convolvewith: Convolve each spectrum in a colorSpec object with a kernel

Description

This function convolves each spectrum in a colorSpec object with a kernel of odd length. Its primary purpose is to correct raw spectrometer data (with positive instrumental bandwidth) to have bandwidth=0. Two popular correction kernels for this, with lengths 3 and 5, are built-in options, see Details.

Usage

"convolvewith"( x, coeff )

Arguments

a colorSpec object with N wavelengths

coeff

a convolution kernel of odd length. The center entry of this vector is taken as index 0 in the convolution. coeff can also be the string 'SS3' which means to apply the Stearns&Stearns bandwidth correction kernel coeff=c(-1,14,-1)/12, see Details. coeff can also be the string 'SS5' which means to apply the Stearns&Stearns bandwidth correction kernel coeff=c(1,-12,120,-12,1)/98, see Details.

Value

a colorSpec object with the same dimensions, wavelength, quantity, and organization. If coeff is invalid it is an ERROR and convolvewith returns NULL.

Details

The built-in kernels, 'SS3' and 'SS5', were derived by Stearns & Stearns under specific hypotheses on the spectrometer profile, bandpass, and pitch; see References. Missing values at both ends are filled by copying from the nearest valid value.

References

Stearns, E.I., Stearns R.E. An example of a method for correction radiance data for bandpass error. Color Research and Application. 13-4. 257-259. 1988.

Schanda, Janos. CIE Colorimetry, in Colorimetry: Understanding the CIE System. Wiley Interscience. 2007. p. 124.

Oleari, Claudio, Gabriele Simone. Standard Colorimetry: Definitions, Algorithms and Software. John Wiley. 2016. p. 309.