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I have a gif file with a round logo on top of transparent background. The border around the round item needs to be antialiased.

I have tried selecting with the fuzzy wand as well as with border: 2px, but either case I'm not able to choose Color to Alpha nor Blur Gaussian Blur as suggested in many tutorials.

I have also tried changing the format of the file to xcf

Any ideas? Gimp 2.6.12 on Ubuntu 12.04

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The GIF specifications do not allow semi-transparency which would be needed for anti-aliasing a border to the transparent background.

To overcome this you may generate a fake semi-transparency by dithering the output on exporting to GIF (see my answer to this question: GIF with transparency output not as expected in GIMP). The resulting image qualtity may be far from expected. In case you are not happy you will need to use another image format supporting semi-transparency (e.g. PNG).

To be able to use the Blur filters, and then to add an alpha channel we will have to convert the Image > Mode from Indexed... to RGB first.

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