Reflectance/absorbance conversion constructor for spectral preprocessing

Creates a preprocessing constructor for converting spectral data between reflectance and absorbance. The constructor is intended to be passed to preprocess_recipe and executed via process.

Usage

prep_transform(to = c("absorbance", "reflectance"))

Arguments

to

A character string specifying the target unit. Either "absorbance" (default) or "reflectance".

Value

An object of class preprocessing to be used in preprocess_recipe and executed by process.

Details

Conversion follows Beer's Law:

\[A = -\log_{10}(R)\]

where \(A\) is absorbance and \(R\) is reflectance.

When converting to absorbance, all values in X must be strictly positive. A warning is issued if the resulting absorbance contains small negative values, which may indicate precision or scaling issues in the input.

Note that no check is performed on whether the input is actually in the expected unit (the transformation is applied as specified).

See also

preprocess_recipe, process

Author

Leonardo Ramirez-Lopez

Examples

data("NIRcannabis")
X <- NIRcannabis$spc # absorbance

tr <- prep_transform(to = "reflectance")
recipe <- preprocess_recipe(tr, device = "proxiscout")
X_ref <- process(X, recipe)