[MarjaE]

If you have clear lines, or plenty of black and white, then using Willus's k2pdfopt can work pretty well.

I use a Kindle Dx for the larger screen and k2pdfopt -mode copy -dev dx. It can be hard to get a Dx though.

If you have a lot of saturated colors, it's more challenging. I have tried adding -g 1.0 which avoids turning all colors black, but leaves text spindly and hard to read.

P.S. I tried k2pdfopt -mode copy -dev dx -g 1.0 -er 1 but black text was overdone and white text was obscured. -er 0.5 is not allowed. Maybe -cmax tweaks would work better.