OpenCV - Scan an image with a rectangle

Question

I would like to scan my picture with a rectangle (openCV and python). This rectangle has to go all over the image.

I proceed like this but it doesn't work at all. My rectangle has a size of 20

for i in range(0,height):
     for j in range(0,width):
          pt1=(0+i,0+j)
          pt2=(20+i,20+j)
          point.append([pt1,pt2])
          cv2.rectangle(res,pt1,pt2,(255,0,0))

I know it seems to be simple but I don't have any ideas how to proceed.

Thank you!

Answer 1

Currently your rectangle has no fixed size. Shouldn't it be:

pt1 = (i, j)
pt2 = (pt1.x+20, pt1.y+20)

And additionally you might want to check that the rectangle does not overlap your image.