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List:       imagemagick-developer
Subject:    Re: [magick-developers] SampleImage
From:       "Glenn Randers-Pehrson <glennrp>" <glennrp () comcast ! net>
Date:       2002-04-23 14:57:14
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Bob Friesenhahn wrote:

> On Tue, 23 Apr 2002, Tim McCormick wrote:
>
> > I'm using the Magick 543 C Api to manipulate images. One of the
> > manipulations I am doing is image resizing.  I am using SampleImage to do
> > these resizes, and it works great for all images except multi frame images
> > eg: animated Gif's.
>
> It is important to realize that animated GIFs are not just multi-frame
> images.  The different frames in a animated GIF may have different
> sizes, with a smaller frame being mapped into the viewed image via a
> page offset.  Furthermore, there are GIF disposal methods which
> indicate how the subimage is to be blended with the previously blended
> image data to produce the result.  In effect, GIF animations use the
> sub-frames and disposal methods as a form of compression. GIF images
> require perfect pixel registration, transparency, etc., to produce the
> intended result.  They are a work of art.
>
> Given this, it is extremely difficult to resize a GIF animation and
> achieve usable results.

The -coalesce option should help with all those problems.  You
could then do a second conversion of the resized animation with
the -deconstruct option to avoid including the unchanged portion in
each frame.

Glenn

>

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