I dunno about GIMP ...
A lot of filters only work on RGB or some specific color mode.
If you can access each frame of the GIF, you can convert to RGB and apply your filter individually.
You can then take all the frames and recompile them in to an animated GIF using one of the bazillion Gif utils out there. On recompile, the colors will be reintegrated into a new index.
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In GIMP, it is Image->Mode->RGB.Originally Posted by töff
To change specific colours you can play with Colours->Hue Saturation or Colurs->Map->Rotate Colours
You will have to re-dither/quantify down to 256 colours again. The biggest problem with GIF animations is ensuring each frame has the same dither pattern or you will inadvertently end up with glitter.
-Rob A>
Last edited by RobA; 04-27-2010 at 08:43 PM.
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You could have another quick run through my tech tut. In there it explains a little about formats. Specifically in this case all GIF type images are paletted to a maximum of 256 colours so when you have a GIF anim you can extract all the frames from it but they will all be up to 256 colours. To do special processing on images you normally need full color or true color mode which is a byte per pixel or 24 bit or 16 million colours.
You can upsample the colours in the frames from 8 to 24 bit but out of the range of possible 16 million it will still use 256 of them until you start to blur or do some processing. The issue is that once all finished you will probably want to get it back into a GIF again and then you must down sample the colours from 24 bits back 8 again.
There's not a lot of options tho. The not completely new browsers don't support animated PNG format - the MNG format which does do RGBA animations and whilst firefox, opera etc will support that as does windows picture and fax viewer, I was not sure about IE. Last time I tried it didn't but I cant see why it should not now.
Incidentally ImageMagick will generate MNG files from a series of PNGs if you want to try.
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