3 Feb
2023
3 Feb
'23
3:27 p.m.
All,
I thought I would post something here that wasn't DOA over on tuhs and
see if it would fly here instead. I have been treating coff as the
destination for the place where off-topic tuhs posts go to die, but
after the latest thread bemoaning a place to go for topics tangential to
unix, I thought I'd actually start a coff thread! Here goes...
I read a tremendous number of documents from the web, or at least read
parts of them - to the tune of maybe 50 or so a week. It is appalling to
me in this era that we can't get better at scanning. Be that as it may,
the needle doesn't seem to have moved appreciably in the last decade or
so and it's a little sad. Sure, if folks print to pdf, it's great. But,
if they scan a doc, not so great, even today.
Rather than worry about the scanning aspects, I am more interested in
what to do with those scans. Can they be handled in such a way as to
give them new life? Unlike the scanning side of things, I have found
quite a bit of movement in the area of being able to work with the pdfs
and I'd really like to get way better at it. If I get a bad scanned pdf,
if I can make it legible on screen, legible on print, and searchable,
I'm golden. Sadly, that's way harder than it sounds, or, in my opinion,
than it should be.
I recently put together a workflow that is tenable, if time consuming.
If your interested in the details, I've shared them:
https://decuser.github.io/pdfs/2023/02/01/pdf-cleanup-workflow.html
In the note, I leverage a lot of great tools that have significantly
improved over the years to the point where they do a great job at what
they do. But, there's lots of room for improvement. Particularly in the
area of image tweaking around color and highlights and such.
The note is mac-centric in that I use a mac, otherwise, all of the tools
work on modern *nix and with a little abstract thought, windows too.
In my world, here's what happens:
* find a really interesting topic and along the way, collect pdfs to read
* open the pdf and find it salient, but not so readable, with sad
printability, and no or broken OCR
* I begin the process of making the pdf better with the aforementioned
goals aforethought
The process in a nutshell:
1. Extract the images to individual tiffs (so many tools can't work with
multi-image tiffs)
* pdfimages from poppler works great for this
2. Adjust the color (it seems impossible to do this without a batch
capable gui app)
* I use Photoscape X for this - just click batch and make
adjustments to all of the images using the same settings
3. Resize the images - most pdfs have super wonky sizes
* I use convert from imagemagick for this and I compress the tiffs
while I'm converting them
4. Recombine the images into a multi-tiff image
* I use tiffcp from libtiff for this
5. OCR the reworked image set
* I use tesseract for this - It's gotten so much better it's ridiculous
This process results in a pdf that meets the objectives.
It's not horribly difficult to do and it's not horribly time consuming.
It represents many, many attempts to figure out this thorny problem.
I'd really like to get away from needing Photoscape X, though. Then I
could entirely automate the workflow in bash...
The problem is that the image adjustments are the most critical - image
extraction, resize, compression, recombining images, ocr (I still can't
believe it), and outputting a pdf are now taken care of by command line
tools that work well.
I wouldn't mind using a gui to figure out some color setting (Grayscale,
Black and White, or Color) and increase/decrease values for shadows and
highlights if those could then be mapped to command line arguments of a
tool that could apply them, though. Cuz, then the workflow could be,
extract a good representative page as image, open it, figure out the
color settings, and then use those settings with toolY as part of the
scripted workflow.
Here are the objectives for easy reference:
1. The PDF needs to be readable on a decent monitor (zooming in doesn't
distort the readability, pixelation that is systematic is ok, but not
preferred). Yes, I know it's got a degree of subjectivity, but blobby,
bleeding text is out of scope!
2. The PDF needs to print with a minimum of artifact (weird shadows,
bleeding and blob are out). It needs to be easy to read.
3. The PDF needs to be searchable with good accuracy (generally, bad
scans have no ocr, or ocr that doesn't work).
Size is a consideration, but depends greatly on the value of the work.
My own calculus goes like this - if it's modern work, it should be way
under 30mbs. If it's print to pdf, it should be way under 10mb (remember
when you thought you'd never use 10mb of space... for all of your files
and the os). If it is significant and rare, less than 150mbs can work.
Obviously, this is totally subjective, your calculus is probably quite
different.
The reason this isn't posted over in pdf.scans.discussion is that even
if there were such a place, it'd be filled with super technical
gibberish about color depth and the perils of gamma radiation or
somesuch. We, as folks interested in preserving the past have a more
pragmatic need for a workable solution that is attainable to mortals.
So, with that as a bit of background, let me ask what I asked previously
in a different wayon tuhs, here in coff - what's your experience with
using sad pdfs? Do you just live with them as they are, or do you try to
fix them and how, or do you use a workflow and get good results?
Later,
Will