[KevinH]

@Tex2000ans,

As for colour depth, does setting max number of colours to anything other than a power of 2 make sense? Ie. why 17 colours for your equations? I could see space savings from using 16 colours each represented as 4 bit wide fields with two fields packed into a single byte, but non-powers of 2 would seem to drop colour range with no associated space saving. Or am I missing something?

BTW, I found a program on github called pngquant2 that seems to be using k-means cluster analysis on colours to determine true number of degrees of freedom represented by the colours actually used to determine the "best" set of palette colours to choose. Is this what Gimp is doing with the Index and Optimize approach you mentioned? Or is that something else?

Edit: tried pngquant2 with high compression and Gimp using the Indexing with Optimize colours you pointed out, and Gimp saved about 12k in final size and appears equal visually.

Web and e-readers really do benefit in many ways from smaller image file sizes (loading speed, number of files cached for reload, memory footprint, etc) that print versions needing super high quality really do not need to worry about or benefit from ... thus making a quality vs filesize tradeoff important. Even from a network bandwidth for people downloading the epub given how many people that repeatedly. That makes the whole choice of tradeoff quite subjective in many ways.

If you feel that some specific images in the user guide had gone too far in that tradeoff, please let us know.

Thanks,

Kevin