harris_demo.py

import numpy as np
from scipy import signal
import matplotlib.pyplot as plt


def myHarris(image):
    """Simple implementation of harris corner detector

    Args:
        image (np.array): gray image 
    """
    sobelx = np.array([[-1, 0, 1],
                       [-2, 0, 2],
                       [-1,  0, 1]])
    sobely = np.array([[-1, -2, -1],
                       [0, 0, 0],
                       [1, 2, 1]])

    Ixx = signal.convolve2d(signal.convolve2d(
        image, sobelx, "same"), sobelx, "same")

    Iyy = signal.convolve2d(signal.convolve2d(
        image, sobely, "same"), sobely, "same")

    Ixy = signal.convolve2d(signal.convolve2d(
        image, sobelx, "same"), sobely, "same")

    plt.figure("Original Image")
    plt.set_cmap("gray")
    plt.imshow(image)

    plt.figure("Ixx")
    plt.imshow(Ixx)

    plt.figure("Iyy")
    plt.imshow(Iyy)

    plt.figure("Ixy")
    plt.imshow(Ixy)

    det = Ixx * Iyy - Ixy**2
    trace = Ixx + Iyy

    H = det - 0.2 * trace

    plt.figure("Harris")
    plt.imshow(np.abs(H))
    plt.show()


if __name__ == '__main__':
    # Create the image
    image = np.zeros((200, 200))
    image[50:150, 50:150] = 255
    # Detect the corners
    myHarris(image)