TypeError: unsupported operand type(s) for -: 'tuple' and 'tuple'

debugcn Published at Dev

Lipstick

I try to use Moravec detection. When I try to run this code I get some error:

     diff = diff - image.getpixel((x, y))
TypeError: unsupported operand type(s) for -: 'tuple' and 'tuple'

How can I fix it? Any help will be appreciated. The code is:

def moravec(image, threshold = 100):
    """Moravec's corner detection for each pixel of the image."""

    corners = []
    xy_shifts = [(1, 0), (1, 1), (0, 1), (-1, 1)]

    for y in range(1, image.size[1]-1):
        for x in range(1, image.size[0]-1):
            # Look for local maxima in min(E) above threshold:
            E = 100000
            for shift in xy_shifts:
                diff = image.getpixel((x + shift[0], y + shift[1]))
                diff = diff - image.getpixel((x, y))
                diff = diff * diff
                if diff < E:
                    E = diff
            if E > threshold:
                corners.append((x, y))

    return corners

if __name__ == "__main__":
        threshold = 100

        image = Image.open('all.jpg')
        corners = moravec(image, threshold)
        draw_corners(image, corners)
        image.save('low2.png')

aldanor

You're trying to substract two tuples (with RGB values), and arithmetic operations on tuples like * and - are not defined.

To find the distance, you could just do this:

c1 = image.getpixel((x + shift[0], y + shift[1]))
c2 = image.getpixel((x, y))
diff = (c1[0] - c2[0]) ** 2 + (c1[1] - c2[1]) ** 2 + (c1[2] - c2[2]) ** 2
if diff < E:
    E = diff

Hypothetically also could use numpy to get the dot products and arithmetic operations working out of the box if that's what you're used to, although it's a bit of an overkill:

import numpy as np

c1 = image.getpixel((x + shift[0], y + shift[1]))
c2 = image.getpixel((x, y))
diff = (np.diff([c1, c2]) ** 2).sum()
if diff < E:
    E = diff

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