python使用PIL制作水印

import Image, ImageEnhance
 
def reduce_opacity(im, opacity):
 """Returns an image with reduced opacity."""
 assert opacity >= 0 and opacity <= 1
 if im.mode != 'RGBA':
 im = im.convert('RGBA')
 else:
 im = im.copy()
 alpha = im.split()[3]
 alpha = ImageEnhance.Brightness(alpha).enhance(opacity)
 im.putalpha(alpha)
 return im
 
def watermark(im, mark, position, opacity=1):
 """Adds a watermark to an image."""
 if opacity < 1:
 mark = reduce_opacity(mark, opacity)
 if im.mode != 'RGBA':
 im = im.convert('RGBA')
 # create a transparent layer the size of the image and draw the
 # watermark in that layer.
 layer = Image.new('RGBA', im.size, (0,0,0,0))
 if position == 'tile':
 for y in range(0, im.size[1], mark.size[1]):
 for x in range(0, im.size[0], mark.size[0]):
 layer.paste(mark, (x, y))
 elif position == 'scale':
 # scale, but preserve the aspect ratio
 ratio = min(
 float(im.size[0]) / mark.size[0], float(im.size[1]) / mark.size[1])
 w = int(mark.size[0] * ratio)
 h = int(mark.size[1] * ratio)
 mark = mark.resize((w, h))
 layer.paste(mark, ((im.size[0] - w) / 2, (im.size[1] - h) / 2))
 else:
 layer.paste(mark, position)
 # composite the watermark with the layer
 return Image.composite(layer, im, layer)
 
def test():
 im = Image.open('test.png')
 mark = Image.open('overlay.png')
 watermark(im, mark, 'tile', 0.5).show()
 watermark(im, mark, 'scale', 1.0).show()
 watermark(im, mark, (100, 100), 0.5).show()
 
if __name__ == '__main__':
 test()