On Saturday, 29 January 2022, at 11:14 PM, Bakul Shah wrote:
> Note that djvu would compress things very nicely. A full page
300dpi magazine color page that may be 25MB uncompressed will
compress down to 40K-80K or so and be very legible, much more
so compared a similar sized jpeg compressed image.

Thanks for your hint. I'm using djvu format for scanned book pages for my private use. The algorithm isn't easy to reimplement cause it uses pattern matching in an extensive way. You get the best results for scanned material where as an example letters are matched quite often. It has superb compression ratios but is slow regarding decompression or rendering.

Regarding handwritten scans the best method I experienced is edge detection filtering and color indexing to create a ppm image. Compression leads than to smaller sizes than by using jpeg. Decompression is faster and when you combine two lines to single one (subpixeling) you get smooth and clean images.

For printed sources djvu produces far smaller results. Thank you for this hint.

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