https://bugzilla.wikimedia.org/show_bug.cgi?id=16451


Robert Rohde <[email protected]> changed:

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--- Comment #6 from Robert Rohde <[email protected]>  2009-02-28 06:35:45 
UTC ---
The first comment in the user notes section at:

http://www.php.net/manual/en/function.imagecreatefromgif.php

provides instructions for determining whether a GIF is animated or not.

It looks for 6 specific bytes as part of a 10 byte sequence that denote the
opening of a new frame header.  Strictly speaking, I believe this will
sometimes misidentify an image as animated when it is not, since the GIF spec
appears to allow the same control bytes to occur within compressed image data
(etc.)  However, getting a 6 byte sequence by accident is a low probability
event in random data.  More importantly, a false positive (that causes a static
image not to be scaled) would appear to be fine from a WMF point of view
provided that one never has false negatives, which I think is correct for the
code sample given.

If the issue is simply that one wants to the detect and disable scaling on
animated GIFs then I believe the code sample at the linked page is adequate for
that purpose.


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