How did you protect against overfitting? How about local maxima? Some of your constants look surprising to say the least.
Most notably:
* The gamma value of 0.38 (when most studies suggest 1.5 - 2.5 for human eye gamma)
* The significant difference in the vertical and horizontal constants (when as far as I know human eyes are equally sensitive to most distortions independant of angle).
There was a large variety of regularization and optimization techniques used. An embarrassingly large amount of manual work went into both.
In this use the gamma is the inverse of something close to 2.6. Butteraugli needs both gamma correction and inverse gamma correction.
The FFT co-efficients only look weird, but they should actually lead to a symmetric result if our math is correct. In a future version we move away from the FFT, so I don't encourage anyone to actually debug that too much.
Nothing to be embarrassed about, you got results. Results are what matters in the end.
This is even more the case with software. If this cost 20 or 20 million man hours is irrelevant in the long run because eventually it will be used enough to offset costs if it is as good as every one says. Of course short term cost hurt now, but sounds like you still had computers do much of the heavy lifting.
Most notably:
* The gamma value of 0.38 (when most studies suggest 1.5 - 2.5 for human eye gamma)
* The significant difference in the vertical and horizontal constants (when as far as I know human eyes are equally sensitive to most distortions independant of angle).