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Removing original paper texture from high res b&w scans
#1
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!


Attached Files
.xcf   paper texture and pencil ghosting example.xcf (Size: 176.88 KB / Downloads: 41)
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#2
Your sample is a bit small but a couple of things to try.

I would put the image into grayscale first: Image -> Mode -> Grayscale

Colors -> Curves and pull the curve up screenshot: http://i.imgur.com/OmexI8i.jpg

There is a Gimp plugin g'mic http://www.gmic.eu which has a filter Repair -> Repair scanned documents which might give a result  screenshot: http://i.imgur.com/o2NGnRD.jpg
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#3
Unless I'm missing something, rather easy with Curves (Curves):

   
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#4
I tend to use the colorpickers in the Levels tool, to set a black and a white point.
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#5
Big Grin Hello respondents!

Thanks soo much - soo fast with responses and the screenshots are easy to understand. Clear communication, free of personal slurs - an enlightening forum experience!

I shall try the curves and then investigate the plugin, however: Please excuse my total ignorance, but the plug in with the scan repair tool is a separate program that interacts with gimp or...?? I don´t even know what a plugin is; in my anachronistic mind plug in is a phrasal verb, not a noun - much to learn have I.......

Thanks heeeaaps

Luke

(04-20-2017, 01:32 AM)Espermaschine Wrote: I tend to use the colorpickers in the Levels tool, to set a black and a white point.

Hiya,

Is that the colour selection tool in the lefthand toolbox? If so I have tried that, but due to ink not being uniformly black the selection is patchy. I guess I can try integrating layers of very similarly selected colours with this method, though?

Thanks,

Luke
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#6
Quote:Please excuse my total ignorance, but the plug in with the scan repair tool is a separate program that interacts with gimp or...?? I don´t even know what a plugin is; in my anachronistic mind plug in is a phrasal verb, not a  noun - much to learn have I.......

Scripts and plugins extend the capabilities of Gimp, in fact Gimp is built around plugins.

The g'mic plugin is unusual in that it comes with an installer. Once installed and with an image open you start it from an entry bottom of the Filters menu.

However, since adjusting the color curve seems to work for you, stick with that and keep the subject of plugins for another time.
A little dated but worth a read: http://libregraphicsworld.org/blog/entry...management
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#7
No, its the Levels Tool Smile

My approach is more or less the same as ofnuts', just with another tool.
The Levels Tool has inbuild colourdroppers you can use to click in the image and define that as the white/black point, depending on which of the two droppers you use.

See here for more information:
https://docs.gimp.org/2.6/en/gimp-tool-levels.html

   
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#8
(04-20-2017, 04:16 PM)Espermaschine Wrote: No, its the Levels Tool Smile

My approach is more or less the same as ofnuts', just with another tool.
The Levels Tool has inbuild colourdroppers you can use to click in the image and define that as the white/black point, depending on which of the two droppers you use.

See here for more information:
https://docs.gimp.org/2.6/en/gimp-tool-levels.html

Yes, but there is nothing you can do with Levels that you can't do with Curves. The benefit of Curves here is that you can easily ensure that nothing happens in the left part of the histogram, which the OP wants to keep unscathed.

Btw in Curves, if you click in the image, it draws a vertical line on the histogram corresponding to the value of the pixel you clicked on.
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#9
Again just ACE!

Extra query:

I have the G´mic plugin and have found the scan repair function. This is all good. What I do want to know, however, is whether the levels of the variables that are automatically selected are those that the magic algorithms have decided are the best or should I still try to tinker?

Thanks,

Luke
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#10
Definitely tinker, a great way to learn Gimp is experiment. Make sure you learn the standard Gimp tools first.
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