removing fold shadow / highlight from a scan

[tommik128]

Hi guys. I am new to GIMP. Today I was trying to balance the background of a scanned audio CD cover that had slightly different color tones (highlighted) on a folded side of a scan. Pretty much something like this issue presented on this scanned page:

http://i.imgur.com/aIU3zCH.jpg

What I used was the Select by color tool and then filled the area with Bucket fill tool with just one of the colours from the rest of the background using Color picker tool to sort of balance the overall background to get rid of that fold.

But I am wondering if you could actually fill the area with a portion of an image itself (something like cloning / healing). I can't see this option in Bucket fill tool. The reason is that I think it might look better being filled with actual scanned pattern rather than one strick colour all over.

Or is there a better way to get rid of fold shadows / highlights?


Thank you very much for your answers.

[rich2005]

For that particular type of scan the method proposed by Ofnuts works very well.

Duplicate the layer
Put the duplicated layer mode to divide
Blur the duplicated layer, 'Filters -> Blur -> Gaussian Blur'
Adjust the x/y values and being a GEGL filter you can see the result as you adjust.

   

Otherwise, the gmic plugin http://www.gmic.eu has a very good 'repair scanned documents filter.

[Ofnuts]

Another technique (better done in Gimp 2.10):

• Duplicate the layer, and set the top layer to Grain extract: the whole image turns a uniform gray.
  
• Filters>Blur>Gaussian blur and blur the top layer. The characters will re-appear in black. Increase the blur until the characters are dark and the halo around them is no longer visible but don't go too far otherwise the fold shadow will reappear.
  

   

• Layer>New from visible and use Levels or Curves to make the grey white, and the black very black
  

   

[The ancient one]

Good day Ofnuts

In this and other threads you say words like
* Duplicate the layer
* Apply a very heavy gaussian blur. The drawing/text should no longer be visible (I use something like 1/5th of the image diagonal)
* Put the top layer in Grain Extract mode.

The problem I have is I cannot find any reference to Grain Extract mode anywhere on this forum and other locations like Vimeo and youtube despite hours searching (the only results I have found are your posts recommending this)
The most helpful thing I found very early on was that typing /grain should produce a dropdown of options. As soon as I get to /grai the options change to zero. I am using 2.10.22 on Win7.

I know the problem must be me so can you please post how to do grain extract in simple words that even a grumpy ancient like me (well past 75) can understand

Thanks

[Krikor]

(01-02-2021, 09:37 PM)The ancient one Wrote: [...]

The problem I have is I cannot find any reference to Grain Extract mode anywhere on this forum and other locations like Vimeo and youtube despite hours searching (the only results I have found are your posts recommending this)
The most helpful thing I found very early on was that typing /grain should produce a dropdown of options. [...]
Thanks

In the windows layers dialog:
   

[The ancient one]

Thank you very much
Now to try this out on some files

[Ofnuts]

Actually I use a better technique now:

• Filters>Enhance>Wavelet decompose
  
• On the Residual channel: "Filter>Blur>Pixelize" and pixelize to its size to average it.
  

You can also at the same time duplicate the top layers to increase sharpness/contrast of text.

[The ancient one]

Thanks - today was a total waste of time. I just could not get my act together
Will try tomorrow if I can find time

[The ancient one]

(01-03-2021, 03:16 AM)Krikor Wrote:

(01-02-2021, 09:37 PM)The ancient one Wrote: [...]

The problem I have is I cannot find any reference to Grain Extract mode anywhere on this forum and other locations like Vimeo and youtube despite hours searching (the only results I have found are your posts recommending this)
The most helpful thing I found very early on was that typing /grain should produce a dropdown of options. [...]
Thanks

In the windows layers dialog:

I hate to admit it but this has got me beat.
 
My layers dialog is exactly the same as in the on line manual chapt 16 Figure 16.104. The Contents of the “Layer” local pop-menu
 
and in my windows dialog the same as in Figure 16.259. Contents of the “Windows” Menu
 
I have right clicked the picture and thumbnail and clicked through all the menus that I can find an I cannot find the menu you posted

This is a whole new ballgame for this ancient one and I do not want it to beat me.

[The ancient one]

(01-03-2021, 09:01 AM)Ofnuts Wrote: Actually I use a better technique now:

• Filters>Enhance>Wavelet decompose
  
• On the Residual channel: "Filter>Blur>Pixelize" and pixelize to its size to average it.
  

You can also at the same time duplicate the top layers to increase sharpness/contrast of text.

I guess I am just too old to grasp some essential as the two dot points produced nothing but a fuzzy mess.  Presumably I am missing some blindingly obvious next step.

I did not do the third step as I wanted to see how it looked before and after