图片格式之YUV420 转RGB格式（含代码）

在数字图像处理种YUV格式也是我们经常遇到，与RGB一样也是一种编码格式，开始主要用于电视系统以及模拟视频领域。YUV，分为三个分量，“Y”表示明亮度（Luminance或Luma），也就是灰度值；而“U”和“V” 表示的则是色度（Chrominance或Chroma），作用是描述影像色彩及饱和度，用于指定像素的颜色。如果没用UV信息，只有Y信息，也可以进行成像不过只是黑白的，这样就能很好解决彩色电视与黑白电视的兼容问题，与RGB相比，YUV占用带宽较少，目前摄像头输出格式普遍采用YUV格式。

YUV格式

目前主流的YUV格式有三种：YUV4：4：4， YUV 4:2:2,以及YUV4：2：0，其相应的格式如下：

1：YUV 4:4:4采样，每一个Y对应一组UV分量。

2：YUV 4:2:2采样，每两个Y共用一组UV分量。

3：YUV 4:2:0采样，每四个Y共用UV分量。

其分布格式如下：

 限于篇幅原因，先介绍YUV420格式，其他格式下节再介绍。

YUV类型

首先介绍下基础知识，YUV格式为两大类:plannar 和 packed.

1:plannar 的YUV格式，是先连续存储所有像素的Y，然后紧接着存储所有像素点的U，最后是所有像素点的V(即YYYYUUUUVVVV)或者还有其他方式先Y再V再U(即YYYYYYYVVVVVVUUUUUU)

2: packed格式，每个像素点的YUV连续交替存储（如YUVYUV, YYUVYYUV等）。

YUV420存储格式 

 YUV420格式由上述描述可知4个Y对应一个UV分量，基本是采样plannar格式存储（笔者学识较短，Packed的YUV420格式不知道有没有，还未见过）。Plannar格式先排所有Y分量然后按照UV排版格式，主要分为如下集中：

YV12，YU12格式(YUV420P)

YV12和YU12格式属于YUV420格式，其中Cr和Cb分别代表U，V分量 ，其存储格式是先排Y分量再分别排UV分量。

UV先后顺序不一样。YV12格式为YYYYYVVVVVVUUUUU, YU12为YYYYUUUUUUUVVVVVVV,可以用如下所图表示：

YV12
YV12

 

YU12

NV12、NV21（YUV420SP)

 

NV12和NV21是YUV420的另外两种格式，先排所有Y,然后UV交替排布。NV21格式为YYYYYYVUVUVU,

NV12为YYYYYYUVUVUV,通常 NV21和NV12也被称为YUV420SP。

NV21
NV12

 

YUV420转RGB实现方法 

方法一：

YUV420 转RGB有很多方法，网上大部分的方法按照以下公式来进行转换（实际效果参数可调）：

  R = Y + 1.402* (V - 128); //R
             G = Y - 0.34413 * (U - 128) - 0.71414 * (V - 128); //G
            B = Y + 1.772 * (U - 128); //B

以YUV420SP为例，转换成RGB代码如下：

  1. void ConvertYUV420SPToRGB(unsigned char *Src, unsigned char *Dest, int ImageWidth, int ImageHeight)
  2. {
  3.     int total = ImageWidth * ImageHeight;
  4.     unsigned char *ybase = Src;
  5.     unsigned char *ubase = &Src[total];
  6.     unsigned int index = 0;
  7.     for (int y = 0; y < ImageHeight ; y++) {
  8.         for (int x = 0; x < ImageWidth; x++) {
  9.             //YYYYYYYYVUVU
  10.             u_char Y = ybase[x + y * ImageWidth];
  11.             u_char U = ubase[y / 2 * ImageWidth + (x / 2) * 2 + 1];
  12.             u_char V = ubase[y / 2 * ImageWidth + (x / 2) * 2];
  13.  
  14.             Dest[index++] = Y + 1.402* (V - 128); //R
  15.             Dest[index++] = Y - 0.34413 * (U - 128) - 0.71414 * (V - 128); //G
  16.             Dest[index++] = Y + 1.772 * (U - 128); //B
  17.         }
  18.     }
  19. }

实际转换效果如下图，太亮或者边界会出现失真，效果不理想，原因是G分量有可能出现负值，并没有考虑到边界问题，这是网上方法普遍存在问题。

方法二：

为了解决上述边界会造成失真问题，建议采用方法二改为查表方式，可以防止出现边界失真问题，参考了国外一大神的方法，链接如下：http://iyenn.com/index/link?url=http://wss.co.uk/pinknoise/yuv2rgb/

实现代码如下：

 

  1. static int Table_fv1[256] = { -180, -179, -177, -176, -174, -173, -172, -170, -169, -167, -166, -165, -163, -162, -160, -159, -158, -156, -155, -153, -152, -151, -149, -148, -146, -145, -144, -142, -141, -139, -138, -137,  -135, -134, -132, -131, -130, -128, -127, -125, -124, -123, -121, -120, -118, -117, -115, -114, -113, -111, -110, -108, -107, -106, -104, -103, -101, -100, -99, -97, -96, -94, -93, -92, -90,  -89, -87, -86, -85, -83, -82, -80, -79, -78, -76, -75, -73, -72, -71, -69, -68, -66, -65, -64,-62, -61, -59, -58, -57, -55, -54, -52, -51, -50, -48, -47, -45, -44, -43, -41, -40, -38, -37,  -36, -34, -33, -31, -30, -29, -27, -26, -24, -23, -22, -20, -19, -17, -16, -15, -13, -12, -10, -9, -8, -6, -5, -3, -2, 0, 1, 2, 4, 5, 7, 8, 9, 11, 12, 14, 15, 16, 18, 19, 21, 22, 23, 25, 26, 28, 29, 30, 32, 33, 35, 36, 37, 39, 40, 42, 43, 44, 46, 47, 49, 50, 51, 53, 54, 56, 57, 58, 60, 61, 63, 64, 65, 67, 68, 70, 71, 72, 74, 75, 77, 78, 79, 81, 82, 84, 85, 86, 88, 89, 91, 92, 93, 95, 96, 98, 99, 100, 102, 103, 105, 106, 107, 109, 110, 112, 113, 114, 116, 117, 119, 120, 122, 123, 124, 126, 127, 129, 130, 131, 133, 134, 136, 137, 138, 140, 141, 143, 144, 145, 147, 148,  150, 151, 152, 154, 155, 157, 158, 159, 161, 162, 164, 165, 166, 168, 169, 171, 172, 173, 175, 176, 178 };
  2. static int Table_fv2[256] = { -92, -91, -91, -90, -89, -88, -88, -87, -86, -86, -85, -84, -83, -83, -82, -81, -81, -80, -79, -78, -78, -77, -76, -76, -75, -74, -73, -73, -72, -71, -71, -70, -69, -68, -68, -67, -66, -66, -65, -64, -63, -63, -62, -61, -61, -60, -59, -58, -58, -57, -56, -56, -55, -54, -53, -53, -52, -51, -51, -50, -49, -48, -48, -47, -46, -46, -45, -44, -43, -43, -42, -41, -41, -40, -39, -38, -38, -37, -36, -36, -35, -34, -33, -33, -32, -31, -31, -30, -29, -28, -28, -27, -26, -26, -25, -24, -23, -23, -22, -21, -21, -20, -19, -18, -18, -17, -16, -16, -15, -14, -13, -13, -12, -11, -11, -10, -9, -8, -8, -7, -6, -6, -5, -4, -3, -3, -2, -1, 0, 0, 1, 2, 2, 3, 4, 5, 5, 6, 7, 7, 8, 9, 10, 10, 11, 12, 12, 13, 14, 15, 15, 16, 17, 17, 18, 19, 20, 20, 21, 22, 22, 23, 24, 25, 25, 26, 27, 27, 28, 29, 30, 30, 31, 32, 32, 33, 34, 35, 35, 36, 37, 37, 38, 39, 40, 40, 41, 42, 42, 43, 44, 45, 45, 46, 47, 47, 48, 49, 50, 50, 51, 52, 52, 53, 54, 55, 55, 56, 57, 57, 58, 59, 60, 60, 61, 62, 62, 63, 64, 65, 65, 66, 67, 67, 68, 69, 70, 70, 71, 72, 72, 73, 74, 75, 75, 76, 77, 77, 78, 79, 80, 80, 81, 82, 82, 83, 84, 85, 85, 86, 87, 87, 88, 89, 90, 90 };
  3. static int Table_fu1[256] = { -44, -44, -44, -43, -43, -43, -42, -42, -42, -41, -41, -41, -40, -40, -40, -39, -39, -39, -38, -38, -38, -37, -37, -37, -36, -36, -36, -35, -35, -35, -34, -34, -33, -33, -33, -32, -32, -32, -31, -31, -31, -30, -30, -30, -29, -29, -29, -28, -28, -28, -27, -27, -27, -26, -26, -26, -25, -25, -25, -24, -24, -24, -23, -23, -22, -22, -22, -21, -21, -21, -20, -20, -20, -19, -19, -19, -18, -18, -18, -17, -17, -17, -16, -16, -16, -15, -15, -15, -14, -14, -14, -13, -13, -13, -12, -12, -11, -11, -11, -10, -10, -10, -9, -9, -9, -8, -8, -8, -7, -7, -7, -6, -6, -6, -5, -5, -5, -4, -4, -4, -3, -3, -3, -2, -2, -2, -1, -1, 0, 0, 0, 1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 5, 5, 6, 6, 6, 7, 7, 7, 8, 8, 8, 9, 9, 9, 10, 10, 11, 11, 11, 12, 12, 12, 13, 13, 13, 14, 14, 14, 15, 15, 15, 16, 16, 16, 17, 17, 17, 18, 18, 18, 19, 19, 19, 20, 20, 20, 21, 21, 22, 22, 22, 23, 23, 23, 24, 24, 24, 25, 25, 25, 26, 26, 26, 27, 27, 27, 28, 28, 28, 29, 29, 29, 30, 30, 30, 31, 31, 31, 32, 32, 33, 33, 33, 34, 34, 34, 35, 35, 35, 36, 36, 36, 37, 37, 37, 38, 38, 38, 39, 39, 39, 40, 40, 40, 41, 41, 41, 42, 42, 42, 43, 43 };
  4. static int Table_fu2[256] = { -227, -226, -224, -222, -220, -219, -217, -215, -213, -212, -210, -208, -206, -204, -203, -201, -199, -197, -196, -194, -192, -190, -188, -187, -185, -183, -181, -180, -178, -176, -174, -173, -171, -169, -167, -165, -164, -162, -160, -158, -157, -155, -153, -151, -149, -148, -146, -144, -142, -141, -139, -137, -135, -134, -132, -130, -128, -126, -125, -123, -121, -119, -118, -116, -114, -112, -110, -109, -107, -105, -103, -102, -100, -98, -96, -94, -93, -91, -89, -87, -86, -84, -82, -80, -79, -77, -75, -73, -71, -70, -68, -66, -64, -63, -61, -59, -57, -55, -54, -52, -50, -48, -47, -45, -43, -41, -40, -38, -36, -34, -32, -31, -29, -27, -25, -24, -22, -20, -18, -16, -15, -13, -11, -9, -8, -6, -4, -2, 0, 1, 3, 5, 7, 8, 10, 12, 14, 15, 17, 19, 21, 23, 24, 26, 28, 30, 31, 33, 35, 37, 39, 40, 42, 44, 46, 47, 49, 51, 53, 54, 56, 58, 60, 62, 63, 65, 67, 69, 70, 72, 74, 76, 78, 79, 81, 83, 85, 86, 88, 90, 92, 93, 95, 97, 99, 101, 102, 104, 106, 108, 109, 111, 113, 115, 117, 118, 120, 122, 124, 125, 127, 129, 131, 133, 134, 136, 138, 140, 141, 143, 145, 147, 148, 150, 152, 154, 156, 157, 159, 161, 163, 164, 166, 168, 170, 172, 173, 175, 177, 179, 180, 182, 184, 186, 187, 189, 191, 193, 195, 196, 198, 200, 202, 203, 205, 207, 209, 211, 212, 214, 216, 218, 219, 221, 223, 225 };
  5.  
  6. void ConvertYUV420SPToBGR(unsigned char* src,unsigned char* Dst,int ImageWidth,int ImageHeight)
  7. {
  8.     if (ImageWidth < 1 || ImageHeight < 1 || src == NULL || Dst == NULL)
  9.         return ;
  10.     const long len = ImageWidth * ImageHeight;
  11.     unsigned char* yData = src;
  12.     unsigned char* vData = &yData[len];
  13.     unsigned char* uData = &vData[len >> 2];
  15.     int bgr[3];
  16.     int yIdx,uIdx,vIdx,idx;
  17.     int rdif,invgdif,bdif;
  18.     for (int i = 0;i < ImageHeight;i++){
  19.         for (int j = 0;j < ImageWidth;j++){
  20.             yIdx = i * ImageWidth + j;
  21.             vIdx = (i/2) * (ImageWidth/2) + (j/2);
  22.             uIdx = vIdx;
  23.  
  24.             rdif = Table_fv1[vData[vIdx]];
  25.             invgdif = Table_fu1[uData[uIdx]] + Table_fv2[vData[vIdx]];
  26.             bdif = Table_fu2[uData[uIdx]];
  27.  
  28.             bgr[0] = yData[yIdx] + bdif;    
  29.             bgr[1] = yData[yIdx] - invgdif;
  30.             bgr[2] = yData[yIdx] + rdif;
  31.  
  32.             for (int k = 0;k < 3;k++){
  33.                 idx = (i * ImageWidth + j) * 3 + k;
  34.                 if(bgr[k] >= 0 && bgr[k] <= 255)
  35.                     Dst[idx] = bgr[k];
  36.                 else
  37.                     Dst[idx] = (bgr[k] < 0)?0:255;
  38.             }
  39.         }
  40.     }
  41. }

实际转换效果如下： 

上述效果较好。

方法三：

近期在看opencv，发现了可以使用cv::saturate_cast<>()防止数据溢出，关于cv::saturate_cast<>()的介绍有兴趣的读者可以了解下：

http://iyenn.com/rec/327362.html

这种方法应该也可以，由于距离方法一和二过去很久，实验环境已经拆除，数据没有保存，无法拿到当初的数据，并没有亲自做实验，应该也是可以解决，更新此方法的代码防止时间长遗忘掉，做备份后面有时间再做实验

  1. void ConvertYUV420SPToRGB(unsigned char *Src, unsigned char *Dest, int ImageWidth, int ImageHeight)
  2. {
  3. 	int total = ImageWidth * ImageHeight;
  4. 	unsigned char *ybase = Src;
  5. 	unsigned char *ubase = &Src[total];
  6. 	unsigned int index = 0;
  7. 	for (int y = 0; y < ImageHeight; y++) {
  8. 		for (int x = 0; x < ImageWidth; x++) {
  9. 			//YYYYYYYYVUVU
  10. 			u_char Y = ybase[x + y * ImageWidth];
  11. 			u_char U = ubase[y / 2 * ImageWidth + (x / 2) * 2 + 1];
  12. 			u_char V = ubase[y / 2 * ImageWidth + (x / 2) * 2];
  13.  
  14. 			Dest[index++] = cv::saturate_cast(Y + 1.402* (V - 128)); //R
  15. 			Dest[index++] = cv::saturate_cast(Y - 0.34413 * (U - 128) - 0.71414 * (V - 128)); //G
  16. 			Dest[index++] = cv::saturate_cast(Y + 1.772 * (U - 128)); //B
  17. 		}
  18. 	}
  19. }

 

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注：本文转载自blog.csdn.net的Huo的藏经阁的文章"https://blog.csdn.net/weixin_42730667/article/details/97233856"。版权归原作者所有，此博客不拥有其著作权，亦不承担相应法律责任。如有侵权，请联系我们删除。
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