I was trying the last "Color Reducer and Cartoonizer" filter from Tibor95 , anyway the concept and the problem to solve remain the same for all the similar filters but for a better understanding you may be better first read this http://code.google.com/p/cartooner-colo ... troduction
Essentially a cartoon filter should
1 Reduce the number of color for a more graphic effect, and create a layer with this
2 Get the image outlines and to create a Outline layer (that ideally is transparent and go on top...but tecnically may also have a white BG , if is used darken only as merging mode )black OUTLINE
Now 2 is the most difficult...
The most apparent difficulty is get the right outlines, quite a big challenge but here the result of Tibor95 are quite good
but there is another problem not only have the "right" outlines but also have nice clean lines.
Here i get to the conviction that most of the Edge-detect algorithms were developed with in mind only forensic or anyway very technical use , and so nobody care if that lines are usually somehow ugly
For "ugly" i mean aliased , too sharp and spiky, full of little sharp angles ...some roughness may be nice in line art but that roughness looks too ...squared
Now personally i did fight long to experiment and try all sort of edge detection filter and tool (and at the end the only i found adaptable was not even a proper Edge filter but a artistic gmic filter ,pencil).
But the Tibor95 algorithm for the line art seems to give interesting results remain only , to my taste
to clean and smooth that outline:
Now ...a similar outline should be easy to convert in paths , and once converted in path the sharp angles may be rounded may be smoothed ...even stroked
Honestly i a have no much confidence with Vector , and gimp is not a vector tool , nevertheless gimp should handle paths sufficiently to allow simple operations (at least to round the most little sharp angles and make the lines smoother but neatColors
as for the colors after the "simplification" step to reduce the number of colors ... after tthat interesting option would be do the opposite and allow the simplified colors to merge softly at their borders
Also the sharp transition as now may give good effect but a new option to make the transition between the color blobs smoother would allow some nice pictorial effects
To condensate in a few wordsfor the outline
i think would be nice have a option to , automatically or interactively convert the outlines in a path to clean up or stroke , and re-import as bitmap when donefor the colors
a option to have at the borders between different colors a gradient effect
instead of the sharp transition
oh well just some idea that were buzzing in my mind...