--optimize switch corrupts output about gifsicle

[kohler]

This was an interesting bug. I think I’ve fixed it in commit 6c1a18c. Please let me know if you observe more issues.

[daxim]

Yes, with master branch at commit 6c1a18c the pixel at 1313,892 is still wrong at -O2 or higher. It is marked with a small circle in the overview image above.

[kohler]

Are you sure? I'm not actually seeing this.

On Wed, Dec 3, 2014 at 7:56 AM, Lars Dɪᴇᴄᴋᴏᴡ 迪拉斯 [email protected]
wrote:

Yes, with master branch at commit 6c1a18c
6c1a18c
the pixel at 1313,892 is still wrong at -O2 or higher. It is marked with
a small circle in the overview image above
https://cloud.githubusercontent.com/assets/104814/5202004/a1a095b2-7579-11e4-94a8-78d6480c561a.png
.

—
Reply to this email directly or view it on GitHub
#31 (comment).

[daxim]

I am sure.

Steps to reproduce:

1. Check out repo, verify that HEAD is 6c1a18c:

   $ git clone [email protected]:kohler/gifsicle.git
   $ cd gifsicle
   $ git show --oneline HEAD | head -1
   6c1a18c Always optimize as if the background is transparent.
   

2. Compile and install:

   $ sh bootstrap.sh
   $ ./configure --enable-all --prefix=/tmp/gifsicle168
   $ make install
   

3. Get test case input image:

   $ git clone [email protected]:/4e66de28b447a1ca851f.git
   $ cd 4e66de28b447a1ca851f
   

4. Generate output as in the top post of this bug report:

   $ /tmp/gifsicle168/bin/gifsicle -O1 haenau.gif > haenau-O1.gif
   $ /tmp/gifsicle168/bin/gifsicle -O2 haenau.gif > haenau-O2.gif
   $ /tmp/gifsicle168/bin/gifsicle -O3 haenau.gif > haenau-O3.gif
   

5. View the haenau-O2.gif image in Firefox 33 (libporn GIF decoder) and Gwenview 4.14 (QImageReader GIF decoder), set image scaling to 1:1 (because both default to rescale-to-window) and observe the pixel at coordinates 1313,892 relative to the top-left corner of the image.

Expected:

Pixel has the colour #0411b8, a deep blue.

Actual:

Pixel has the colour #ffffff, bright white.

[kohler]

OK. I can confirm that I see the bad pixel on Firefox.

However, I do not see the bad pixel in Gifview (bundled with Gifsicle), in Safari, or in Chrome.
Gifdiff believes the files are equivalent except for background color.
And when I give the --careful option to gifsicle -O2, no bad pixel.

I'm not sure whether this is an encoding bug in Gifsicle or a bug in other gif libraries.

[kohler]

The following command:

gifsicle -O2 haenau.gif

produces a GIF that Firefox displays with a bad pixel. But this:

gifsicle -O2 --delay=1 haenau.gif

produces a GIF with no bad pixel. This is strong evidence that the bug is in Firefox since the encoded image data is the same in both cases.

[daxim]

That's compelling. I'll file further bugs with the aforementioned software projects.

I'd like you to:

• mark this bug as stalled
• cut a release with the fixes so far so that I can tell people to get v1.87 to reproduce the problem.

[kohler]

OK, I released 1.87.

[kohler]

Hey, I'd like to close this issue unless it's still active.

[daxim]

Closing. The bugs I filed on Firefox and Gwenview last year have not progressed, unfortunately.