Best quality dithering library in C

Question

I'm developing a texture atlas packer to use with OpenGL, and I'm currently looking for an open-source (it's better if it's a library, but an open-source software would be good as well!) solution that will render the best results for color palette creation / dithering. It really doesn't need to be fast, but needs to achieve optimal results. It would be best if there is a possibility for 4-bit-per-pixel palette generation.

Answer 1

pngquant is available as a pure C library.

ImageMagick uses octtree, which is fast, but not the best quality.

pngquant uses MedianCut with several additional improvements, and is likely to give higher quality.

pngquant has speed/quality trade-off setting which can improve quality a bit further, and also has custom dithering algorithm (variation of Floyd-Steinberg) that doesn't add noise to well-quantized areas of the image.

Answer 2

Imagemagick is a very powerful C library for graphical manipulation: http://www.imagemagick.org/ It has commandline tools, but can also be used as a C library.

Answer 3

For future reference, I found PNGNQ, which is a pretty good library for image quantization. Their samples are amazing.