Loss of data when extracting frames from GIF to PNG?

问题

When I try to use fraxel's answer on

http://stackoverflow.com/questions/10269099/pil-convert-gif-frames-to-jpg

on the image http://24.media.tumblr.com/fffcc2d8e980fbba4f87d51ed4916b87/tumblr_mh8uaqMo2I1rkp3avo2_250.gif

I get ok data for some, but then for some I get missing data it looks like, e.g.

Correct

Missing

To display these I use imagemagick's display foo* and then use space to move through the images ... is it possible imagemagick is reading them wrong?

Edit:

Even when using convert and then displaying via display foo* I get the following

Could this be a characteristic of the gif then?

回答1:

If you can stick to ImageMagick then it is very simple to solve this:

convert input.gif -coalesce output.png

Otherwise, you will have to consider the different forms of how each GIF frame can be constructed. For this specific type of GIF, and also the other one shown in your other question, the following code works (note that in your earlier question, the accepted answer doesn't actually make all the split parts transparent -- at least with the latest released PIL):

import sys
from PIL import Image, ImageSequence

img = Image.open(sys.argv[1])

pal = img.getpalette()
prev = img.convert('RGBA')
prev_dispose = True
for i, frame in enumerate(ImageSequence.Iterator(img)):
    dispose = frame.dispose

    if frame.tile:
        x0, y0, x1, y1 = frame.tile[0][1]
        if not frame.palette.dirty:
            frame.putpalette(pal)
        frame = frame.crop((x0, y0, x1, y1))
        bbox = (x0, y0, x1, y1)
    else:
        bbox = None

    if dispose is None:
        prev.paste(frame, bbox, frame.convert('RGBA'))
        prev.save('foo%02d.png' % i)
        prev_dispose = False
    else:
        if prev_dispose:
            prev = Image.new('RGBA', img.size, (0, 0, 0, 0))
        out = prev.copy()
        out.paste(frame, bbox, frame.convert('RGBA'))
        out.save('foo%02d.png' % i)

Ultimately you will have to recreate what -coalesce does, since it is likely that the code above may not work with certain GIF images.

回答2:

You should try keeping the whole history of frames in "background", instead of :

background = Image.new("RGB", size, (255,255,255))
background.paste( lastframe )
background.paste( im2 )

Just create the "background" once before the loop, then only paste() frame on it, it should work.

来源：https://stackoverflow.com/questions/14550055/loss-of-data-when-extracting-frames-from-gif-to-png