Why does the Gimbal shape change?

import numpy as np
import imageio
import scipy
import scipy.signal
import matplotlib.pyplot as plt round = imageio.imread("round.png", as_gray=True)
gibbous = imageio.imread("gibb2.png", as_gray=True)
kern = imageio.imread("kern2.png", as_gray=True) convr = scipy.signal.convolve2d(round, kern, mode='full')
convg = scipy.signal.convolve2d(gibbous, kern, mode='full') convr /= np.max(convr)
convg /= np.max(convg) fig ... Read even more