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List:       gimp-user
Subject:    Re: [Gimp-user] removing originak paper texture from high res b&w scans
From:       Steve Kinney <admin () pilobilus ! net>
Date:       2017-04-20 21:57:42
Message-ID: 5eb1b179-0443-c766-6003-3c4aa8775b1b () pilobilus ! net
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On 04/19/2017 02:17 PM, ordinarydream wrote:
> Hello,
> 
> A) SHORT FORM QUERY:
> 
> How to eliminate paper texture and pencil marks, but maintain the almost black
> to completely black ink from drawing scans?
> 
> B) LONG FORM QUERY:
> 
> I have some scans of drawings that I want to print on mildly textured archival
> quality paper. The problem is that the scans retain the texture from the
> original paper that the scan comes from. The consequence of this is that when
> printed on similar paper as the original drawing there is a doubling of textures

I happened to have some scans of art that I am working on myself -
tracing with Inkscape - and when I started playing with the problem of
removing texture I hit on a method that might be worth trying:

1)  Open your image in the GIMP, save as XCF with new name.

2)  Make a duplicate of your base layer (original image), and set its
mode to Overlay.

3)  In the layers dialog, right click the top layer and select "New
layer from visible."  Set this new layer to Overlay as well.

4)  Look at your results, with attention to the unwanted parts only:  If
they are gone (or "gone enough") all is well.

5)  Do "New layer from visible" again, leave its mode set to normal.

6)  Open the Colors > Curves tool, and pull the curve down as far as you
can, without bringing back any of the unwanted texture, faint markings,
etc. from your original scan.  Play with it a bit for best result.  You
are looking to make the "keeper" content of your image as dark as
possible without bringing out significant unwanted details.

7)  Now the trick:  Copy your newest, color curve adjusted layer with
Control+C.  Select your original base layer, and add a new white layer
above it.  Add a layer mask to this new layer.  Left click the mask to
assure it is "current" and do Control-V to paste in your curves adjusted
layer, and left click the arrow icon to merge it down into the layer mask.

8)  Turn off visibility of all layers above the white one with mask, and
check the result:  Ideally, you should see all the inked parts of your
scan, but none of the paper or fainter markings.

Lots of variations on this technique are possible; I found this one with
a minute or so of tinkering.  It works very well on the scan I tested it
out on; your mileage may vary but hopefully not by so much that "one
more tweak" won't provide your desired results.

That one more tweak might include doing "New layer from visible" one
more time, and applying adjustments to that, to alter the appearance of
the inked parts of your scan.

:o)

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