如何使用 python 的枕头使裁剪后的 gif 角透明？

Question

I'm trying to edit an avatar image from my discord users with a GaussianBlur filter, crop it to a circle and overlay an image. So all of these things work, but the cropped gifs have corners, I don't want them. It should be transparent. I searched a lot for a solution but can't find it. I'm inexperienced in coding with python's pillow library and don't know how I could fix it.

My current code transforms this (PICTURE 1):

into this (PICTURE 2):

but it should be this (working for static images but GIFs should keep their animation at the end):

Like you can see my cropped GIF image has white corners. It doesn't contain them if PICTURE 1 is a PNG. So how can I remove these white corners?

And that is my currently used code:

    def crop_center(pil_img, crop_width, crop_height):
        img_width, img_height = pil_img.size
        return pil_img.crop(((img_width - crop_width) // 2,
                             (img_height - crop_height) // 2,
                             (img_width + crop_width) // 2,
                             (img_height + crop_height) // 2))
    
    def crop_max_square(pil_img):
        return crop_center(pil_img, min(pil_img.size), min(pil_img.size))
    
    def mask_circle_transparent(pil_img, blur_radius, offset=0):
        offset = blur_radius * 2 + offset
        mask = Image.new("L", pil_img.size, 0)
        draw = ImageDraw.Draw(mask)
        draw.ellipse((offset, offset, pil_img.size[0] - offset, pil_img.size[1] - offset), fill=255)
        mask = mask.filter(ImageFilter.GaussianBlur(blur_radius))
    
        result = pil_img.copy()
        result.putalpha(mask)
    
        return result


    async def on_message(message):

       if ".gif" in str(message.author.avatar_url):

          frames = []

          gif = Image.open(BytesIO(await message.author.avatar_url.read()))

          for frame in ImageSequence.Iterator(gif):
              frame = frame.copy()
              frame = frame.convert("RGB")
              frame = frame.resize((256, 256))
              frame = mask_circle_transparent(frame, 4)

              background = background.resize((256, 256))

              frame.paste(background, (0, 0), background)
              frames.append(frame)

              print(str(frames))
              frames[0].save('temp_images/result.gif', save_all=True, append_images=frames[1:])

       else:

          im_square = crop_max_square(Image.open(BytesIO(await message.author.avatar_url.read())).convert("RGB"))
          im_square = im_square.resize((256, 256))
          im_thumb = mask_circle_transparent(im_square, 4)

          background = background.resize((256, 256))

          im_thumb.paste(background, (0, 0), background)
          im_thumb.show()

          im_thumb.save('temp_images/result.png')

Edit: I tested a lot now and I think frame = mask_circle_transparent(frame, 4) is the issue here, before I call that function is my frame is blank, just a background. I don't know why. And apparently, the corners aren't white, it's a color from the image background or something like this? I don't know.

Answer 1

gif does not support transparency. To feather/soften the edges on your gif you may have to use a white overlay layer with feathered edges instead of a mask.

Answer 2

Making the smooth edges is not possible using the GIF format. GIF does not have an alpha channel, so partially transparency is not supported (source: How to get better transparency with GIFs? ). This means that the result you achieved on the static image cannot be achieved on a moving GIF.

However, the background in the GIF can be made transparent using this answer: transparent background in gif using Python Imageio . Below you find the resulting GIF and the code to achieve this result. (I had to skip a few parts of your code, since I did not have the background image and the Discord connection).

from PIL import Image, ImageDraw, ImageFilter, ImageSequence
import numpy as np

def crop_center(pil_img, crop_width, crop_height):
    img_width, img_height = pil_img.size
    return pil_img.crop(((img_width - crop_width) // 2,
                         (img_height - crop_height) // 2,
                         (img_width + crop_width) // 2,
                         (img_height + crop_height) // 2))

def crop_max_square(pil_img):
    return crop_center(pil_img, min(pil_img.size), min(pil_img.size))

def mask_circle_transparent(pil_img, blur_radius, offset=0):
    offset = blur_radius * 2 + offset
    mask = Image.new("L", pil_img.size, 0)
    draw = ImageDraw.Draw(mask)
    draw.ellipse((offset, offset, pil_img.size[0] - offset, pil_img.size[1] - offset), fill=255)
    mask = mask.filter(ImageFilter.GaussianBlur(blur_radius))

    result = pil_img.copy()
    result.putalpha(mask)

    return result


def transparent_frame(im):
    # im = Image.open(path)
    alpha = im.getchannel('A')

    # Convert the image into P mode but only use 255 colors in the palette out of 256
    im = im.convert('RGB').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
    im.paste(255, mask)

    # The transparency index is 255
    im.info['transparency'] = 255

    return im


def on_message(message):

   # if ".gif" in str(message.author.avatar_url):

      frames = []

      gif = Image.open('a.gif')

      for frame in ImageSequence.Iterator(gif):
          frame = frame.copy()
          frame = frame.convert("RGB")
          frame = frame.resize((256, 256))
          frame = mask_circle_transparent(frame, 4)

          # I did not have the background image that you used, so i skipped this part
          # background = background.resize((256, 256))
          # frame.paste(background, (0, 0), background)
          
          # make transparent using the transparent_frame() function
          frame = transparent_frame(frame)
          frames.append(frame)

          # print(str(frames))
          frames[0].save('result.gif', save_all=True, append_images=frames[1:], optimize=False) # optimize must be false to preserve the transparent channel

   # else:

   #    im_square = crop_max_square(Image.open(BytesIO(await message.author.avatar_url.read())).convert("RGB"))
   #    im_square = im_square.resize((256, 256))
   #    im_thumb = mask_circle_transparent(im_square, 4)

   #    background = background.resize((256, 256))

   #    im_thumb.paste(background, (0, 0), background)
   #    im_thumb.show()

   #    im_thumb.save('temp_images/result.png')
   
if __name__ == "__main__":
    on_message('hi')

Answer 3

GIF animations consist of multiple frames, that your image viewer cycles through to give the impression of a video or animation.

As such, you need to read each frame and apply your processing to it, then pass a list of frames to save at the end.

See here for reading an animated GIF, and here for writing.