from PIL import Image
image = Image.open("lena.jpg")
buffer=[]
for pixel in image.getdata():
buffer.append((
pixel[0],
pixel[1],
pixel[2],
pixel[3]-150,
))
image.putdata(buffer)
image.save(‘python_filter2.png‘)
change the value of the alpha channel
原文：https://www.cnblogs.com/ax204/p/10761785.html