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Correcting color in AGED documents

Sep 2, 2012, 19:07
Post: #1
Correcting color in AGED documents
I have some letters - written in 1860 (yes, civil war era) and have been scanning them for my web site.
Some of these letters are so badly aged that the paper has turned tan/brown and the text, often in pencil, is very difficult to read.
Attached, I hope, is a sample of what I'm working with. Some are better, many are worse.
Since I'm new to GIMP (and photo editing in general) can some kind soul suggest how to lighten up the background / enhance the writing so I can present these as legible??
I'd point you to my web site, but I'm in the middle of making changes and it's thoroughly screwed at the moment.
Thanks //al


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Sep 2, 2012, 20:00
Post: #2
RE: Correcting color in AGED documents
A possible solution:

- Duplicate the layer
- Select the top layer and use Filter/Blur/Gaussian/Blur with large radius (the text must completely disappear). I used 200pixels.
- Using the mode selector at the top of the Layers list, put the top layer in "Grain extract" mode.
- This will both even out the lighting and make the paper a neutral gray
- Do "Layer/New from visible" to create a layer with the fixed image
- Select that layer
- You can use "Colors/Brightness contrast" to add a bit of contrast
- You can also use "Filters/Enhance/Unsharp mask" to make the writing a bit sharper (I used radius=3, amount=1)

[attachment=1421]

If my explanation doesn't make too much sense, Google the terms, or ask here for more detail.

Note down the settings you use (blur radius, contrast value, unsharp mask settings). You can later envision to process all your images automatically by using these settings with a batch processing tool.

Save your image as XCF, which saves all the layers. This may be useful if you want to try other things later. In Gimp 2.8, you can use "File/Export" to additionally save the file with a generic file type to use elsewhere (Web page, etc...).

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Sep 2, 2012, 20:04
Post: #3
RE: Correcting color in AGED documents
PS: if you scan the other side it may be possible to subtract each side from the other to remove the see-through writing. Post the image of the other side if you want me to try things for this.

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Sep 2, 2012, 20:28
Post: #4
RE: Correcting color in AGED documents
Google are my friend Smile Let me see what sense I can make of your first comment first.
Thanks //al
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Sep 2, 2012, 21:07
Post: #5
RE: Correcting color in AGED documents
PPS: instead of using the Contrast tool, you have better use the "Levels" tools to stretch the dynamic of the image (make the white very white and the black very black). In the sample below: 67 for the blacks, 167 for the whites, and 2.0 for the middle.

[attachment=1422]

The image you sent is also suffering from too much JPEG compression. If this is what you got from the scanner you have to increase the quality. There is also a moiré pattern with the grain of the paper.

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Sep 3, 2012, 14:42
Post: #6
RE: Correcting color in AGED documents
Okay, I think I figured out what you said in the first message and have gotten a decent image from another letter, thanks much for that.
The image I posted is not what's coming from the scan, it's a thumbnail that I have on web with a transcription of the letter. My scans, taken at 600x600 come out to well over a couple of meg and didn't figure it would be polite to inflict one of those on you.
Working from a new scan and taking the contrast very high actually gave me a good (in my view) image - one that I wouldn't mind posting. Now I'll go take a look at your expansion and see what I can do there.
I'm a retired programmer turned truck driver (mid-life crisis, what can I say I was bored!) and neither web work nor graphics have been any part of the work I've been doing so I really appreciate your excellent help.
//al
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Jun 16, 2014, 16:37 (This post was last modified: Jun 16, 2014 16:38 by aljones.)
Post: #7
RE: Correcting color in AGED documents
Okay, back for some more help. The above has been working well for most of the letters I have, but the backgrounds on most of them is tan (faded white paper). I have another one that is green ... and I can't resolve it to anything readable,

Too large a file to attach, it can be found at http://aljones.us/images/600312ln3.JPG

This one is almost readable as is, the black is good; 600312ln1.jpg is not so good. Any help here?? (watch the case on the extension, I have a linux host)
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Jun 16, 2014, 22:04
Post: #8
RE: Correcting color in AGED documents
Some success with sharpen by synthesis (2.0)(*) followed by the blur/grain extract maneuver above:

[attachment=3644]

(*) requires the resynthesizer plugin (on ubuntu, part of the gimp-plugin-registry package)

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