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I hope this is the right forum to ask this.

I've got some old documents (part of a drawing) that I want to scan, but the original documents are quite old and the color has degraded (although the paper itself is in relatively good shape). See examples (fairly readable, and really difficult to make out):

relatively clean part

Blown up region of heavily

What I would like to know is :

  1. what type of filters (preferably available in GIMP) would you explore to clean up this type of noise. My main aim is to make the text readable.
  2. Get at least the name of this type of noise in the documents (english is not my native language), so I can research it further myself online.

I suspect there are many steps that need to be followed before you can process this, so I would appreciate it you could outline a possible algorithm, (e.g. 1. convert to grayscale, 2. threshold etc)

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    \$\begingroup\$ a couple of questions... 1. will you be okay if I explained it in Photoshop and then you can use something similar in Gimp. 2. have you tried a Smartphone App call Adobe Scan? it has a feature when scanning a document with the flash light on to only bring out the text. it can cancel out creases and discoloration \$\endgroup\$ Commented Nov 28, 2020 at 14:23
  • \$\begingroup\$ GIMP was a preference, not a requrement. Regarding Adobe scan, I have not used it but I'll try. \$\endgroup\$
    – NMech
    Commented Nov 28, 2020 at 15:02
  • \$\begingroup\$ Adobe Scan really does an amazing job at least for the top image. The only drawback (for me) is that you need to register. The bottom image wasn't as great but maybe with better lighting that will change. \$\endgroup\$
    – NMech
    Commented Nov 29, 2020 at 7:27

1 Answer 1

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The quickest way I have found to do this is via Luminosity Masks.

  1. First REMOVE COLOUR from the image.

  2. INCREASE BLACKS

  3. SPOT HEAL dark areas of image not Required.

  4. Create a CURVE Adjustment Layer

  5. Select COLOUR RANGE

  6. Adjust the curve to fade away the colour range.

  7. Make multiple passes with New Curve Adjusments for each new Tone.

  8. Do this until you're left with just the dark Tones.

  9. Create a SOLID WHITE LAYER

  10. Select COLOUR RANGE and colour pick the chart

  11. Create a NEW Layer with this Selection and drag it over the White Layer

  12. Finally, just do spot healing to tidy up.

The process took me just under 5 minutes and below is what I am left with.

Please don't forget, I have just rushed through it and with more time and effort, you should be able to get a better result

enter image description here

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  • \$\begingroup\$ if you ever decide on making a youtube channel, with sort of thing, please update this question so that I can follow :-) Right now, I am trying to replicate what you did on GIMP, but I am nowhere near as proficient as you. Do you by any chance, have a name for this type of discoloration of documents? \$\endgroup\$
    – NMech
    Commented Nov 29, 2020 at 7:30
  • \$\begingroup\$ How far did you manage on GIMP? Unfortunately, I don't have a Youtube channel but if I ever do, I will include this. I have never used GIMP and never even seen it before, but what I will do is install GIMP on my laptop and try to learn it. maybe then I can be more help. \$\endgroup\$ Commented Nov 29, 2020 at 18:11
  • \$\begingroup\$ This technique produces similar results to a high-pass filter (also similar to edge detection). Great answer, great explanation of steps required. \$\endgroup\$
    – scottbb
    Commented Nov 30, 2020 at 1:49

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