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将BGR转换成为YUV420SP图像格式

//BGR2YUV(YUV420SP_NV21)
void enCodeYUV420SP(unsigned  char* yuv420sp, unsigned char* rgb, int width, int height)
{
    if (yuv420sp == NULL || rgb == NULL)
        return;
    int frameSize = width*height;
    int yIndex = 0;
    int uvIndex = frameSize;
  
    int R, G, B, Y, U, V;
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            B = rgb[(i * width + j) * 3 + 0];
            G = rgb[(i * width + j) * 3 + 1];
            R = rgb[(i * width + j) * 3 + 2];
  
            //RGB to YUV
            Y = ((66 * R + 129 * G + 25 * B + 128) >> 8) + 16;
            U = ((-38 * R - 74 * G + 112 * B + 128) >> 8) + 128;
            V = ((112 * R - 94 * G - 18 * B + 128) >> 8) + 128;
  
            yuv420sp[yIndex++] = (unsigned char)((Y < 0) ? 0 : ((Y > 255) ? 255 : Y));
            if (i % 2 == 0 && j % 2 == 0)
            {
                yuv420sp[uvIndex++] = (unsigned char)((V < 0) ? 0 : ((V > 255) ? 255 : V));//UV交替排列
                yuv420sp[uvIndex++] = (unsigned char)((U < 0) ? 0 : ((U > 255) ? 255 : U));
            }
        }
    }
}

cv::Mat img = cv::imread(imgPath);
         
  
        int height = img.rows;
        int width = img.cols;
      
        unsigned char* img_bgr_data = (unsigned char*)malloc(height*width * 3 * sizeof(unsigned char));
        for (int i = 0; i < height; i++)
        {
            unsigned char* current_row = img.ptr<uchar>(i);
            for (int j = 0; j < width; j++)
            {
                img_bgr_data[(i * width + j) * 3 + 0] = current_row[j * 3 + 0];//B
                img_bgr_data[(i * width + j) * 3 + 1] = current_row[j * 3 + 1];//G
                img_bgr_data[(i * width + j) * 3 + 2] = current_row[j * 3 + 2];//R
            }
        }
      
        //RGB->NV21(YUV420SP)
        unsigned char* img_nv21_data = (unsigned char*)malloc(height*width * 3 / 2 * sizeof(unsigned char));
         
         
 
         
        enCodeYUV420SP(img_nv21_data, img_bgr_data, width, height);
//Mat img_BGR(height, width, CV_8UC3);
        //cvtColor(img_nv21, img_BGR, CV_YUV2BGR_NV21);//YUV420sp->BGR
        //cv::cvtColor(img_nv21, img_BGR, cv::COLOR_YUV420sp2BGR);
        //cv::imwrite("./img_BGR.jpg", img_BGR);        