Module spectral_kernel 

P7.0 — Spectral-space kernel: SPD/CMF POD types + CIE linear-projection. P7.0 — Spectral-space kernel: SPD/CMF POD types + the CIE linear-projection contract.

This module defines the foundational spectral types and the linear projection from a Spectral Power Distribution (SPD) to CIE 1931 XYZ tristimulus values via tabulated Colour Matching Functions (CMFs).

EMF → Colour pipeline

The Qualia 10D tensor’s spectral axes [α, μ, σ] represent the EMF (electromagnetic field) payload:

• α (amplitude): total radiant power scaling
• μ (modulation): spectral bandwidth / phase modulation
• σ (signature): peak wavelength selector (400–700 nm)

The pipeline is:

EMF [α, μ, σ] → SPD(λ) → CIE XYZ → linear sRGB → display sRGB

1. emf_to_spd(α, μ, σ) constructs an SPD from the EMF payload.
2. spd_to_xyz(spd) projects through the tabulated CIE 1931 CMFs.
3. xyz_to_linear_srgb(xyz) applies the standard XYZ→sRGB matrix.

CIE 1931 2-degree observer

The CMFs are tabulated at 10 nm intervals from 380–780 nm (41 samples). This replaces the Gaussian approximation in render/spectral.rs with the authoritative tabulated data. The ΔE between the two is documented.

Determinism

All operations are deterministic: identical input → bit-identical output. The CMF tables are compile-time constants.

Structs

LinearRgb

Linear sRGB (no gamma encoding). POD, f32.

Spd

Spectral Power Distribution: radiant power at 41 wavelength samples (380–780 nm, 10 nm steps). POD, zero-heap, stack-allocated.

Xyz

CIE XYZ tristimulus values. POD, f32.

Constants

CIE_1931_CMF_X

CIE 1931 2-degree observer colour matching functions, tabulated at 10 nm intervals from 380–780 nm.

CIE_1931_CMF_Y

CIE_1931_CMF_Z

CIE_D65_X

CIE D65 illuminant white point (normalised, Y=1).

CIE_D65_Y

CIE_D65_Z

LAMBDA_MAX

Ending wavelength (nm).

LAMBDA_MIN

Starting wavelength (nm).

LAMBDA_STEP

Wavelength step (nm).

SPD_SAMPLES

Number of spectral samples (380–780 nm at 10 nm intervals).

Functions

delta_e_76

CIE76 ΔE colour difference between two XYZ values (in Lab space).

emf_to_linear_rgb

Full EMF → linear sRGB pipeline.

emf_to_spd

Convert an EMF payload [α, μ, σ] to a Spectral Power Distribution.

flat_spd_to_xyz

Project a flat (equal-energy) SPD to verify the D65 white point.

gaussian_vs_tabulated_delta_e

Compute the ΔE between the tabulated CMF projection and the existing Gaussian approximation in render::spectral.rs.

linear_rgb_to_display

Convert linear sRGB to 8-bit display sRGB (gamma-encoded, normalised).

linear_to_srgb_channel

Apply sRGB gamma encoding to a single linear channel.

spd_to_xyz

Project an SPD through the CIE 1931 2-degree CMFs to obtain XYZ tristimulus values.

xyz_to_lab

Convert XYZ to CIELAB (D65 reference white).

xyz_to_linear_srgb

Convert CIE XYZ to linear sRGB using the standard sRGB matrix.