Table 3.

NNI estimation from encoder feature extraction results to MLR.

Transformation spectrum	R2of Training set	RMSE of Training set	R2of Test set	RMSE of Test set
Original spectrum	0.490	0.110	0.394	0.124
Logarithmic Spectrum	0.471	0.116	0.477	0.095
Difference Spectrum	0.532	0.131	0.428	0.121
Log difference spectra	0.612	0.116	0.620	0.104