C# OpenCvSharp：图像加减超出0-255需要模运算

比如

Mat img = Cv2.ImRead(@"01.png");
img = img - new Scalar(255, 255, 255);

运算结果得到全黑，但我希望它的颜色翻转

Mat img1 = Cv2.ImRead(@"01.png");
Mat img2 = Cv2.ImRead(@"02.png");
Mat test = img2 - img1 + img1;

结果和img2不一样

怎么能让它进行模运算？

自答，用for循环写了个解决方案，不过速度比原来的要慢

for (int k = 0; k < 3; k++)
{
    for (int i = 0; i < img1.Height; ++i)
    {
        for (int j = 0; j < img1.Width; ++j)
        {
            diff.At<Vec3b>(i, j)[k] = (byte)((img2.At<Vec3b>(i, j)[k] - img1.At<Vec3b>(i, j)[k]) % 256);
        }
    }
}

for (int k = 0; k < 3; k++)
{
    for (int i = 0; i < img1.Height; ++i)
    {
        for (int j = 0; j < img1.Width; ++j)
        {
            add.At<Vec3b>(i, j)[k] = (byte)((diff.At<Vec3b>(i, j)[k] + img1.At<Vec3b>(i, j)[k]) % 256);
        }
    }
}

numpy的是模运算，你把这两个转换成numpy的类型，然后再加，就是模运算了

img