aug_emsc_distort — Random EMSC-like affine and polynomial distortion

Group: Augmentation · C ABI: n4m_augmentation_emsc_distort_*

Description

Random EMSC-like multiplicative, additive and polynomial distortion.

Parameters

Name

Type

Default

mult_low

float

0.9

mult_high

float

1.1

add_low

float

-0.05

add_high

float

0.05

polynomial_order

int

2

polynomial_strength

float

0.02

correlation

float

0.3

wavelengths

—

None

rng

Optional[PCG64]

None

seed

int

0

API and bindings

C ABI (ABI 2): n4m_augmentation_emsc_distort_apply · n4m_augmentation_emsc_distort_create · n4m_augmentation_emsc_distort_destroy. Use the linked public header for the exact signature, configuration, and result handles.

Python (verified public re-export):

from n4m.augmentation.scattering import EMSCDistortionAugmenter

Source signature: EMSCDistortionAugmenter(mult_low: float = 0.9, mult_high: float = 1.1, add_low: float = -0.05, add_high: float = 0.05, polynomial_order: int = 2, polynomial_strength: float = 0.02, correlation: float = 0.3, wavelengths = None, 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

Martens & Stark (1991), Extended multiplicative signal correction and spectral interference subtraction, Journal of Pharmaceutical and Biomedical Analysis 9, 625–635, DOI 10.1016/0731-7085(91)80188-F (https://doi.org/10.1016/0731-7085(91)80188-F). This operator generates EMSC-shaped distortions; it does not perform EMSC correction.

Mathematical principle

Normalize wavelength to \(t\in[-1,1]\). Draw clipped multiplicative \(b_i\) and an additive \(a_i\) whose mean is correlated with the standardized \(b_i\) deviation. For orders \(k=1..q\), draw \(c_{ik}\sim N(0,s^2/k)\) and return \(X'_i=a_i+b_iX_i+\sum_k c_{ik}t^k\).

Appropriate uses

Training against correlated additive, multiplicative, and smooth baseline scatter effects.

Limits and validation

Ranges are converted to mean and one-quarter-range standard deviations, then clipped; they are not uniform draws. Required wavelengths must span a nonzero range.

Implementation

Python role API n4m.augmentation.scattering.EMSCDistortionAugmenter; ABI 2 family n4m_augmentation_emsc_distort_{create,apply,destroy}.

The ABI-2 implementation is the n4m_augmentation_emsc_distort_* lifecycle in libn4m.

Sources and provenance

https://github.com/GBeurier/nirs4all-methods/blob/main/cpp/src/core/augmentation/scattering/emsc_distort.h; https://doi.org/10.1016/0731-7085(91)80188-F

See also: methods index · interactive dashboard