def mean_threshold(image: Image) -> Image:
    height, width = image.size
    mean = 0
    pixels = image.load()
    for i in range(width):
        for j in range(height):
            pixel = pixels[j, i]
            mean += pixel
    mean //= width * height

    for j in range(width):
        for i in range(height):
            pixels[i, j] = 255 if pixels[i, j] > mean else 0
    return image