prep_smooth: Smoothing constructor for spectral preprocessing

In proximetricsR: Spectral Preprocessing and Chemometric Calibration of NIR Sensors

Smoothing constructor for spectral preprocessing

Description

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Creates a preprocessing constructor for smoothing spectral data. The constructor is intended to be passed to preprocess_recipe and executed via process.

Two algorithms are supported: Savitzky-Golay ("savitzky-golay") and moving average ("moving-average").

Usage

prep_smooth(w, p = NULL, algorithm = c("savitzky-golay", "moving-average"))

Arguments

w	A positive odd integer specifying the filter window size.
p	An integer specifying the polynomial order. Required when algorithm = "savitzky-golay". Must satisfy p < w and p >= 0. Ignored for "moving-average".
algorithm	A character string specifying the smoothing algorithm. One of "savitzky-golay" (default) or "moving-average". See Details.

Details

Savitzky-Golay ("savitzky-golay"): fits a polynomial of order p within a moving window of size w and returns the zero-order coefficient (i.e. the smoothed value). Implemented via savitzkyGolay with m = 0.

Moving average ("moving-average"): computes a simple moving average of window size w using movav. Edge values are handled using progressively narrower windows so the output has the same number of columns as the input. This reproduces the "Smooth" pre-treatment from BUCHI NIRWise PLUS.

For "moving-average", the NIRWise PLUS half-window convention is: \mjdeqnhalf_w = (w - 1) / 2half_w = (w - 1) / 2 stored internally for device file serialization and not user-facing.

Value

An object of class preprocessing to be used in preprocess_recipe and executed by process. The object is a list containing the method name and all parameters. For algorithm = "moving-average", the NIRWise PLUS half-window value (half_w) is also stored for device file serialization.

Author(s)

Leonardo Ramirez-Lopez and Claudio Orellano

See Also

preprocess_recipe, process

Examples

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

# Savitzky-Golay smoothing, window 11, polynomial order 3
sg <- prep_smooth(w = 11, p = 3, algorithm = "savitzky-golay")

# Moving average smoothing, window 7
ma <- prep_smooth(w = 7, algorithm = "moving-average")

# Apply via preprocess_recipe
recipe <- preprocess_recipe(sg, device = "proxiscout")
X_smooth <- process(X, recipe)

proximetricsR documentation built on Sept. 4, 2026, 5:08 p.m.