Nearest Match

HLC Colour Atlas XL — Spectra, λ* Metrics & Nearest Match

Interactive HLC Viewer

This page provides an interactive viewer for the HLC Colour Atlas XL. Colors are organized by:

• H (Hue)
• L (Lightness)
• C (Chroma)

For each color tile you can inspect ID, H/L/C, Lab, (if available) HEX, and the measured reflectance spectrum over 380–730 nm.

Spectral metrics: λ^*_V2, λ^*_EE and Δλ^*

In addition to the spectrum R(λ), the atlas includes three compact descriptors derived from it:

1) λ^*_EE (Equal-Energy reflectance centroid)

λ^*_EE is the centroid (“center of mass”) of reflected energy in the 380–730 nm range under equal-energy weighting (no illuminant weighting):

λ*EE = ( ∫ λ · R(λ) dλ ) / ( ∫ R(λ) dλ )

Intuition: where the spectrum reflects “on average” — more toward shorter wavelengths (bluish) or longer wavelengths (reddish).

2) λ^*_V2 (Energetic equilibrium point)

λ^*_V2 is an energy-balance point between absorption and reflection. With the absorption proxy A(λ) = 1 − R(λ), λ^*_V2 is the unique wavelength that satisfies:

∫380→λ* A(λ) dλ  =  ∫λ*→730 R(λ) dλ

Intuition: the accumulated absorption on the shortwave side equals the accumulated reflection on the longwave side.

3) Δλ^* (asymmetry indicator)

Δλ* = λ*V2 − λ*EE

Intuition: Δλ^* quantifies how far the equilibrium point and the centroid differ. This acts as a simple spectral shape/asymmetry indicator, useful for comparison and sorting.

Note: The viewer/plugin does not compute these values live. Spectra and λ* metrics are already prepared in the dataset and are only loaded and displayed.

Nearest Match — comparison without spectral computation

The Nearest Match plugin finds the closest atlas entry by direct comparison and provides a ranked top list of similar candidates.

Supported inputs:

• HEX / RGB comparison (distance in RGB space; practical for screen/web)
• Lab comparison (distance in Lab space; practical for color-difference tasks)
• λ* comparison (absolute difference in nm for λ^*_V2, λ^*_EE or Δλ^*)

“No computation” means:

• no spectrum parsing, no λ* recomputation,
• only comparisons against existing atlas fields (ranking).

Technical note on color appearance

On-screen color appearance depends on display calibration, browser, and color management. For production (e.g., print), measured values and standardized viewing/measurement conditions remain decisive.