import cv2
import numpy as np
import PIL

def preprocess_canny(img: PIL.Image) -> PIL.Image:
    image_to_canny = np.array(img)
    image_to_canny = cv2.Canny(image_to_canny, 100, 200)
    image_to_canny = np.array(image_to_canny[:, :, None])
    image_to_canny = np.concatenate([image_to_canny, image_to_canny, image_to_canny], axis=2)
    return PIL.Image.fromarray(image_to_canny)