nv21(yuv420sp)左右镜像翻转实现

谁践踏了优雅 2022-12-15 03:36 328阅读 0赞

yuv格式说明参考：[图解YU12、I420、YV12、NV12、NV21、YUV420P、YUV420SP、YUV422P、YUV444P的区别][YU12_I420_YV12_NV12_NV21_YUV420P_YUV420SP_YUV422P_YUV444P]

输入数据是yuv，输出是flipyuv, uv分量是交替存储，uvsize刚好是height/2 \* width, 下面的实现没有考虑stride的情况。

void CvtNV21FlipH(Mat& mYUV, Mat& mflipYUV) {
        int width = mYUV.cols;
        int height = mYUV.rows;
    
        // flip Y data
        for (int j = 0; j < height; j++) {
            uint8_t* ydata = mYUV.data + (j+1)*width;
            uint8_t* flipYdata = mflipYUV.data + j*width;
            for (int i = 0; i < width; i++) {
                int idx = width - 1 - i;
                flipYdata[i] = ydata[idx];
            }
        }
    
        //flip VU data
        int yLen = width * height;
        for (int j = 0; j < height/2; j++) {
            uint8_t* vu = mYUV.data + yLen + (j+1)*width;
            uint8_t* flipVU = mflipYUV.data + yLen + j*width;
            for (int i = 0; i < width; i+=2) {
                int idx = width - 2 - i;
                flipVU[i] = vu[idx];
                flipVU[i+1] = vu[idx+1];
            }
        }
    }

下面的实现加上stride参数

因为是nv21, yvu420sp格式，vstride实际上是vu数据一行的宽度(width + stride), ystride就是Y分量一行的宽度(width + stride)

ystride = width + stride  
vstride = width + stride;

输入参数h,w是输入图像的实际宽和高，矩阵的rows = h+h/2, cols = ystride，ystride大于等于w.

void CvtNV21FlipH(Mat& mYUV, int h, int w, int ystride, int ustride, int vstride, Mat& mflipYUV) {
        int width = mYUV.cols;
        int height = mYUV.rows;
    
        // flip Y data
        for (int j = 0; j < h; j++) {
            uint8_t* ydata = mYUV.data + (j+1)*ystride;
            uint8_t* flipYdata = mflipYUV.data + j*ystride;
            for (int i = 0; i < w; i++) {
                int idx = w - 1 - i;
                flipYdata[i] = ydata[idx];
            }
        }
         //flip VU data
        int yLen = ystride * h;
        for (int j = 0; j < h/2; j++) {
            uint8_t* vu = mYUV.data + yLen + (j+1)*vstride;
            uint8_t* flipvu = mflipYUV.data + yLen + j*vstride;
            for (int i = 0; i < w; i+=2) {
                int idx = w - 2 - i;
                flipvu[i] = vu[idx];
                flipvu[i+1] = vu[idx+1];
            }
        }
    }

[YU12_I420_YV12_NV12_NV21_YUV420P_YUV420SP_YUV422P_YUV444P]: https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2Fbyhook%2Fffmpeg4android%2Fblob%2Fmaster%2Freadme%2F%25E5%259B%25BE%25E8%25A7%25A3YU12%25E3%2580%2581I420%25E3%2580%2581YV12%25E3%2580%2581NV12%25E3%2580%2581NV21%25E3%2580%2581YUV420P%25E3%2580%2581YUV420SP%25E3%2580%2581YUV422P%25E3%2580%2581YUV444P%25E7%259A%2584%25E5%258C%25BA%25E5%2588%25AB.md