Lipstick Lipstick - 6 months ago 11
Python Question

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

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')

Answer

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