Hi there,
I've added another new filter in the G'MIC plug-in for GIMP (requires 1.5.6.0+), located in Colors / Colorize comics.

It is intended to ease the colorization of B&W sketch or comics, by trying to extrapolate user-defined color strokes the best it can, i.e. by following the geometry of the original B&W image.
I've done a self-explanatory image that describes the whole process :



The original sketch image has been taken from René van Belzen on Flickr (http://www.flickr.com/photos/aaipodpics/4897590498). The image is licensed under a CC-by-nc-sa creative commons license.

Note that when dealing with multiple layers for comics, a good idea is to consider them in the 'multiply' blending mode.

The idea for this filter has been given to me by David Revoy (http://www.davidrevoy.com/), a very talented illustrator whom you probably already know. David made me discover the 'Lazy Brush' plug-in for TVPaint that does this kind of things (http://lazy-brush.com/), but for $59.
So, I hope that with the G'MIC Colorize comics filter, maybe some of you will save some money (and if you don't know what to do with it, there is a Donation button on the G'MIC web page )

So, you should be able to use it right now. Just refresh your filters. If you have some interesting results to share, just let me know.

EDIT : Interested people may want to see the G'MIC source code I wrote for this effect. As you can imagine, this took me hours of intense effort http://pastebin.com/tYFS28yB

Hi Ronounours,

My version is still 1.5.4.0 because it does not like to be too constantly updating programs. And very recently had upgraded the GMIC.

My question is about what would be the difference between Colorize Comics and Recolorize? Both the G'MIC on Colors.

Most grateful for this tool!

The difference is that 'Colorize comics' is focused on comics
'Recolorize' will spread only the chrominance informations from the color strokes you put on the top layers (so keeping the luminance of the photograph behind unchanged), while 'Colorize comics' will spread all the color informations on the image. It doesn't try to preserve the luminance information of the underlying sketch. That makes a huge difference.
Also, the priority map used to spread the colors is different. For 'Colorize comics' it is computed regarding the fact that you are using a sketch like image. It won't work with regular photographs.

Oh, grateful for the explanation!
I will try!

Wow!

Had to give, and the first experience with this plugin was very satisfying!
Actually presents quite different results from Recolorize, with a much better application for comics!

Sensational!

Thx Ronounours

Thanks David, very good example Akros.

A search for coloring pages in Bing brought me this picture of Tweety.

Definitely's an inker's nirvana. Been following the thread at Flickr by the way. Cool stuff for sure.

I had the chance of having a talented (French) illustrator, Timothée Giet (http://www.timotheegiet.com/) as a tester for this filter, and this is what he got. I must confess I'm very excited to see illustrators trying to do something with this filter for real work. he made my day

This is really a nice plug in.

It does seem to have some small issues or Im not exactly groking it.

Test 1. Complicated Image - Full lineart exported as PNG out of Inkscape. In GIMP I added a white layer below the line art and then a transparent layer above the line art one which I placed my color strokes. Ran the GMIC filter with default settings. The result was definitely not what I was expecting. Colors strayed from the line art and looked more like an abstract piece than a comic. I dont think the filter likes open ends on lineart

Test 2. Simple image. Lineart exported once again as PNG from Inkscape. This time much simpler. Roundish head. Basic mouth, nose eyes and one ear. As this was an Inkscape SVG I know the head shape is closed. Same Gimp Layer set up as in Test 1. On the color stroke layer I used only 2 colors + white. Pink skin. Dark red for tongue. White for teeth. Ran GMIC. Everything worked perfectly this time except for the skin tone. Instead of staying within the head lineart it filled the entire layer.

Any Idea if Im doing something to cause these oddities or if this is the plugin?

Could you provide .xcf files so we can test and check what is going wrong ?
Usually, this is also a good idea not to forget to put 'white' color strokes for the background, otherwise, colors inside characters will extrapolate to the background too.

Also, note that the contours can be opened, the filter will probably work anyway (look at the latest example, near the brush for instance).

I really like how that purple/pink bow gradient worked out.Very nice.

Can I just say wow, like in REALLY AWESOME!!!

Bet you never knew how far your gem would go when you first conceived of it did you David. lol

I bet you there will be a heck of a lot of GIMP converts too because of G'MIC and I do hope the developers keep that in mind before they hose G'MIC support.