def inverse_image(img):
    """
    Inverse the image
    Black becomes white
    White becomes black
    """
    for i in range(img.shape[0]):
        for j in range(img.shape[1]):
            if img[i, j] > 255/2.0:
                img[i, j] = 0
            else:
                img[i, j] = 255

    return img