OpenCV on a sheet of paper there is a rectangle with a dot inside, need to convert the image to a matrix view?

Question

OpenCV

OpenCV on a sheet of paper has a rectangle with a dot inside, you need to convert the image to a matrix view.
So that the elements of the matrix are zeros and ones. The units are the outline of the rectangle and the point.
The bottom line is that I need to link the distance from the edge of the sheet to the rectangle and the number of pixels from the edge of the sheet to the rectangle.