使用 Python 成像库 (PIL)，如何将带有 alpha 通道的图像合成到另一张图像上?

问题描述

我有两张图片，都带有 alpha 通道.我想将一个图像放在另一个图像上，从而生成一个带有 alpha 通道的新图像，就像它们在图层中渲染一样.我想用 Python Imaging Library 来做到这一点，但在其他系统中的推荐会很棒，即使是原始数学也是一个福音；我可以使用 NumPy.

I have two images, both with alpha channels. I want to put one image over the other, resulting in a new image with an alpha channel, just as would occur if they were rendered in layers. I would like to do this with the Python Imaging Library, but recommendations in other systems would be fantastic, even the raw math would be a boon; I could use NumPy.

推荐答案

我找不到 alphaPIL 中的复合 函数，所以这是我用 numpy 实现它的尝试:

I couldn't find an alpha composite function in PIL, so here is my attempt at implementing it with numpy:

import numpy as np
from PIL import Image

def alpha_composite(src, dst):
    '''
    Return the alpha composite of src and dst.

    Parameters:
    src -- PIL RGBA Image object
    dst -- PIL RGBA Image object

    The algorithm comes from http://en.wikipedia.org/wiki/Alpha_compositing
    '''
    # http://stackoverflow.com/a/3375291/190597
    # http://stackoverflow.com/a/9166671/190597
    src = np.asarray(src)
    dst = np.asarray(dst)
    out = np.empty(src.shape, dtype = 'float')
    alpha = np.index_exp[:, :, 3:]
    rgb = np.index_exp[:, :, :3]
    src_a = src[alpha]/255.0
    dst_a = dst[alpha]/255.0
    out[alpha] = src_a+dst_a*(1-src_a)
    old_setting = np.seterr(invalid = 'ignore')
    out[rgb] = (src[rgb]*src_a + dst[rgb]*dst_a*(1-src_a))/out[alpha]
    np.seterr(**old_setting)
    out[alpha] *= 255
    np.clip(out,0,255)
    # astype('uint8') maps np.nan (and np.inf) to 0
    out = out.astype('uint8')
    out = Image.fromarray(out, 'RGBA')
    return out

例如给定这两张图片，

img1 = Image.new('RGBA', size = (100, 100), color = (255, 0, 0, 255))
draw = ImageDraw.Draw(img1)
draw.rectangle((33, 0, 66, 100), fill = (255, 0, 0, 128))
draw.rectangle((67, 0, 100, 100), fill = (255, 0, 0, 0))
img1.save('/tmp/img1.png')

img2 = Image.new('RGBA', size = (100, 100), color = (0, 255, 0, 255))
draw = ImageDraw.Draw(img2)
draw.rectangle((0, 33, 100, 66), fill = (0, 255, 0, 128))
draw.rectangle((0, 67, 100, 100), fill = (0, 255, 0, 0))
img2.save('/tmp/img2.png')

alpha_composite 产生:

img3 = alpha_composite(img1, img2)
img3.save('/tmp/img3.png')

这篇关于使用 Python 成像库 (PIL)，如何将带有 alpha 通道的图像合成到另一张图像上?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！