>Psychtoolbox>PsychColorimetric

[absorptanceSpectra, absorptanceSpectraWls] =…
AbsorbanceToAbsorptance(absorbanceSpectra, absorbanceSpectraWls, axialOpticalDensities)

Convert pigment absorbance spectra into absorptance spectra, using the peak axial
optical density. The absorbance/absorptance terminology is described at the
CVRL web page, http://cvrl.ucl.ac.uk. Wyszecki and Stiles refere to absorbance
the absorption coefficient (p. 588).

Both absorptance spectra and absorbance spectra describe quantal absorption.

Absorbance spectra are normalized to a peak value of 1.
Absorptance spectra are the proportion of quanta actually absorbed.

Equation: absorptanceSpectra = 1 - 10.^(-OD * absorbanceSpectra)

Multiple spectra may be passed in the rows of absorbanceSpectra. If
so, then the same number of densities should be passed in the vector
axialOpticalDensities, and multiple answers are returned in the rows
of absorptanceSpectra.

Wavelength information may be in any of the available Psychtoolbox representations,
and the returned wavelength information is in the same format as passed.

A useful fact about this conversion is the following. For small axial optical densities
the absorptance spectrum is a scaled version of the absorbance spectrum. This follows
if we take the Taylor expansion of 1 - 10.^(-x) for small values of x. We find that
that is 1 - (10^0 + (-ln(10)*x) = ln(10)*x. Plugging in OD*absorbanceSpectra for x
we get the absorptanceSpectra = ln(10)*OD*absorbanceSpectra.

04/29/03 lyin Wrote wrote with advice from dhb
04/30/03 lyin Reorganize the variable
06/12/03 lyin Change the way variable being passed
06/23/03 dhb Check dimensions of spectra and density.
06/30/03 dhb Change to toolbox convention, put sensitivity like stuff in rows.
08/11/13 dhb Fix comment to reflect row convention change made in 2003. Slowly but surely we fix things up.
10/29/13 dhb, ms Add commment about absorptance for low OD.
12/02/13 dhb Fix spelling of “absorptance” in routine names and throughout.