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Remove color pencil from b/w illustration

Jul 20, 2011, 05:40
Post: #1
Remove color pencil from b/w illustration
I have a bunch of images that look like

[Image: pic011v.jpg]

and I want to 'restore' them like

[Image: pic011fix.jpg]

Unfortunately that took an inordinate amount of pixel-fiddling to do and I have over 80 more of them.

Even more unfortunately, that was an 'easy' image compared to some of the others:

[Image: pic008q.jpg]

[Image: pic027q.jpg]

Another easier one

[Image: pic024.jpg]


I know basically nothing about image processing and my current workflow looks like:
irfanview: convert to grayscale
ms photo editor: adjust contrast
ms paint (please don't laugh too hard): clean-up what's left

Obviously this is inadequate for the task and I was wondering if Gimp could help out.

Any help or suggestions would be greatly appreciated.



Source images if you're interested . . .
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Jul 20, 2011, 12:56
Post: #2
RE: Remove color pencil from b/w illustration
Always good to use the basic tools, so that you know what they do.
In this case you might have an all-in-one solution if you get the gmic plugin from

http://gmic.sourceforge.net/

One of the filters is "B&W recolorize"

Set the second colour to black (default is a very dark blue)
Set the third and fourth colours to white.

something like this

http://i.imgur.com/7okT5.jpg

then ok it.

** https://www.gimp-forum.net/ now answering questions**
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Jul 20, 2011, 22:53 (This post was last modified: Jul 20, 2011 22:58 by lontarm.)
Post: #3
RE: Remove color pencil from b/w illustration
(Jul 20, 2011 12:56)rich2005 Wrote:  In this case you might have an all-in-one solution if you get the gmic plugin from

Thanks, that truly does an amazing job!

But . . .

it seems to make the whole image b/w with no grayscale which really hurts the quality.

Old way

[Image: pic011fix.jpg]

New way (with gmic)

[Image: pic011bw.jpg]

Is there any way to keep the grayscale or 'soften' it or something?



(Jul 20, 2011 06:59)ofnuts Wrote:  Image obtained with the layer mask technique.

Thanks for the tip!

I haven't tried this so I can't be sure, but it looks like it wiped out a lot of detail and has the same problem in that it makes the image b/w with no grayscale.
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Jul 20, 2011, 23:37 (This post was last modified: Jul 20, 2011 23:37 by lontarm.)
Post: #4
RE: Remove color pencil from b/w illustration
(Jul 20, 2011 23:14)ofnuts Wrote:  There is no grayscale in a line art?

Maybe I'm talking about the aliasing so the lines aren't so jaggy?

I don't know what I'm talking about, I just know it looks different if I turn the contrast all the way up (and not in a good way)

(Jul 20, 2011 23:14)ofnuts Wrote:  Another shot at the layer mask technique on the fullsize image, but:

1) I used contrast & brightness instead of threshold
2) I didn't push the cursors too far, and cheated: the remaining colors have just been desaturated.
3) on the result image, I played with the contrast and the opacity of the line art

Wow! That looks impressive.

I'm off to see if I can duplicate that . . .
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Jul 21, 2011, 07:40
Post: #5
RE: Remove color pencil from b/w illustration
The great thing about gimp is "there is always another way...."

In this case and again using the gmic plugin, maybe adjust the second colour to a dark-ish grey. Its worth playing around with the levels and colours since you get a reasonable preview and it is quick.

as http://i.imgur.com/Ukbxw.jpg I can't see the difference between the original and the 'fix' but then your eyes will be better than mine.

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Jul 21, 2011, 19:04
Post: #6
RE: Remove color pencil from b/w illustration
(Jul 21, 2011 07:40)rich2005 Wrote:  The great thing about gimp is "there is always another way...."

In this case and again using the gmic plugin, maybe adjust the second colour to a dark-ish grey. Its worth playing around with the levels and colours since you get a reasonable preview and it is quick.

Still lots of cleanup on some of the more difficult images, but seems to work the best of anything so far, thanks!
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Jul 21, 2011, 21:36
Post: #7
RE: Remove color pencil from b/w illustration
How do you apply a plugin or filter to only a specified part of the image?
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Jul 22, 2011, 07:28
Post: #8
RE: Remove color pencil from b/w illustration
@ lontarm

I made a little video on making selections, going through the tools that Gimp has. Only about making a selection, not what to do with it afterwards, which in Gimp can be many and varied.

Might be useful for a beginner. About 11 minutes.

http://www.youtube.com/watch?v=aUHEI-bVSPo

One thing that you should get in the way of, is saving in Gimp .xcf format. It will save your layers, paths, selections for the next time you come to edit. When you are finished you can save in a more compact format, png or jpeg.

** https://www.gimp-forum.net/ now answering questions**
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Jul 23, 2011, 01:34
Post: #9
RE: Remove color pencil from b/w illustration
(Jul 21, 2011 21:48)ofnuts Wrote:  It would be better IMHO to duplicate the layers, apply different corrections to them to optimize different parts of the images (you can take advantage of the different colors), and then merge the results, by applying transparency at the right places (layer masks with a gradient for instance)

It looks like English, but . . . Huh

(Jul 22, 2011 07:28)rich2005 Wrote:  http://www.youtube.com/watch?v=aUHEI-bVSPo

Watched it, thanks.

But it is las-so not las-sue Tongue
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Jul 23, 2011, 05:12
Post: #10
RE: Remove color pencil from b/w illustration
So I duplicated the layers and did different things to different layers and now I want to combine the layers.

As ofnuts suggested I'm trying to use layer masks and transparency, but lets just say I'm not getting very far. Does anyone have some good tutorials on that?
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Jul 23, 2011, 06:54
Post: #11
RE: Remove color pencil from b/w illustration
Well I am making some (painful) progress but at least I think I have some of the basics down. Hopefully I'll have more intelligent questions tomorrow.
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Jul 25, 2011, 16:25
Post: #12
RE: Remove color pencil from b/w illustration
Thanks ofnuts.

Now I'm having an issue with the bucket tool.

When manually cleaning, I fill with red to better catch areas that need fixing, but when I fill back with white or use color exchange to go from red to white, it leaves a sprinkling of red all over the place.
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Jul 25, 2011, 18:09 (This post was last modified: Jul 25, 2011 18:10 by lontarm.)
Post: #13
RE: Remove color pencil from b/w illustration
(Jul 25, 2011 17:42)ofnuts Wrote:  you can set a threshold to tell it what to consider similar colors.

Ok so I'm somewhat confused by this. Whatever criteria it uses to decide whether to color an area shouldn't matter. Once it's colored, it's red (right?). And when I change red to white, why would there be any red left over since it should all be the same red?

I guess I'm just used to the superior way Paint works Big Grin

(Jul 25, 2011 17:42)ofnuts Wrote:  Considering that there is nothing of importance in your drawing, you should be able to use the curves or levels tools to transform everything above some value (around 200, I would say) into pure white.

I guess I really don't understand those tools. No matter how I drag around the curve or the little triangles, the red areas stay red (unless they turn black). (I do set the channel to red right?)
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Jul 25, 2011, 20:22
Post: #14
RE: Remove color pencil from b/w illustration
http://hotfile.com/dl/125001066/44ffe68/...f.bz2.html

I put the before / after red fill / after white fill as separate layers.
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Jul 26, 2011, 00:33 (This post was last modified: Jul 26, 2011 00:35 by lontarm.)
Post: #15
RE: Remove color pencil from b/w illustration
(Jul 25, 2011 23:39)ofnuts Wrote:  filling with red and then with white does nothing to clear up things.

Just to be clear, I'm not expecting the fills by themselves to clear anything up, I just expect the one fill to 'undo' / invert the previous fill.

In Paint if you fill with one color and then fill with the original color you get back to exactly where you started (in most cases).

(Jul 25, 2011 23:39)ofnuts Wrote:  "White" isn't a color and it doesn't behave exactly like the others for fills.

That's not the (complete) issue because I can fill the red with green (instead of white) and I still have those same red spots left over.

edit: oh, unless you're talking about white/gray in the pixels and not the fill color itself . . .

(Jul 25, 2011 23:39)ofnuts Wrote:  If you are searching for spots, try the technique I show in this thread:
http://gimpforums.com/thread-colour-to-a...ite-pixels (post dated Jul 20, 2011, 22:31)

Ok, will give this a try
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