Internal transmittance, \(\tau\), uses as reference the light
entering the object while total transmittance, \(T\), takes the incident
light as reference. The
conversion is possible only if total reflectance, \(\rho\), is known. Either as spectral
data in an object_spct
object, a filter_spct
object that is
"under-the-hood" an object_spct
, or if a fixed reflectance factor
applicable to all wavelengths is stored in the filter.properties
attribute of the filter_spct
object.
Conversions are computed as:
$$\tau = \frac{T - \rho}{1 - \rho}$$
and
$$T = \tau * (1 - \rho) + \rho$$
For the conversion to take place the object passed as argument to x
,
must contain a column with transmittance data, named Tfr
. Any
necessary conversion from absorbance A
or from Afr
into
transmittance, must be done before calling convertTfrType()
.