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 Post subject: Removing original paper texture from high res b&w scans
PostPosted: Wed Apr 19, 2017 2:17 pm  (#1) 
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GIMP Version: 2.8.14
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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 – the printing paper and the pattern of the paper from the original scan. This leaves an undesirable, and rather fake looking, doubled texture effect in the blank 'white' areas of the images.

An added two-fold complication is that: 1) The ´black´inked areas of the images are not trully uniformly black due to the colour of the ink, erasing, slight errors and the original paper texture. I would, however, prefer that this subtle, uneven inking is maintained, as it preserves the handdrawn look of prints, but; 2) in the scans there is also the appearance of pencil ghosting that is barely visible in the original drawings. I do not want these pencil marks to be visible.
Any simple cutting technique will not do the job as some of the drawings are pointillist, and this cutting would need thousands of repetitions. Additionally, any simple single colour selection technique would not suffice as it is not only pure black, but also dark colours close to black that I need to retain.

So, overall, I basically want to maintain the original ink data, but eliminate the paper texture and the pencil data.

I have been experimenting with a number of different tools, such as the bucket fill plus custom pattern, color select, etc, but I am starting to become overwhelmed with the number of options.

Any pointers appreciated!


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 Post subject: Re: Removing original paper texture from high res b&w scans
PostPosted: Wed Apr 19, 2017 3:09 pm  (#2) 
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Attachment:
TextureRemovalByCurves.png
TextureRemovalByCurves.png [ 139.19 KiB | Viewed 361 times ]

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 Post subject: Re: Removing original paper texture from high res b&w scans
PostPosted: Thu Apr 20, 2017 10:53 am  (#3) 
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Hey wow!

:kpix Super clear and efficient reply. Having some clear sense of direction is a great help in the sea of potential options that technology provides. Feeling positive right now.

Will go now and work those curves into streamlined images!

Thanks,

Luke


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 Post subject: Re: Removing original paper texture from high res b&w scans
PostPosted: Thu Apr 20, 2017 11:07 am  (#4) 
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Thanks Ofnuts! That's a function of the color curve I never even thought of! This will help me with some images as well!

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 Post subject: Re: Removing original paper texture from high res b&w scans
PostPosted: Thu Apr 20, 2017 2:02 pm  (#5) 
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Yup it´s super simple, and from my preliminary observations, it seems to almost entirely clean up the picture. Only what appears to be some very light diagonal lines, a few scratches and extra dark marks remain.


Last edited by ordream on Thu Apr 20, 2017 4:03 pm, edited 1 time in total.

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 Post subject: Re: Removing original paper texture from high res b&w scans
PostPosted: Thu Apr 20, 2017 2:46 pm  (#6) 
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I (think I) can also recommend using Colors->Threshold to find out, just where, along the spectrum of dark-to-light the artifacts lie. (Don't have to save the Threshold operation, only use it for info.)

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 Post subject: Re: Removing original paper texture from high res b&w scans
PostPosted: Fri Apr 21, 2017 2:37 pm  (#7) 
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Hey Gramp,

When I try the Colours -> Threshold some strange things seem to appear. I can't quite see the point where the paper texture artefacts emerge. Instead, Threshods seems to destroy the paper texture, but it also seems to degrade the ink, in a most curious way: where there is an additional retouching with the pen or heavy application of ink (not visible to the eye) this is retained - like one of those x-rays in art restoration or forger videos . This is an interesting effect and it seems like a good trick for a would be art restorer, but the Curves seems to be the easiest and most effective so far.


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 Post subject: Re: Removing original paper texture from high res b&w scans
PostPosted: Sat Apr 22, 2017 1:35 pm  (#8) 
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ofnuts wrote:
Attachment:
TextureRemovalByCurves.png

Thanks for the tip, Ofnuts.

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