aug_band_perturb — Local band gain-and-offset perturbation

Group: Augmentation · C ABI: n4m_augmentation_band_perturb_*

Description

Random band-local gain and offset perturbations.

Parameters

Name

Type

Default

n_bands

int

3

bw_lo

int

5

bw_hi

int

15

gain_lo

float

0.9

gain_hi

float

1.1

offset_lo

float

-0.01

offset_hi

float

0.01

rng

Optional[PCG64]

None

seed

int

0

API and bindings

C ABI (ABI 2): n4m_augmentation_band_perturb_apply · n4m_augmentation_band_perturb_create · n4m_augmentation_band_perturb_destroy. Use the linked public header for the exact signature, configuration, and result handles.

Python (verified public re-export):

from n4m.augmentation.spectral import BandPerturbationAugmenter

Source signature: BandPerturbationAugmenter(n_bands: int = 3, bw_lo: int = 5, bw_hi: int = 15, gain_lo: float = 0.9, gain_hi: float = 1.1, offset_lo: float = -0.01, offset_hi: float = 0.01, rng: Optional[PCG64] = None, seed: int = 0).

R: no current source-verified entry point was found for this catalog method.

MATLAB / Octave: no current source-verified entry point was found for this catalog method.

Explanations

Bibliographic source

No canonical paper specifies this bandwise affine perturbation. It is a native spectral corruption heuristic related to offset/gain augmentation.

Mathematical principle

For each row and each of n_bands, draw a center, width \(w\), gain \(g\) and offset \(a\). Within the clipped band, update values sequentially as \(X'_{ij}=gX_{ij}+a\). Parameter ranges bw_*, gain_*, and offset_* control extent and amplitude.

Appropriate uses

Robustness to wavelength-local sensitivity and baseline changes.

Limits and validation

Band boundaries are abrupt and overlapping bands compound in draw order. The operator exposes per-sample variation only, not one shared perturbation per batch.

Implementation

Python role API n4m.augmentation.spectral.BandPerturbationAugmenter; ABI 2 family n4m_augmentation_band_perturb_{create,apply,destroy}.

The ABI-2 implementation is the n4m_augmentation_band_perturb_* lifecycle in libn4m.

Sources and provenance

https://github.com/GBeurier/nirs4all-methods/blob/main/cpp/src/core/augmentation/spectral/band_perturb.h

See also: methods index · interactive dashboard