> Mike, do you think the Nearest is in fact the correct interpolant to use, or am I barking up the wrong tree here?

I wouldn't have thought Nearest would be the correct interpolant, but like I said, I don't have good intuition here.  What's the logic for using Nearest instead of Linear?

OK, thinking about it a bit, I guess if the CF is uncorrelated, then Nearest would match my Pixel representation, so that could make sense.  Or maybe your investigation here is evidence that my thought of using Pixel for UCF is wrong.

Interestingly, if I change the interpolant to _anything_ besides Linear (I tried Nearest, Cubic, Quintic, Lanczos 5, and 7), it also fails.  So perhaps this might be a case of the test passing by a bit of luck.  It seems unlikely to me the Linear is so precisely the correct interpolant that nothing else works correctly.  Maybe we just got lucky with the rng choice or something.

(I checked this last possibility by changing the rseed value from 12345 to 1234567, and there were two failures, but not this one.  Using rseed=0 (to use the time) and running a bunch of times, it didn't fail for me, so maybe that idea is a red herring.)