spectrochempy.savgol

savgol(dataset, size=5, order=2, dim=-1, delta=None, **kwargs)[source]

Savitzky-Golay filter.

Wrapper of scpy.signal.savgol(). See the documentation of this function for more details.

Parameters:

  • dataset (NDDataset) – Input dataset to filter.

  • size (int, optional, default: 5) – The size of the smoothing window.

  • order (int, optional, default: 2) – The order of the polynomial used to fit the data. order must be less than size.

  • dim (int or str, optional, default: -1) – Axis along which to apply the filter. Accepts a dimension name (e.g. "x") or an integer index (e.g. -1 for the last axis).

  • delta (float or None, optional, default: None) – Sample spacing passed to scipy.signal.savgol_filter.

    • None (default) — when deriv > 0, the signed spacing is automatically derived from the coordinate of the processed axis if the coordinate is uniformly spaced. On a non-uniform or missing coordinate a warning is emitted and the index-based delta=1.0 is used as a fallback.

    • A numeric value — passed directly to SciPy with its sign. The value is interpreted in the current unit of the selected coordinate. No unit-based correction (_reversed) is applied. For a descending coordinate, supply a negative delta if the derivative should follow the physical axis.

    Changed in version 0.12.5: Default changed from 1.0 to None (auto-detect).

    Changed in version 0.12.5: Explicit delta is now passed to SciPy with its sign. The former _reversed unit-based correction is no longer applied when delta is explicitly provided.

  • **kwargs (keyword arguments, optional) – Additional keyword arguments passed to the filter.

Returns:

NDDataset – Smoothed data.

Other Parameters:

  • deriv (int, optional, default: 0) – The order of the derivative to compute.

  • mode (str, optional, default: ‘nearest’) – The mode parameter determines how the array borders are handled.

  • cval (float, optional, default: 0.0) – Value to fill past edges of input if mode is ‘constant’.

  • log_level (str, optional, default: ‘WARNING’) – The log level for the filter.

See also

Filter

Filter processing.

differentiate

Discoverable interface for Savitzky-Golay derivatives.

Notes

When delta is None (the default), the sample spacing is detected from the coordinate and passed directly to scipy.signal.savgol_filter. The Savitzky-Golay algorithm is fundamentally index-based; the detected delta scales the derivative coefficients during the convolution.

When delta is a numeric value, it is passed to SciPy exactly as provided, with its sign. The coordinate units (cm⁻¹, ppm, etc.) have no effect on the result in this case. The user is responsible for the sign convention.

Units. For deriv > 0 with a physically scaled delta (auto-detected from a uniform coordinate or explicitly provided when the coordinate carries units), the output units are source_units / coordinate_units**deriv. For example, a first derivative of absorbance with respect to cm⁻¹ yields absorbance·cm. Smoothing (deriv=0) and index-based fallbacks preserve the source units unchanged. If the source has no units, the result has no units regardless of the coordinate.

Changed in version 0.12.5: Units are now propagated for physically scaled derivative paths. Smoothing and index fallbacks keep source units.

Examples using spectrochempy.savgol

Savitzky-Golay derivatives on a synthetic spectrum

Savitzky-Golay derivatives on a synthetic spectrum