def left_stitch(self, a, b, flag=None):
if flag == 1:
m = Matching('./lib/lib1.jpg', './lib/lib2.jpg')
m.ransac(100)
H_inv = m.H
H = self.matcher.match(a, b, 'left')
H_inv = np.linalg.inv(H)
# find top left point for offset calculation.
tl = np.dot(H_inv, np.array([0, 0, 1]))
tl = tl / tl[-1]
H_inv[0][-1] += abs(tl[0])
H_inv[1][-1] += abs(tl[1])
# find down right for size calculation.
w, h = a.shape[1], a.shape[0]
dr = np.dot(H_inv, np.array([w, h, 1]))
dsize = (int(dr[0]) + abs(int(tl[0])), int(dr[1]) + abs(int(tl[1])))
# warp a into b's view and put them together.
merge = cv2.warpPerspective(a, H_inv, dsize)
fig = plt.figure()
ax1 = fig.add_subplot(1, 2, 1)
plt.imshow(merge)
ax2 = fig.add_subplot(1, 2, 2)
merge[abs(int(tl[1])):b.shape[0] + abs(int(tl[1])),
abs(int(tl[0])):b.shape[1] + abs(int(tl[0])), :] = b
plt.imshow(merge)
plt.show()
offset = (abs(int(tl[0])), abs(int(tl[1])))
return merge, offset
