From: Will Senn <will.senn@gmail.com>
To: coff@tuhs.org
Subject: [COFF] Re: converting lousy scans of pdfs into something more, useable
Date: Fri, 3 Feb 2023 10:21:31 -0600 [thread overview]
Message-ID: <c833ee65-a335-6d19-ffc5-18954f105bcb@gmail.com> (raw)
In-Reply-To: <167544017712.2485736.11108085155717490044@minnie.tuhs.org>
> From: Dennis Boone <drb@msu.edu>
>
> * Don't use JPEG 2000 and similar compression algorithms that try to
> re-use blocks of pixels from elsewhere in the document -- too many
> errors, and they're errors of the sort that can be critical. Even if
> the replacements use the correct code point, they're distracting as
> hell in a different font, size, etc.
I wondered about why certain images were the way they were, this
probably explains a lot.
> * OCR-under is good. I use `ocrmypdf`, which uses the Tesseract engine.
Thanks for the tips.
> * Bookmarks for pages / table of contents entries / etc are mandatory.
> Very few things make a scanned-doc PDF less useful than not being able
> to skip directly to a document indicated page.
I wish. This is a tough one. I generally sacrifice ditching the
bookmarks to make a better pdf. I need to look into extracting bookmarks
and if they can be re-added without getting all wonky.
> * I like to see at least 300 dpi.
Yes, me too, but I've found that this often results in too big (when
fixing existing), if I'm creating, they're fine.
> * Don't scan in color mode if the source material isn't color. Grey
> scale or even "line art" works fine in most cases. Using one pixel
> means you can use G4 compression for colorless pages.
Amen :).
>
> * Do reduce the color depth of pages that do contain color if you can.
> The resulting PDF can contain a mix of image types. I've worked with
> documents that did use color where four or eight colors were enough,
> and the whole document could be mapped to them. With care, you _can_
> force the scans down to two or three bits per pixel.
> * Do insert sensible metadata.
>
> * Do try to square up the inevitably crooked scans, clean up major
> floobydust and whatever crud around the edges isn't part of the paper,
> etc. Besides making the result more readable, it'll help the OCR. I
> never have any luck with automated page orientation tooling for some
> reason, so end up just doing this with Gimp.
Great points. Thanks.
-will
next parent reply other threads:[~2023-02-03 16:23 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <167544017712.2485736.11108085155717490044@minnie.tuhs.org>
2023-02-03 16:21 ` Will Senn [this message]
2023-02-03 17:09 [COFF] Re: converting lousy scans of pdfs into something more useable Bakul Shah
-- strict thread matches above, loose matches on Subject: below --
2023-02-03 15:27 [COFF] " Will Senn
2023-02-03 16:00 ` [COFF] " Dennis Boone
2023-02-03 16:01 ` Bakul Shah
2023-02-03 16:25 ` Will Senn
2023-02-04 7:59 ` Ralph Corderoy
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=c833ee65-a335-6d19-ffc5-18954f105bcb@gmail.com \
--to=will.senn@gmail.com \
--cc=coff@tuhs.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).