Am 21.02.2018 um 16:39 schrieb Gunter Königsmann:
Normally if you set the white level low enough that the paper is "white"
and the black level high enough that the letters are completely black
and if you set the scan to 1 bit color depth and tell scantailor to
suppress all speckles that are less than 4 pixels wide png compression
should result in smaller files than a JPEG compression that is lossy
enough to produce ringing at every change from black to white and vice
I have considered such an approach.
Issue is that not everything is text in the books, there's the
occasional rare image. But even these few pages would force me to look
at each page manually whether it needs to be stored at full resolution,
or with different compression options. Since I have a six-digit number
of pages to look at, this would be a *lot* of work, for a sub-percent
amount of pages.
The other consideration is that I want to keep my OCR options. Maybe
some future OCR suite is more accurate than Tesseract, but exploits
exactly the kind of redundancy that JPG kills with its artifacts.
So I do have a preference for lossless compression. It's already giving
me a 50-60% compression ratio, and squeezing out more with JPG starts
generating visible artifacts, so it's fine that way.
I think :-)
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