Last frame of gif has second last frame merged to it

[s0hv]

What did you do?

I iterated through gif frames and added copies of the frames converted to rgba to a list of the following 4 frame gif

This was the code I used and what produced the invalid result

frames = []
while True:
    frames.append(im.copy().convert('RGBA'))
    try:
        im.seek(im.tell() + 1)
    except EOFError:
        break

What did you expect to happen?

Expected that all the frames would look normal without them merging

What actually happened?

The last 2 images merged as in the following pic when the expected result would be
The second last frame was kept normal but the last frame included the second last frame merged to it
I was able to get the desired result by using the following modification of my original loop

frames = []
while True:
    frames.append(im.copy().convert('RGBA'))
    try:
        im.seek(im.tell() + 1)
    except EOFError:
        frames[-1] = im.copy().convert('RGBA')
        break

What versions of Pillow and Python are you using?

Python 3.6.4
Pillow 5.1.0

[radarhere]

GIFs have a value called a 'disposal method'. For the last frame in this image, it is set to 'Do not dispose. The graphic is to be left in place.'

So from what I can see, Pillow is behaving correctly. Clearly standard image viewers have other ideas about what to do in this situation though, and I don't know what logic they are using.

[radarhere]

This is resolved by #3434.

I'm also going to move discussion of #3665 (comment) here, which looks like the same problem, and is also solved by #3434.

import requests
from PIL import Image
response = requests.get('https://66.media.tumblr.com/tumblr_lzkp40b0Sl1qhwcy0.gif')
im = Image.open(BytesIO(response.content))
im.save('1.png', 'PNG')
im.seek(1)
im.load()
im.save('2.png', 'PNG')

The 2.png has second frame pasted onto first.
Expected result is second frame pasted into background (transparent).

[radarhere]

I've created PR #5125 to resolve this.