Here is a suggestion UI project for training purpose:
Right now, in GEGL, you have access to the whole 2-parameter family of
cubic splines for resampling, as well as bilinear.
Pick three representatives, say Catmull-Rom ("lots" of halo),
smoothing B-Splines ("lots" of blur) and bilinear ("lots" of jaggies).
(Instead of bilinear you could use nohalo a.k.a. gegl-sampler-sharp.c.)
If you want to stick to what's already in the Gimp you could use
lanczos, cubic and bilinear.
Now: Any location within a triangle defines barycentric coordinates,
which in term define a "blending" of the three methods.
Construct an interface which mimicks
except that instead of using it as a descriptive tool, we use it as a
way of "picking your blend of poison."
Now, I don't know how attractive it is to ask people to pick a method
by focusing on their weaknesses, but it certainly is a realistic way.
Also note that this interface would allow one to drive any triad of
resampling methods which can be compared and characterized in terms of
the three common artifacts.
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