使用python Wand替换颜色，但坐标未知

from wand.image import Image
from wand.color import Color

with Image(filename='image.jpg') as img:
    # 图像处理代码

width = img.width
height = img.height

for x in range(width):
    for y in range(height):
        # 获取像素颜色
        pixel_color = img[x, y]
        # 判断颜色是否需要替换
        if pixel_color == Color('red'):
            # 替换颜色
            img[x, y] = Color('blue')

img.save(filename='modified_image.jpg')