Ever wonder why software is so slow...?

Because it's all written by retards.

https://github.com/ArtifexSoftware/jbig2dec/blob/master/jbig2_image.c

Scroll down to jbig2_image_compose_unopt()... and then facepalm. It doesn't take a genius to realise that twiddling an image pixel-by-pixel is going to be dead slow.

>>8
Due to licensing crap I can't, but give me a day or two and I'll write something up on a pastebin which you can try.

Browser is a background thing, at the moment there's plenty of more important stuff to work on.

>>9,10
Try some of the big ebook scans on archive.org . MuPDF's vector graphics rendering is fast enough, but it chokes severely on pages with JBIG2/JPEG2000 images.

>>15-19
CPUs can work in far bigger chunks than bits. The partially optimised code (for the OR caes only, how strange) works with bytes, but you can do bigger than that.

Actually it should be possible to replace all that code with a single BitBlt() call, which as far as I know is GPU accelerated, but Windows-only.