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Currently I'm working on converting 30+ artworks to a colouring book, extracting the lines as best as I can and vectorizing them. Both my gf and I work as graphic designers and neither of us have come up with a solution that gives satisfying results. Of course having to clean-up manually is unavoidable, which is what we have done so far, but perhaps there are some techniques that we overlooked, some time savers. I don't need each and every line, but it does need to be quite detailed also because the artist likes to decide on what to leave out.

Here's an example:enter image description here

And here is an example of one I did before:

enter image description here

Techniques I used: increase contrast and reduce colours in various ways: convert to CMYK then take out CMY, index colours, posterize, adjust levels de-saturate, duplicate as a colour dodge layer (fairly effective) and gimp cartoon effect was also pretty good. Nevertheless after extracting the outline a lot of handywork remained, the example took me 6 hours before I could trace a satisfyingly smooth vector. The artist is very specific about the way his lines should look. He wants to preserve his trademark brush strokes. Unfortunately he doesn't exclusively use black for the outlines, they can be dark green, brown etcetera. and his paintings are not as 'clean' as the colouring book outlines need to be.

If there is any technique the saves me an hour of work, times 30 that's a lot of hours saved. Any suggestions please drop them in the comments below, I'll give it all a try.

(I cant drop anything high resolution here but I do have high-res tiffs myself)

enter image description here

As requested, another more high resolution example to play with. (PNG went over the 2MB max, I hope this is good enough for you?)

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    I think I would approach this in much the same way you have. I've no magic fix unfortunately, and I would doubt if there is one. This is something your should perhaps discuss with the artist. You could suggest for future work, that designs are created with black ink on white paper. Fixing stuff after it has been done is always going to be problematic and time consuming. – Billy Kerr Aug 16 '19 at 12:24
  • I've been playing around with the first image you've posted, but it's quite damaged by compression artifacts which makes it even harder than it is in the first place. Can you post a (small) part of the image in full resolution without compression? As a png perhaps? – Wolff Aug 16 '19 at 16:40
  • @Billy Kerr: if there is no one good solution at least I will feel reassured about my approach and skills. I like the artist and the work in itself is pleasantly meditative. The artist will not change his style but I can charge a little more for future works he will surely order. Funny side-note: he paints these faster than I can vector them. – Mark Aug 16 '19 at 19:35
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    I, too, can't see anything which may be easier or save some trouble. The only possible thing I could think of would be entirely dependent upon how the artist works. If he/she tends to key line things first, then go in and color -- getting a duplicate of the key line before coloring begins may help. But that's about the best I can offer. – Scott Aug 16 '19 at 19:42
  • I agree with the other comments. I've been trying different approaches with the latest example and it's just not clean enough to make a simple filtering without manually drawing or selecting. Unwanted colors are also present in the wanted stroke and it's all very grainy. – Wolff Aug 16 '19 at 20:07

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