论YUV422(YUYV)与YUV420相互转换

Example 2.13. V4L2_PIX_FMT_YUYV 4 × 4 pixelimage

start + 0:	Y'00	Cb00	Y'01	Cr00	Y'02	Cb01	Y'03	Cr01
start + 8:	Y'10	Cb10	Y'11	Cr10	Y'12	Cb11	Y'13	Cr11
start + 16:	Y'20	Cb20	Y'21	Cr20	Y'22	Cb21	Y'23	Cr21
start + 24:	Y'30	Cb30	Y'31	Cr30	Y'32	Cb31	Y'33	Cr31

YUV422码流存放位置

(转自http://www.chineselinuxuniversity.net/kerneldocs/media/V4L2-PIX-FMT-YUYV.html)

Example 2.18. V4L2_PIX_FMT_YUV420 4 × 4 pixelimage

start + 0:	Y'00	Y'01	Y'02	Y'03
start + 4:	Y'10	Y'11	Y'12	Y'13
start + 8:	Y'20	Y'21	Y'22	Y'23
start + 12:	Y'30	Y'31	Y'32	Y'33
start + 16:	Cb00	Cb01
start + 18:	Cb10	Cb11
start + 20:	Cr00	Cr01
start + 22:	Cr10	Cr11

YUV420码流存放位置

(转自http://www.chineselinuxuniversity.net/kerneldocs/media/re18.html该处是YVU420)

这里要顺带提一下YUV444,既无损YUV色彩空间.一个Y带一个Cb一个Cr,即YCbCr.

YUV422采样即从YUV444基础上,从第一个Y开始只保留Cb,剔去Cr,第二个Y只保留Cr剔去Cb…...这样交替采样,长度大小为width*height*2,Y:U:V=4:2:2,一个色彩分量占一个字节.

而YUV420即从YUV422基础上进行隔行采样,例如第一行只保留Cb,第二行只保留Cr……这样交替进行,Y:U:V=4:2:0并不是没有V分量,也可以是Y:U:V=4:0:2.相信这样大家容易理解.最后在这个基础上,把Y,U,V三种分量打包排列,即如上图,长度大小为width*height*3/2.

说了这么多,是时候贴上具体代码.

<span style="font-size:14px;">#include <stdio.h>
#include <string.h>


#define     READ_WRITE_FILE_SIZE    176*144*2  //YUV422 图像分辨率为177x144

unsigned char filebuf[38017] = {0};

int YUV422To420(unsigned char yuv422[], unsigned char yuv420[], int width, int height)
{

       int ynum=width*height;
       int i,j,k=0;
    //得到Y分量
       for(i=0;i<ynum;i++){
           yuv420[i]=yuv422[i*2];
       }
    //得到U分量
       for(i=0;i<height;i++){
           if((i%2)!=0)continue;
           for(j=0;j<(width/2);j++){
               if((4*j+1)>(2*width))break;
               yuv420[ynum+k*2*width/4+j]=yuv422[i*2*width+4*j+1];
                       }
            k++;
       }
       k=0;
    //得到V分量
       for(i=0;i<height;i++){
           if((i%2)==0)continue;
           for(j=0;j<(width/2);j++){
               if((4*j+3)>(2*width))break;
               yuv420[ynum+ynum/4+k*2*width/4+j]=yuv422[i*2*width+4*j+3];

           }
            k++;
       }


       return 1;
}

int main(void)
{
    int len = 0;
    FILE *fpr, *fpw;
    unsigned char buf[READ_WRITE_FILE_SIZE];
    fpr = fopen( "WEBCAM-00012.YUV", "rb" );
    fpw = fopen( "yuyv_2_yy_u_v.yuv", "wb" );
    if( fpr == NULL || fpw == NULL )
    {
        printf("can not read or write file
");
        fcloseall();
        return 1;
    }
    fread( buf, READ_WRITE_FILE_SIZE, 1, fpr );
    if(YUV422To420(buf,filebuf,176,144))printf("ok
");
    printf("size:%d",sizeof(filebuf));
    fwrite( &filebuf, sizeof(filebuf), 1, fpw );
    fcloseall();
    return 0;
}
</span>

<span style="font-size:14px;">#include <stdio.h>
#include <string.h>


#define     READ_WRITE_FILE_SIZE    176*144*2  //YUV422 图像分辨率为177x144

unsigned char filebuf[38017] = {0};

int YUV422To420(unsigned char yuv422[], unsigned char yuv420[], int width, int height)
{

       int ynum=width*height;
       int i,j,k=0;
    //得到Y分量
       for(i=0;i<ynum;i++){
           yuv420[i]=yuv422[i*2];
       }
    //得到U分量
       for(i=0;i<height;i++){
           if((i%2)!=0)continue;
           for(j=0;j<(width/2);j++){
               if((4*j+1)>(2*width))break;
               yuv420[ynum+k*2*width/4+j]=yuv422[i*2*width+4*j+1];
                       }
            k++;
       }
       k=0;
    //得到V分量
       for(i=0;i<height;i++){
           if((i%2)==0)continue;
           for(j=0;j<(width/2);j++){
               if((4*j+3)>(2*width))break;
               yuv420[ynum+ynum/4+k*2*width/4+j]=yuv422[i*2*width+4*j+3];

           }
            k++;
       }


       return 1;
}

int main(void)
{
    int len = 0;
    FILE *fpr, *fpw;
    unsigned char buf[READ_WRITE_FILE_SIZE];
    fpr = fopen( "WEBCAM-00012.YUV", "rb" );
    fpw = fopen( "yuyv_2_yy_u_v.yuv", "wb" );
    if( fpr == NULL || fpw == NULL )
    {
        printf("can not read or write file
");
        fcloseall();
        return 1;
    }
    fread( buf, READ_WRITE_FILE_SIZE, 1, fpr );
    if(YUV422To420(buf,filebuf,176,144))printf("ok
");
    printf("size:%d",sizeof(filebuf));
    fwrite( &filebuf, sizeof(filebuf), 1, fpw );
    fcloseall();
    return 0;
}