YUV格式学习：I420(YUV420P)、YV12、NV12、NV21格式转换成RGB24

对于YUV420的格式，网上有一大堆资料，这里就不说了。直奔主题，给出如何转换的函数，一如既往，只用代码说事。

YUV420有打包格式(Packed)，一如前文所述。同时还有平面格式(Planar)，即Y、U、V是分开存储的，每个分量占一块地方，其中Y为width*height，而U、V合占Y的一半，该种格式每个像素占12比特。根据U、V的顺序，分出2种格式，U前V后即YUV420P，也叫I420，V前U后，叫YV12(YV表示Y后面跟着V，12表示12bit)。另外，还有一种半平面格式(Semi-planar)，即Y单独占一块地方，但其后U、V又紧挨着排在一起，根据U、V的顺序，又有2种，U前V后叫NV12，在国内好像很多人叫它为YUV420SP格式；V前U后叫NV21。这种格式似乎比NV16稍受欢迎。

首先给出转换查询表的生成函数，代码是在网上找来的，如下：

static long int crv_tab[256];   
static long int cbu_tab[256];   
static long int cgu_tab[256];   
static long int cgv_tab[256];   
static long int tab_76309[256]; 
static unsigned char clp[1024];   //for clip in CCIR601   
 
void init_yuv420p_table() 
{   
    long int crv,cbu,cgu,cgv;   
    int i,ind;      
    static int init = 0;
 
    if (init == 1) return;
 
    crv = 104597; cbu = 132201;  /* fra matrise i global.h */   
    cgu = 25675;  cgv = 53279;   
   
    for (i = 0; i < 256; i++)    
    {   
        crv_tab[i] = (i-128) * crv;   
        cbu_tab[i] = (i-128) * cbu;   
        cgu_tab[i] = (i-128) * cgu;   
        cgv_tab[i] = (i-128) * cgv;   
        tab_76309[i] = 76309*(i-16);   
    }   
   
    for (i = 0; i < 384; i++)   
        clp[i] = 0;   
    ind = 384;   
    for (i = 0;i < 256; i++)   
        clp[ind++] = i;   
    ind = 640;   
    for (i = 0;i < 384; i++)   
        clp[ind++] = 255;
 
    init = 1;
}

下面给出YUV420平面格式的转换函数，如下：

/**
内存分布
                    w
            +--------------------+
            |Y0Y1Y2Y3...         |
            |...                 |   h
            |...                 |
            |                    |
            +--------------------+
            |U0U1      |
            |...       |   h/2
            |...       |
            |          |
            +----------+
            |V0V1      |
            |...       |  h/2
            |...       |
            |          |
            +----------+
                w/2
 */
void yuv420p_to_rgb24(YUV_TYPE type, unsigned char* yuvbuffer,unsigned char* rgbbuffer, int width,int height)   
{
    int y1, y2, u, v;    
    unsigned char *py1, *py2;   
    int i, j, c1, c2, c3, c4;   
    unsigned char *d1, *d2;   
    unsigned char *src_u, *src_v;
    static int init_yuv420p = 0;
    
    src_u = yuvbuffer + width * height;   // u
    src_v = src_u + width * height / 4;  //  v
 
    if (type == FMT_YV12)	//默认I420
    {
        src_v = yuvbuffer + width * height;   // v
        src_u = src_u + width * height / 4;  //  u
    }
    py1 = yuvbuffer;   // y
    py2 = py1 + width;   
    d1 = rgbbuffer;   
    d2 = d1 + 3 * width;   
 
    init_yuv420p_table();
 
    for (j = 0; j < height; j += 2)    
    {    
        for (i = 0; i < width; i += 2)    
        {
            u = *src_u++;   
            v = *src_v++;   
   
            c1 = crv_tab[v];   
            c2 = cgu_tab[u];   
            c3 = cgv_tab[v];   
            c4 = cbu_tab[u];   
   
            //up-left   
            y1 = tab_76309[*py1++];    
            *d1++ = clp[384+((y1 + c1)>>16)];     
            *d1++ = clp[384+((y1 - c2 - c3)>>16)];   
            *d1++ = clp[384+((y1 + c4)>>16)];   
   
            //down-left   
            y2 = tab_76309[*py2++];   
            *d2++ = clp[384+((y2 + c1)>>16)];     
            *d2++ = clp[384+((y2 - c2 - c3)>>16)];   
            *d2++ = clp[384+((y2 + c4)>>16)];   
   
            //up-right   
            y1 = tab_76309[*py1++];   
            *d1++ = clp[384+((y1 + c1)>>16)];     
            *d1++ = clp[384+((y1 - c2 - c3)>>16)];   
            *d1++ = clp[384+((y1 + c4)>>16)];   
   
            //down-right   
            y2 = tab_76309[*py2++];   
            *d2++ = clp[384+((y2 + c1)>>16)];     
            *d2++ = clp[384+((y2 - c2 - c3)>>16)];   
            *d2++ = clp[384+((y2 + c4)>>16)];   
        }
        d1  += 3*width;
        d2  += 3*width;
        py1 += width;
        py2 += width;
    }
}

再给出YUV420SP转换的函数，如下：

void yuv420sp_to_rgb24(YUV_TYPE type, unsigned char* yuvbuffer,unsigned char* rgbbuffer, int width,int height)   
{
    int y1, y2, u, v;    
    unsigned char *py1, *py2;   
    int i, j, c1, c2, c3, c4;   
    unsigned char *d1, *d2;   
    unsigned char *src_u;
    static int init_yuv420p = 0;
 
    src_u = yuvbuffer + width * height;   // u
 
    py1 = yuvbuffer;   // y
    py2 = py1 + width;   
    d1 = rgbbuffer;   
    d2 = d1 + 3 * width;   
 
    init_yuv420p_table();
 
    for (j = 0; j < height; j += 2)    
    {    
        for (i = 0; i < width; i += 2)    
        {
            if (type ==  FMT_NV12)
            {
                u = *src_u++;   
                v = *src_u++;      // v紧跟u，在u的下一个位置
            }
            if (type == FMT_NV21)
            {
                v = *src_u++;   
                u = *src_u++;      // u紧跟v，在v的下一个位置
            }
 
            c1 = crv_tab[v];   
            c2 = cgu_tab[u];   
            c3 = cgv_tab[v];   
            c4 = cbu_tab[u];   
 
            //up-left   
            y1 = tab_76309[*py1++];    
            *d1++ = clp[384+((y1 + c1)>>16)];     
            *d1++ = clp[384+((y1 - c2 - c3)>>16)];   
            *d1++ = clp[384+((y1 + c4)>>16)];   
 
            //down-left   
            y2 = tab_76309[*py2++];   
            *d2++ = clp[384+((y2 + c1)>>16)];     
            *d2++ = clp[384+((y2 - c2 - c3)>>16)];   
            *d2++ = clp[384+((y2 + c4)>>16)];   
 
            //up-right   
            y1 = tab_76309[*py1++];   
            *d1++ = clp[384+((y1 + c1)>>16)];     
            *d1++ = clp[384+((y1 - c2 - c3)>>16)];   
            *d1++ = clp[384+((y1 + c4)>>16)];   
 
            //down-right   
            y2 = tab_76309[*py2++];   
            *d2++ = clp[384+((y2 + c1)>>16)];     
            *d2++ = clp[384+((y2 - c2 - c3)>>16)];   
            *d2++ = clp[384+((y2 + c4)>>16)];   
        }
        d1  += 3*width;
        d2  += 3*width;
        py1 += width;
        py2 += width;
    }
}

YUV_TYPE类型可自定义

typedef enum
{
FMT_YUYV=1, FMT_YVYU, FMT_UYVY, FMT_VYUY, FMT_YV12, FMT_NV12, FMT_NV21, FMT_I420
}YUV_TYPE;