This script tries to find edges of a stereocard based on the algorithm proposed by Martin Schub at https://photo-3d.groups.io/g/main/message/125478

stereocard_find_edges.py

#!/usr/bin/env python3

# This script tries to find edges of a stereocard based on the algorithm
# proposed by Martin Schub at https://photo-3d.groups.io/g/main/message/125478

import sys
import numpy as np
from scipy.signal import argrelmax
from PIL import Image
import matplotlib.pyplot as plt

if len(sys.argv) != 2:
    print('Usage: ' + sys.argv[0] + ' <image>')
    sys.exit(1)

img = Image.open(sys.argv[1]).convert("L")
n = np.array(img)
h0 = np.abs(np.gradient(n.mean(axis=0)))
h1 = np.abs(np.gradient(n.mean(axis=1)))
m0 = h0.mean()
m1 = h1.mean()
max0 = argrelmax(np.maximum(5*m0, h0))[0]
max1 = argrelmax(np.maximum(5*m1, h1))[0]
print(max0, max1)

fig = plt.figure(figsize=(8, 8))
gs = fig.add_gridspec(2, 2,  width_ratios=(7, 2), height_ratios=(2, 7),
        left=0.1, right=0.9, bottom=0.1, top=0.9,
        wspace=0.05, hspace=0.05)

ax = fig.add_subplot(gs[1, 0])
ax_histx = fig.add_subplot(gs[0, 0], sharex=ax)
ax_histy = fig.add_subplot(gs[1, 1], sharey=ax)

ax.imshow(img, cmap="gray")
ax_histx.plot(h0)
ax_histx.plot(max0, h0[max0], ' o')
histyy = np.arange(len(h1))
ax_histy.plot(h1, histyy)
ax_histy.plot(h1[max1], max1, ' o')

plt.show()