuv2rgb.h

#pragma once
int YUV2RGB(int x_dim, int y_dim, void* bmp, void* rgb_out);void InitLookupTable();

图片出现以下错误：

观察正确的yuv与rgb大小和获得的yuv与rgb大小：

正确值：

获得值：

对比可知获得的u、v值异常偏小，导致rgb图像错误。
检验得偏移量错误。

改正偏移量部分：

     for (j = 0; j < y_dim; j++){for (i = 0; i < x_dim; i++) {g = b + 1;r = b + 2;u = y + x_dim * y_dim - (i + 1) / 2 - j * 2 * x_dim / 2 + (j + 1) / 2 * x_dim / 2;v = y + x_dim * y_dim + x_dim / 2 * y_dim / 2 - (i + 1) / 2 - j * 2 * x_dim / 2 + (j + 1) / 2 * x_dim / 2;int rr, gg, bb;rr= (int)(*y + R_V01403[*v]); gg=(int)(*y + G_U_0344[*u] + G_V_0714[*v]);bb=(int)(*y + B_U01773[*u]);*r=rr;*g=gg;*b=bb;y++;b+=3;}}

改正后结果：

有部分像素值越界。

将值限定在0~255：

             rr= (int)(*y + R_V01403[*v]); //-179.584gg=(int)(*y + G_U_0344[*u] + G_V_0714[*v]);//+ 135.424bb=(int)(*y + B_U01773[*u]);//- 226.944if (rr < 0) rr = 0;if (rr > 255) rr = 255;if (gg < 0) gg = 0;if (gg > 255) gg = 255;if (bb < 0) bb = 0;if (bb > 255) bb = 255;*r = rr;*g = gg;*b = bb;

改正后图像：

变换前yuv图像：

该yuv文件为4:2:0格式，u与v的数量为y的1/4，由总数1/4的u与v生成r、g、b会带来一定误差，同时进行转换计算时由小数变为整数也会产生一定误差，但只观察图像时难以辨别。