perspective_correction.py

import numpy as np
import cv2 as cv

def mouse_event_handler(event, x, y, flags, param):
    if event == cv.EVENT_LBUTTONDOWN:
        param.append((x, y))

if __name__ == '__main__':
    img_file = '../data/sunglok_card.jpg'
    card_size = (450, 250)
    offset = 10

    # Prepare the rectified points
    pts_dst = np.array([[0, 0], [card_size[0], 0], [0, card_size[1]], [card_size[0], card_size[1]]])

    # Load an image
    img = cv.imread(img_file)
    assert img is not None, 'Cannot read the given image, ' + img_file

    # Get the matched points from mouse clicks
    pts_src = []
    wnd_name = 'Perspective Correction: Point Selection'
    cv.namedWindow(wnd_name)
    cv.setMouseCallback(wnd_name, mouse_event_handler, pts_src)
    while len(pts_src) < 4:
        img_display = img.copy()
        cv.rectangle(img_display, (offset, offset), (offset + card_size[0], offset + card_size[1]), (0, 0, 255), 2)
        idx = min(len(pts_src), len(pts_dst))
        cv.circle(img_display, offset + pts_dst[idx], 5, (0, 255, 0), -1)
        cv.imshow(wnd_name, img_display)
        key = cv.waitKey(10)
        if key == 27: # ESC
            break

    if len(pts_src) == 4:
        # Calculate planar homography and rectify perspective distortion
        H, _ = cv.findHomography(np.array(pts_src), pts_dst)
        print(f'pts_src = {pts_src}')
        print(f'pts_dst = {pts_dst}')
        print(f'H = {H}')
        img_rectify = cv.warpPerspective(img, H, card_size)

        # Show the rectified image
        cv.imshow('Perspective Distortion Correction: Rectified Image', img_rectify)
        cv.waitKey(0)

    cv.destroyAllWindows()