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How do you encode your paper scans? (lemmy.ml)
submitted 3 years ago by to c/selfhosted@lemmy.world
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I assume many of you host a DMS such as Paperless and use it to organise the dead trees you still receive in the snail mail for some reason in the year of the lord 2023.

How do you encode your scans? JPEG is pretty meh for text even at better quantisation levels ("dirty" artefacts everywhere) and PNGs are quite large. More modern formats don't go into a PDF, which means multiple pages aren't possible (at least not in Paperless).

Discussion on GH: https://github.com/paperless-ngx/paperless-ngx/discussions/3756

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[–] [S] 1 point 3 years ago* (1 child)

Using an OK scanner makes a big difference.

WDYM? The lossless scans SANE produces themselves subjectively look very good. My only issue is the transcoding to lossy formats I want to do in order to save >3/4 of the space.

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  • [–] 1 point 3 years ago (2 children)

    Oh, it's common in my country to use a smartphone to 'scan' documents by actually just taking a lousy photo of them. It's so prevalent that when you tell someone to do a scan they usually do this instead.

    I bought a cheap canon scanner for 50$ and it's pretty perfect for legal documents. A little slow maybe. I use SANE, then do lossy compression too.

    In rare situations I'd then post process the PDF to even worse quality using ghostscript, for example when a foreign visa application form requires a scan of a really long document, but doesn't accept sizes over 2MB.

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  • [–] [S] 1 point 3 years ago (2 children)

    I use SANE, then do lossy compression too.

    Well, what kind of lossy compression? JPEG?

    IME, JPEG looks quite terrible for text documents -even at q=95.

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  • [–] 1 point 3 years ago (1 child)

    @Atemu
    I just use grayscale PNGs, myself. optipng usually takes them down to a decent size.
    @Saigonauticon

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  • [–] [S] 1 point 3 years ago (2 children)

    Hmm, I'm using grayscale PNGs as my baseline here. A 150dpi scan is about 1.3MiB.

    A (for the purpose of text documents) similar quality WEBP is about 1/4 of that.

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  • [–] 1 point 3 years ago

    You could also try adjusting the contrast a bit. I use an app called Genius Scan, which increases the contrast of the scanned image to reduce the number of bits needed per pixel. This reduces the size of the file quite a bit, although it obviously isn't a true representation of the scanned document. The TextCleaner imagemagick plugin looks like it's doing something similar.

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  • [–] -1 points 3 years ago (1 child)

    @Atemu
    Webp is much better, as long as your target reader(s) support it.

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  • [–] [S] 1 point 3 years ago (1 child)

    Yes, as I said.

    As also mentioned in the post, I need a solution for multiple pages and an image (no matter what format) only represents a single page and WEBPs don't go into PDFs.

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  • [–] 0 points 3 years ago (1 child)

    @Atemu
    There's not really a magic bullet here. The current answer is to prepare a PDF outside of paperless and feed it in: https://github.com/paperless-ngx/paperless-ngx/discussions/367

    mpflanzer on that Issue is working on a file merging feature, but it's not ready yet.

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  • [–] [S] 1 point 3 years ago

    That's nice and all but does not answer how you'd create the PDF. Whether that happens outside paperless inside paperless does not make a difference. In the end, I need to create a PDF/A out of some images and the question on how to encode these images still remains.

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