Cubic interpolation bug

[zavinator]

Hi, I have some strange artifacts with built-in cubic interpolation. It is OK when using my cubic interpolation (see https://code.google.com/p/field3d/issues/detail?id=21&can=1&q=cubic). Don't know if it could be a regression of that bug.
I can't post here a F3D cache, because it is too large and probably copyrighted, but please take a look on your interpolation class CubicFieldInterp...

[magnusw]

Hi, could you describe the artifacts? Maybe attach a cropped image of just that one element?

One thing to note is that the Cubic interpolators actually implement Monotonic Cubic interpolation (poor naming...)

[zavinator]

I don't have these renders, but the problem was at the border of the smoke. If I have increased the gamma of the render with cubic interpolation, it shows that there are some strange low intensity areas outside the main smoke (next to the smoke border, but fully inside the container). Without cubic interpolation, these areas are correctly black...
Sorry for very poor description. I'll try to make a reproducible example, when I have time...