Python - cv2 - imshow and waitKey (Stackoverflow)

# date: 2025.12.29

# [opencv - How to fix this code so it shows the image with python and cv? - Stack Overflow](https://stackoverflow.com/questions/79856626/how-to-fix-this-code-so-it-shows-the-image-with-python-and-cv)

import cv2
import numpy as np
import time


# ---------------- CONFIG ----------------
BASE_IMAGE_PATH = "Input/RIMG_20250222_074457.jpg"
OVERLAY_IMAGE_PATH = "Input/RIMG_20250308_072815.jpg"
# BASE_IMAGE_PATH = "image1.jpg"
# OVERLAY_IMAGE_PATH = "image2.jpg"
OUTPUT_IMAGE_PATH = "overlay_aligned.png"

MOVE_STEP = 5  # pixels per key press
ROTATE_STEP = 1.0  # degrees per key press
ZOOM_STEP = 0.02  # scale per key press
# ---------------------------------------


def transform_overlay(img, tx, ty, angle, scale):
    print("rendering ...")
    h, w = img.shape[:2]

    # Center of the image
    center = (w // 2, h // 2)

    # Rotation + scaling
    M = cv2.getRotationMatrix2D(center, angle, scale)

    # Translation
    M[0, 2] += tx
    M[1, 2] += ty

    transformed = cv2.warpAffine(
        img,
        M,
        (w, h),
        flags=cv2.INTER_LINEAR,
        borderMode=cv2.BORDER_CONSTANT,
        borderValue=(0, 0, 0),
    )

    return transformed, M


def main():
    base = cv2.imread(BASE_IMAGE_PATH)
    overlay = cv2.imread(OVERLAY_IMAGE_PATH)

    if base is None or overlay is None:
        raise FileNotFoundError("Could not load images")

    # Resize overlay to match base if needed
    overlay = cv2.resize(overlay, (base.shape[1], base.shape[0]))

    tx, ty = 0, 0
    angle = 0.0
    scale = 1.0

    print("Controls:")
    print("Arrow keys: move overlay")
    print("A / D: rotate")
    print("W / S: zoom in / out")
    print("R: reset")
    print("SPACE: save aligned overlay")
    print("ESC: exit")

    cv2.namedWindow("Alignment Tool", cv2.WINDOW_NORMAL)

    while True:
        transformed, M = transform_overlay(overlay, tx, ty, angle, scale)
        # Blend images for visualization
        blended = cv2.addWeighted(base, 0.6, transformed, 0.4, 0)

        cv2.imshow("Alignment Tool", blended)

        key = cv2.waitKey(100)  # 100ms = 0.1s

        print(key)

        if key != -1:
            if key == 27:  # ESC
                break

            elif key == ord("r"):
                tx, ty, angle, scale = 0, 0, 0.0, 1.0

            elif key == ord("a"):
                angle -= ROTATE_STEP
            elif key == ord("d"):
                angle += ROTATE_STEP

            elif key == ord("w"):
                scale += ZOOM_STEP
            elif key == ord("s"):
                scale = max(0.1, scale - ZOOM_STEP)

            elif key == 32:  # SPACE
                cv2.imwrite(OUTPUT_IMAGE_PATH, transformed)
                print(f"Saved aligned overlay to {OUTPUT_IMAGE_PATH}")

            # Arrow keys (OpenCV key codes)
            elif key == ord("j"):  # left
                tx -= MOVE_STEP
            elif key == ord("k"):  # right
                tx += MOVE_STEP
            elif key == ord("i"):  # up
                ty -= MOVE_STEP
            elif key == ord("m"):  # down
                ty += MOVE_STEP

    cv2.destroyAllWindows()


if __name__ == "__main__":
    main()