It is just one of the limitations of the index mode which is why their file size is smaller
In reply to my question, sent at 9:03 PM 3/30/02 -0800:
I'm trying to reduced the file-size of the final images by indexing them before saving as PNG's. But when I try indexing the image, most of the anti-aliasing and other "fuzziness" pixels are gone.
Thanks for replying.
I think my confusion stems from my target format, PNG (Portable Network Graphics). This format supports an alpha channel (variable transparency) in its indexed mode, called RGBA, so I just assumed that the GIMP's indexed format would support the same. I'm no expert but it appears that the GIMP's internal, indexed format makes some assumptions about the target format (such as binary transparency and the maximum 256-color palette, probably a design influence from the older, widely used GIF format). Hopefully, over time, the GIMP's indexed format will be more generous so that the newer indexed file formats, like PNG, can be used to full advantage. Then, the final conversion to the desired image format would be the place where output format limitations would be dealt with.
One great web application for PNG indexed graphics is very small images for use as bullets, buttons, icons, and such. Having an A(lpha) channel along with the conventional R, G, and B channels produces beautiful, anti-aliased, small graphics which are not dependent on the background color (unlike GIMP's Semi-Flatten filter). And because they're indexed the cost in file-size is small.
PNG is really gaining ground. The newest Netscape Navigator and Opera browsers fully support both true-color and indexed PNG. Unfortunately the newest Internet Explorer is still weak in this area. PNG's do not support multi-part, animated graphics. For this application there is a companion format being developed called MNG (Multiple-image Network Graphics). MNG is also specified to support transparent JPEG's, an interesting concept.
Sorry if this got a bit wordy. Thanks again,
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