This seems to be optimizing for a "perceptual loss function" over in https://github.com/google/butteraugli/blob/master/butteraugl...

Looking at the code to that, it looks like 1500 lines of this:

    double MaskDcB(double delta) {
      PROFILER_FUNC;
      static const double extmul = 0.349376011816;
      static const double extoff = -0.894711072781;
      static const double offset = 0.901647926679;
      static const double scaler = 0.380086095024;
      static const double mul = 18.0373825149;
      static const std::array<double, 512> lut =
          MakeMask(extmul, extoff, mul, offset, scaler);
      return InterpolateClampNegative(lut.data(), lut.size(), delta);
    }

The code has hundreds of high precision constants. Some even seem to be set to nonsensical values (like kGamma to 0.38) Where did all of them come from? The real science here seems to be the method by which those constants were chosen, and I see no details how it was done.