# -*- coding: UTF-8 -*-
from PIL import Image

def add_transparency(img, factor=0.7):
    img = img.convert('RGBA')
    img_blender = Image.new('RGBA', img.size, (252,45,75)) # 填充rgb颜色
    img = Image.blend(img_blender, img, factor)
    return img

img = Image.open("out.png")
img = addTransparency(img, factor=0.7)
img.save('input.png') # 图片另存为
img.show()

参考：Python PIL读取与保存图片