How to achieve this cartoon effect in GIMP?
Here is a short guide on how to manually create a comic style image from a photo with standard Gimp (i.e. without the aid of plugins in addition to those that come in a default Gimp 2.0 installation).
Make color gradients within the photo smooth, remove details.
- Choose Filter > Enhance > Despeckle with rather high settings for radius and adaptive unticked.
- Make image still smoother with the Filter > Blur > Selective Gaussian Blur
Reduce the colours to < 24 by transforming to indexed with Image > Mode > Indexed > Generate optimized palette 24 colours
Manually remove unwanted colors from the flat areas (e.g. in the face) by choosing Select by color and using the Bucket Fill-Tool with the colour that should stay.
- Transform the image back to RGB (Image > Mode)
Further smooth the resulting outlines using Filter > Enhance > Despeckle
When similar steps were applied to your sample image it may look similar to this:
Above image was done in a very rough and quick fashion. With subtle fine-tuning on the blur settings, color palettes, and manual removal of unwanted colors we will of course get better results.
For completeness, here's some of the G'MIC filters for cartoon-like effects:
Filters do not make it. You must manually draw paths and fill the areas with solid colors. I have done it numerous times.
Not asked, but Inkscape has much better drawing tools for this. Lock the photo and use the pen to draw the needed closed paths and separate lines. Occasionally you can also draw rectangles and circles.
In extremely lucky cases bitmap tracing (Path > Trace Bitmap) can find just the shapes you need. This is rare, mostly the tracing results need much more editing than drawing what you want.
Everything stays editable, layers and groups help keeping the control. Objects panel is the central place to make selections, hide and lock things and change the layering order.
In Inkscape snaps are easily turned ON and OFF as the drawing work demands.
The underlying shape need not to be exact where another shape covers it.
Finally: the result is freely scalable vector drawing.
See an example (Inkscape)
The nodes were inserted by clicking with the pen one node per second. The node tool moves, inserts, deletes nodes and makes changes between sharp corner - smooth curvature. As the skills develope, one draws(=drags the curvature handles) also smooth curves directly with the pen.
If you want, you can do the same with the pen in GIMP, too, but everything is a little more rigid and then result is finally a bitmap image.
ADD: This is a slightly different case, but can also be interesting