Skip to contents

Standard Normal Variate constructor for spectral preprocessing

Source: R/prep_snv.R
prep_snv.Rd

Creates a preprocessing constructor for applying Standard Normal Variate (SNV) normalisation to spectral data. The constructor is intended to be passed to preprocess_recipe and executed via process.

Usage

prep_snv()

Value

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

Details

SNV normalises each spectrum row-wise by subtracting its mean and dividing by its standard deviation:

\[SNV_i = \frac{x_i - \bar{x}_i}{s_i}\]

where \(x_i\) is the signal of the \(i\)th observation, \(\bar{x}_i\) is its mean and \(s_i\) its standard deviation. Implemented via standardNormalVariate.

References

Barnes RJ, Dhanoa MS, Lister SJ. 1989. Standard normal variate transformation and de-trending of near-infrared diffuse reflectance spectra. Applied spectroscopy, 43(5): 772-777.

See also

preprocess_recipe, process

Author

Leonardo Ramirez-Lopez with code from Antoine Stevens

Examples

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

snv <- prep_snv()
recipe <- preprocess_recipe(snv)
X_snv <- process(X, recipe)