例图
Mat src = imread("1.jpg");
Mat bgra;
cvtColor(src, bgra, COLOR_BGR2BGRA);
for (size_t i = 0; i < src.rows; i++)
{
for (size_t j = 0; j < src.cols; j++)
{
if (src.at<Vec3b>(i, j)[0] > 127)
{
bgra.at<Vec4b>(i,j)[3] = 0;
}
}
}
imwrite("x.png", bgra);
结果图