Derivatives
This package contains two common algorithms for calculating derivatives in spectroscopy:
Savitzky-Golay derivative
Savitzky-Golay derivative is a preprocessing technique in spectroscopy that calculates the derivative of a spectrum by fitting a polynomial to a window of adjacent points and calculating the derivative of the polynomial.
Arguments:
| Argument | Description | Type | Default |
|---|---|---|---|
window_size | The length of the window. Must be an odd integer number. | int | 5 |
polynomial_order | The order of the polynomial used to fit the samples. Must be less than window_size. | int | 2 |
derivative_order | The order of the derivative to compute. | int | 1 |
mode | The mode of the boundary. Options are 'nearest', 'constant', 'reflect', 'wrap', 'mirror', 'interp'. See the scipy.savgol_filter for more information. | str | 'nearest' |
Usage example:
from chemotools.derivative import SavitzkyGolay
sg = SavitzkyGolay(window_size=15, polynomial_order=2, derivate_order=1)
spectra_derivative = sg.fit_transform(spectra)
Plotting example:
William Norris derivative
William Norris derivative is a preprocessing technique in spectroscopy that calculates the derivative of a spectrum using finite differences.
Arguments:
| Argument | Description | Type | Default |
|---|---|---|---|
window_size | The length of the window. Must be an odd integer number. | int | 5 |
gap_size | The number of points between the first and second points of the window. | int | 3 |
derivative_order | The order of the derivative to compute. | int | 1 |
mode | The mode of the boundary. Options are 'nearest', 'constant', 'reflect', 'wrap', 'mirror', 'interp'. See the scipy.ndimage.convolve for more information. | str | 'nearest' |
Usage example:
from chemotools.derivative import NorrisWilliams
nw = NorrisWilliams(window_size=15, gap_size=3, derivative_order=1)
spectra_derivative = nw.fit_transform(spectra)