NV12格式转RGB的CUDA实现

 NV12格式是yuv420格式的一种，NV12格式的u,v排布顺序为交错排布，假如一幅图像尺寸为W*H，则先Y分量有W*H个，然后U分量和V分量交错排布，U分量和V分量各有W*H/4个，U，V加起来总数是Y分量的一半。

NV12内存YUV分量排布如下所示：

 下面是CUDA实现的NV12格式到BGR格式的转换代码。StepY,StepUV分别为ffmpeg解码出的源数据中的Y分量一行的宽度和UV分量一行的宽度，比实际的图像宽度要大。

__global__ void YCrCb2RGBConver(uchar *pYdata, uchar *pUVdata,int stepY, int stepUV, uchar *pImgData, int width, int height, int channels)
{
    const int tidx = blockIdx.x * blockDim.x + threadIdx.x;
    const int tidy = blockIdx.y * blockDim.y + threadIdx.y;

    if (tidx < width && tidy < height)
    {
        int indexY, indexU, indexV;
        uchar Y, U, V;
        indexY = tidy * stepY + tidx;    
        Y = pYdata[indexY];

        if (tidx % 2 == 0)
        {
            indexU = tidy / 2 * stepUV + tidx;
            indexV = tidy / 2 * stepUV + tidx + 1;
            U = pUVdata[indexU];
            V = pUVdata[indexV];
        }
        else if (tidx % 2 == 1)
        {
            indexV = tidy / 2 * stepUV + tidx;
            indexU = tidy / 2 * stepUV + tidx - 1;
            U = pUVdata[indexU];
            V = pUVdata[indexV];
        }

        pImgData[(tidy*width + tidx) * channels + 2] = uchar (Y + 1.402 * (V - 128));
        pImgData[(tidy*width + tidx) * channels + 1] = uchar (Y - 0.34413 * (U - 128) - 0.71414*(V - 128));
        pImgData[(tidy*width + tidx) * channels + 0] = uchar (Y + 1.772*(U - 128));
    }
}

CPU版本如下：

void YCrCb2RGBConver(uchar *pYdata, uchar *pUVdata, int stepY, int stepUV, uchar *pImgData, int width, int height, int channels)
{

    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            int indexY, indexU, indexV;
            uchar Y, U, V;
            indexY = i * stepY + j;
            Y = pYdata[indexY];

            if (j % 2 == 0)
            {
                indexU = i / 2 * stepUV + j;
                indexV = i / 2 * stepUV + j + 1;
                U = pUVdata[indexU];
                V = pUVdata[indexV];
            }
            else if (j % 2 == 1)
            {
                indexV = i / 2 * stepUV + j;
                indexU = i / 2 * stepUV + j - 1;
                U = pUVdata[indexU];
                V = pUVdata[indexV];
            }

            pImgData[(i*width + j) * channels + 2] = uchar(Y + 1.402 * (V - 128));
            pImgData[(i*width + j) * channels + 1] = uchar(Y - 0.34413 * (U - 128) - 0.71414*(V - 128));
            pImgData[(i*width + j) * channels + 0] = uchar(Y + 1.772*(U - 128));
        }
    }
}