Thread: Optimize PDFs from archive.org for E-Ink devices
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Old 03-01-2020, 01:35 PM   #23
j.p.s
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Quote:
Originally Posted by j.p.s View Post
One form of archive.org book files have a mask image for each page that can be used to make white regions of the page completely white. Have you ever used those to help clean up the page?
Quote:
Originally Posted by willus View Post
Interesting. No--I had not heard of this before.
It's been a couple of years since I've worked with them, so I'm fuzzy on the details. I mentioned it in passing in post #3 in the thread
https://www.mobileread.com/forums/sh...d.php?t=178155
Some scripts working with the mask images are in the first attachment.

The images (of pages of text) in at least some archive.org PDF files are combinations of 2 PBM images and a PGM image. One of the PBM images is the mask. I discovered this when I ran a utility to extract images from a PDF and have no idea how the PDF standard addresses this or how PDF libraries and utilities make use of the mask images.
Last edited by j.p.s; 03-01-2020 at 01:38 PM.
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