PySmile Transparency Preservation: Implementation Details

README.md

Check out this project: https://github.com/vietlq/PySmile

The gist is for blog about PySmile Transparency Preservation

alpha_to_color.py

def alpha_to_color(image, color=(255, 255, 255)):
    """Set all fully transparent pixels of an RGBA image to the specified color.
    This is a very simple solution that might leave over some ugly edges, due
    to semi-transparent areas. You should use alpha_composite_with color instead.
    Source: http://stackoverflow.com/a/9166671/284318
    Keyword Arguments:
    image -- PIL RGBA Image object
    color -- Tuple r, g, b (default 255, 255, 255)
    Remember to convert to RGB before saving to non-RGBA formats:
    new_im = im.convert('RGB')
    """
    x = np.array(image)
    r, g, b, a = np.rollaxis(x, axis=-1)
    r[a == 0] = color[0]
    g[a == 0] = color[1]
    b[a == 0] = color[2]
    x = np.dstack([r, g, b, a])
    return Image.fromarray(x, 'RGBA')

convert_to_palette.py

def convert_to_palette(image):
    """Convert transparent image to GIF
    Reference: http://www.pythonclub.org/modules/pil/convert-png-gif
    """
    # Needed for split()
    image.load()
    # Get the alpha band
    alpha = image.split()[3]
    # To have best quality, have non-destructive RGBA to RGB conversion first
    background = pure_pil_alpha_to_color_v2(image)
    # Convert to palette format
    background = background.convert('P', palette=Image.ADAPTIVE, colors=255)
    # Set all pixel values below 128 to 255, and the rest to 0
    mask = Image.eval(alpha, lambda a: 255 if a <= 128 else 0)
    # Paste the color of index 255 and use alpha as a mask
    background.paste(255, mask)
    return background

pure_pil_alpha_to_color_v2.py

def pure_pil_alpha_to_color_v2(image, color=(255, 255, 255)):
    """Alpha composite an RGBA Image with a specified color.
    Simpler, faster version than the solutions above.
    Source: http://stackoverflow.com/a/9459208/284318
    Keyword Arguments:
    image -- PIL RGBA Image object
    color -- Tuple r, g, b (default 255, 255, 255)
    """
    image.load()  # needed for split()
    background = Image.new('RGB', image.size, color)
    background.paste(image, mask=image.split()[3])  # 3 is the alpha channel
    return background