Optimize - draw gradient function

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Hi,

Performance analysis shows me that below function is the slowest function in my program. Is it possible to optimize performance of this gradient function? (i.e. by some matrix operation)

void gradient(cv::Mat& image, cv::Scalar c1, cv::Scalar c2)
{
    auto alphaStep = 1.0 / image.rows;
    auto alpha = 0.0;
    for (int y = 0; y < image.rows; y++) {
        cv::Vec4b* rowImage = image.ptr<cv::Vec4b>(y);
        cv::Scalar color(c1(0)*(1 - alpha) + c2(0)*(alpha), c1(1)*(1 - alpha) + c2(1)*(alpha), c1(2)*(1 - alpha) + c2(2)*(alpha), 255);
        for (int x = 0; x < image.cols; x++) {
            rowImage[x][0] = color[0];
            rowImage[x][1] = color[1];
            rowImage[x][2] = color[2];
            rowImage[x][3] = color[3];
        }
        alpha += alphaStep;
    }
}