YUV & RGB 相互转换公式
YCbCr 的 Y 与 YUV 中的 Y 含义一致，Cb 和 Cr 与 UV 同样都指色彩，Cb 指蓝色色度，Cr 指红色色度，在应用上很广泛，JPEG、MPEG、DVD、摄影机、数字电视等皆采此一格式。
因此一般俗称的 YUV 大多是指 YCbCr 。
- RGB to YUV（YCbCr）
RGB 范围 [0,255]，Y 范围 [16,235] ，UV 范围 [16,239]。如果计算结果超过了取值范围要进行截取。
Y = 0.257*R + 0.504*G + 0.098*B + 16;
U = -0.148*R - 0.291*G + 0.439*B + 128;
V = 0.439*R - 0.368*G - 0.071*B + 128;
- YUV（YCbCr）to RGB
RGB 范围 [0,255]，Y 范围 [16,235] ，UV 范围 [16,239]。如果计算结果超过了取值范围要进行截取。
R = 1.164*(Y - 16) + 1.596*(V - 128);
G = 1.164*(Y - 16) - 0.813*(V - 128) - 0.391*(U - 128);
B = 1.164*(Y - 16) + 2.018*(U - 128);
FFmpeg 工具的辅助
FFmpeg 将 之前生成的彩虹图 BMP 转成 YUV 格式的文件、RGB 格式的文件
ffmpeg -i rainbow.bmp -video_size 700x700 -pix_fmt yuv444p rainbow-yuv444p.yuv
ffmpeg -i rainbow.bmp -video_size 700x700 -pix_fmt rgb24 rainbow-rgb24.rgb
FFplay 查看生成的 YUV 格式的文件、RGB 格式的文件
ffplay -f rawvideo -pix_fmt yuv444p -video_size 700x700 rainbow-yuv444p.yuv
ffplay -f rawvideo -pix_fmt rgb24 -video_size 700x700 rainbow-rgb24.rgb
用代码实现 RGB & YUV 转换
RGB -> YUV
将 FFmpeg 生成的 RGB24 格式转换成 YUV444P 格式。
[rainbow-rgb24.rgb] -> [rainbow-rgb24-to-yuv444p.yuv]
#include <stdio.h>
#include <string.h>
#include <math.h>
// 彩虹的七种颜色
u_int32_t rainbowColors[] = {
0XFF0000, // 红
0XFFA500, // 橙
0XFFFF00, // 黄
0X00FF00, // 绿
0X007FFF, // 青
0X0000FF, // 蓝
0X8B00FF // 紫
};
u_int8_t bound(u_int8_t start, int value, u_int8_t end) {
if(value <= start) {
return start;
}
if(value >= end) {
return end;
}
return value;
}
void rgbToYuv(u_int8_t R, u_int8_t G, u_int8_t B, u_int8_t *Y, u_int8_t *U, u_int8_t *V) {
int y_val = (int)round(0.257*R + 0.504*G + 0.098*B + 16);
int u_val = (int)round(-0.148*R - 0.291*G + 0.439*B + 128);
int v_val = (int)round(0.439*R - 0.368*G - 0.071*B + 128);
*Y = bound(16, y_val, 235);
*U = bound(16, u_val, 239);
*V = bound(16, v_val, 239);
}
void rgb24ToYuv444p(const u_int8_t *rgb24Data, u_int8_t *yuv444pData, int width, int height) {
int8_t yuv_y[width*height];
int8_t yuv_u[width*height];
int8_t yuv_v[width*height];
for (int i = 0; i < width; ++i) {
for (int j = 0; j < height; ++j) {
u_int8_t Y, U, V;
u_int8_t R, G, B;
int currentRGBIndex = 3*(i*height+j);
R = rgb24Data[currentRGBIndex];
G = rgb24Data[currentRGBIndex+1];
B = rgb24Data[currentRGBIndex+2];
rgbToYuv(R, G, B, &Y, &U, &V);
int currentYUVIndex = i*height+j;
yuv_y[currentYUVIndex] = Y;
yuv_u[currentYUVIndex] = U;
yuv_v[currentYUVIndex] = V;
}
}
memcpy(yuv444pData, yuv_y, sizeof(yuv_y));
memcpy(yuv444pData + sizeof(yuv_y), yuv_u, sizeof(yuv_u));
memcpy(yuv444pData + sizeof(yuv_y) + sizeof(yuv_u), yuv_v, sizeof(yuv_v));
}
int main() {
int width = 700, height = 700;
u_int8_t yuv444pData[width*height*3];
u_int8_t rgb24Data[width*height*3];
FILE *rgb24File = fopen("/Users/staff/Desktop/rainbow-rgb24.rgb", "rb");
fread(rgb24Data, sizeof(rgb24Data), 1, rgb24File);
rgb24ToYuv444p(rgb24Data, yuv444pData, width, height);
FILE *yuv444pFile = fopen("/Users/ff/Desktop/rainbow-rgb24-to-yuv444p.yuv", "wb");
fwrite(yuv444pData, sizeof(yuv444pData), 1, yuv444pFile);
fclose(rgb24File);
fclose(yuv444pFile);
return 0;
}
ffplay -f rawvideo -pix_fmt rgb24 -video_size 700x700 rainbow-rgb24.rgb
ffplay -f rawvideo -pix_fmt yuv444p -video_size 700x700 rainbow-rgb24-to-yuv444p.yuv
YUV -> RGB
将 FFmpeg 生成的 YUV444P 格式转换成 RGB24 格式。
[rainbow-yuv444p.yuv] -> [rainbow-yuv444p-to-rgb24.rgb]
#include <stdio.h>
#include <math.h>
u_int8_t bound(u_int8_t start, int value, u_int8_t end) {
if(value <= start) {
return start;
}
if(value >= end) {
return end;
}
return value;
}
void yuv444pToRGB(u_int8_t *yuv444pData,u_int8_t *rgb24Data, int width, int height) {
u_int8_t *srcY = yuv444pData, *srcU = srcY + width * height, *srcV = srcU + width * height;
for(int i = 0 ; i < height ; i ++) {
for (int j = 0; j < width; j++) {
int currentYUVIndex = i * height + j;
u_int8_t Y = srcY[currentYUVIndex], U = srcU[currentYUVIndex], V = srcV[currentYUVIndex];
int r_val = (int)round(1.164*(Y-16)+1.596*(V-128));
int g_val = (int)round(1.164*(Y-16)-0.813*(V-128)-0.391*(U-128));
int b_val = (int)round(1.164*(Y-16)+2.018*(U-128));
int currentRGBIndex = 3*(i * width + j);
rgb24Data[currentRGBIndex] = bound(0, r_val, 255);
rgb24Data[currentRGBIndex+1] = bound(0, g_val, 255);
rgb24Data[currentRGBIndex+2] = bound(0, b_val, 255);
}
}
}
int main() {
int width = 700, height = 700;
u_int8_t yuv444pData[width*height*3];
u_int8_t rgb24Data[width*height*3];
FILE *yuv444pFile = fopen("/Users/staff/Desktop/rainbow-yuv444p.yuv", "rb");
fread(yuv444pData, sizeof(yuv444pData), 1, yuv444pFile);
yuv444pToRGB(yuv444pData, rgb24Data, width, height);
FILE *rgb24File = fopen("/Users/staff/Desktop/rainbow-yuv444p-to-rgb24.rgb", "wb");
fwrite(rgb24Data, sizeof(rgb24Data), 1, rgb24File);
fclose(yuv444pFile);
fclose(rgb24File);
return 0;
}
ffplay -f rawvideo -pix_fmt yuv444p -video_size 700x700 rainbow-yuv444p.yuv
ffplay -f rawvideo -pix_fmt rgb24 -video_size 700x700 rainbow-yuv444p-to-rgb24.rgb
使用色彩丰富的图片验证
准备一张手机拍摄的 Disney.png
ffmpeg -i Disney.png -video_size 700x700 -pix_fmt yuv444p Disney-yuv444p.yuv
ffmpeg -i Disney.png -video_size 700x700 -pix_fmt rgb24 Disney-rgb24.rgb
ffplay -f rawvideo -pix_fmt yuv444p -video_size 700x700 Disney-yuv444p.yuv
ffplay -f rawvideo -pix_fmt rgb24 -video_size 700x700 Disney-rgb24.rgb
使用上面的代码进行转换后得到 Disney-rgb24-to-yuv444p.yuv Disney-yuv444p-to-rgb24.rgb
Congratulations!
参考资料：
YUV格式学习：YUV420P、YV12、NV12、NV21格式转换成RGB24
YUV420与YUV444互转，YUV420与YUV444读取和保存，YUV的显示和播放功能
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