image_file.py 文件源码

def alpha_blend(img, background=255):
        """
        Take an image, assume the last channel is a alpha channel and remove it
        by using the appropriate background.

        :param img:        The image to alpha blend into given background.
        :param background: The background color to use when alpha blending.
                           A scalar is expected, which is used for all
                           the channels.
        """
        alpha = img[..., -1] / 255.0
        channels = img[..., :-1]
        new_img = numpy.zeros_like(channels)
        for ichan in range(channels.shape[-1]):
            new_img[..., ichan] = numpy.clip(
                (1 - alpha) * background + alpha * channels[..., ichan],
                a_min=0, a_max=255)
        return new_img