Finds the transformations between two images given the control points

homography.py

#!/usr/bin/env python

import argparse
import numpy as np
import cv2 as cv

key = None
img = None
coordinates = {
    'src': [],
    'dst': [],
}

def mark_keypoints(event, x, y, flag, param):
    global coordinates, key

    if event == cv.EVENT_LBUTTONDOWN:
        cv.circle(img, (x, y), 10, (0, 255, 0), -1)
        coordinates[key].append([x, y])


def get_keypoints(image, name):
    global key, coordinates, img
    key = name

    cv.namedWindow(key, cv.WINDOW_NORMAL)
    cv.setMouseCallback(key, mark_keypoints)

    img = image.copy()
    while True:
        cv.imshow(name, img)
        k = cv.waitKey(20) & 0xFF
        if k == 27:
            break

    img = None
    return coordinates[key]
    

def main(args):
    im_src = cv.imread(args.src)
    im_dst = cv.imread(args.dst)

    kp_src = get_keypoints(im_src, 'src')
    kp_dst = get_keypoints(im_dst, 'dst')

    kp_src, kp_dst = np.array(kp_src), np.array(kp_dst)
    h, status = cv.findHomography(kp_src, kp_dst)
    im_warp = cv.warpPerspective(im_src, h, im_dst.shape[:2][::-1])

    im_out = cv.addWeighted(im_dst, 0.3, im_warp, 0.7, 0.0)

    cv.destroyAllWindows()
    cv.namedWindow('warp', cv.WINDOW_NORMAL)
    cv.imshow('warp', im_out)
    cv.waitKey(0)


if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('--src', type=str, required=True)
    parser.add_argument('--dst', type=str, required=True)

    args = parser.parse_args()
    main(args)