I've downloaded some files from the Internet Archive. They come in different file formats and most of the time I use PDF. However, sometimes the scans are saved in colour instead of black & white. This makes it difficult (or impossible) to read on a dedicated e-book reader. In that case I downloaded the DjVu files, as on the PC you can select which layer (colour, bw, foreground, background) one would like to see.
Selecting black & white gives excellent results. However, the e-book reader does not have this option.
The question is, how can I remove or extract a layer from the DjVu file and save only this layer?
So far I've tried the following two approaches:
Select black & white in the DjVu viewer on the PC and print to a PostScript file. Followed by a
ps2pdfconversion. This works, but generates a fairly large PDF file. Sure, I can again upload it to any2DjVu but it just seems to much manual work for each file.
I tried the shared annotation feature and said "mode bw". This works on the PC as desired but is ignored on the e-book reader as the other layers are still present.