CODE EXAMPLE FOR PYTHON

remove watermark using python

Mat im = [load the color image here];

Mat gr, bg, bw, dark;

cvtColor(im, gr, CV_BGR2GRAY);

// approximate the background
bg = gr.clone();
for (int r = 1; r < 5; r++)
{
    Mat kernel2 = getStructuringElement(MORPH_ELLIPSE, Size(2*r+1, 2*r+1));
    morphologyEx(bg, bg, CV_MOP_CLOSE, kernel2);
    morphologyEx(bg, bg, CV_MOP_OPEN, kernel2);
}

// difference = background - initial
Mat dif = bg - gr;
// threshold the difference image so we get dark letters
threshold(dif, bw, 0, 255, CV_THRESH_BINARY_INV | CV_THRESH_OTSU);
// threshold the background image so we get dark region
threshold(bg, dark, 0, 255, CV_THRESH_BINARY_INV | CV_THRESH_OTSU);

// extract pixels in the dark region
vector<unsigned char> darkpix(countNonZero(dark));
int index = 0;
for (int r = 0; r < dark.rows; r++)
{
    for (int c = 0; c < dark.cols; c++)
    {
        if (dark.at<unsigned char>(r, c))
        {
            darkpix[index++] = gr.at<unsigned char>(r, c);
        }
    }
}
// threshold the dark region so we get the darker pixels inside it
threshold(darkpix, darkpix, 0, 255, CV_THRESH_BINARY | CV_THRESH_OTSU);

// paste the extracted darker pixels
index = 0;
for (int r = 0; r < dark.rows; r++)
{
    for (int c = 0; c < dark.cols; c++)
    {
        if (dark.at<unsigned char>(r, c))
        {
            bw.at<unsigned char>(r, c) = darkpix[index++];
        }
    }
}