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* [COFF] converting lousy scans of pdfs into something more useable
@ 2023-02-03 15:27 Will Senn
  2023-02-03 16:00 ` [COFF] " Dennis Boone
                   ` (2 more replies)
  0 siblings, 3 replies; 7+ messages in thread
From: Will Senn @ 2023-02-03 15:27 UTC (permalink / raw)
  To: coff

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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:

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 

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?



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^ permalink raw reply	[flat|nested] 7+ messages in thread
[parent not found: <>]
* [COFF] Re: converting lousy scans of pdfs into something more useable
@ 2023-02-03 17:09 Bakul Shah
  0 siblings, 0 replies; 7+ messages in thread
From: Bakul Shah @ 2023-02-03 17:09 UTC (permalink / raw)
  To: Will Senn; +Cc: coff

On Feb 3, 2023, at 8:26 AM, Will Senn <> wrote:
> I can't seem to get away from having to highlight and mark up the stuff I read. I love pdf's searchability of words, but not for quickly locating a section, or just browsing and studying them. I can flip pages much faster with paper than an ebook it seems :).

You can annotate, highlight and markup pdfs. There are apps for that though
I’m not very familiar with them as I don’t markup even paper copies. On an
iPad you can easily annotate pdfs with an apple pencil. 

^ permalink raw reply	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2023-02-04  7:59 UTC | newest]

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-- links below jump to the message on this page --
2023-02-03 15:27 [COFF] converting lousy scans of pdfs into something more useable 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
     [not found] <>
2023-02-03 16:21 ` [COFF] Re: converting lousy scans of pdfs into something more, useable Will Senn
2023-02-03 17:09 [COFF] Re: converting lousy scans of pdfs into something more useable Bakul Shah

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