如何在python中多进程遍历每个像素的for循环？

import multiprocessing as mp
from PIL import Image

def process_pixel(args):
    x, y, img = args
    pixel_value = img.getpixel((x, y))
    # 这里可以进行像素值的处理
    processed_value = pixel_value * 2  # 示例处理：将像素值乘以2
    return (x, y, processed_value)

def main(image_path):
    img = Image.open(image_path)
    width, height = img.size
    pixels = [(x, y, img) for x in range(width) for y in range(height)]
    
    with mp.Pool(mp.cpu_count()) as pool:
        results = pool.map(process_pixel, pixels)
    
    # 将处理后的像素值写回图像
    for x, y, value in results:
        img.putpixel((x, y), value)
    
    img.save('processed_image.jpg')

if __name__ == '__main__':
    main('input_image.jpg')