实现图像缩放线性映射

image_size = (300,300)
total_pixels = image_size[0] * image_size[1]
square_count = 30 #<1>
square_width = 10

def ij(n):
    return (n // image_size[0], n % image_size[1])

def to_lowres_grayscale(img): #<2>

    matrix = [
        [0 for i in range(0,square_count)]
        for j in range(0,square_count)
    ]
    for (n,p) in enumerate(img.pixels):
        i,j = ij(n)
        weight = 1.0 / (3 * square_width * square_width)
        matrix[i // square_width][ j // square_width] += (sum(p) * weight)
    return matrix

def from_lowres_grayscale(matrix): #<3>
    def lowres(pixels, ij):
        i,j = ij
        return pixels[i // square_width][ j // square_width]
    def make_highres(limg):
        pixels = list(matrix)
        triple = lambda x: (x,x,x)
        return ImageVector([triple(lowres(matrix, ij(n))) for n in range(0,total_pixels)])
    return make_highres(matrix)