Skip to content

Kreft’s Dichromaticity Index

A paired CIELAB hue-shift measure comparing a transparent sample's maximal-chroma state with fourfold lighter/thinner and darker/thicker states to quantify dichromatism.

Version
v3 · 2026-09-19 · History
Domain-specific #
2144
Domain group
Natural Sciences
Origin domain
Physics
Subdomain
Colorimetry → Physics
Aliases
Kreft dichromaticity index, DI L and DI D

Core Idea

Kreft’s dichromaticity index quantifies dichromatism: a transparent material's change in perceived hue as optical path length or concentration changes. A transmission spectrum is converted to CIELAB coordinates across a dilution or thickness series. The reference state is the concentration–path-length product \(x_*\) at which chroma \(C^*_{ab}\) is maximal. Two signed hue differences are then computed:

\[ DI_L=\Delta h_{ab}(x_*,x_*/4),\qquad DI_D=\Delta h_{ab}(x_*,4x_*), \]

for lighter/thinner and darker/thicker directions respectively.

How would you explain it like I'm…

The Color-Changing Juice Score

Some see-through colored liquids look like one color when there is a little and a different color when there is a lot. Kreft's Dichromaticity Index is a way to measure how much the color changes. You find the amount where the color looks strongest, then check how the color shifts with much less and much more.

Thick-or-Thin Shade Shift

Some clear, colored materials change their color, not just how dark they are, when they get thicker or more concentrated. This is called dichromatism. Kreft's Dichromaticity Index measures it. Scientists find the thickness where the color is most vivid, then compare it with a sample a quarter as thick and one four times as thick. They get two numbers: how much the color turns going lighter, and how much it turns going darker.

Two-Way Hue Shift Index

Kreft's Dichromaticity Index measures dichromatism: a transparent material's change in perceived hue as its thickness or concentration changes. You measure light transmission through a series of thicknesses or dilutions and convert each spectrum into CIELAB color coordinates, which describe color roughly as people perceive it. The reference point is the concentration-times-path-length value where chroma, meaning colorfulness, is highest. You then compute the signed hue-angle change going to one quarter of that value (lighter direction) and to four times it (darker direction). Keeping two numbers matters because a material can shift differently in the two directions, and the sign depends on the convention for measuring hue-angle differences.

 

Kreft's Dichromaticity Index quantifies dichromatism, the change in perceived hue of a transparent material as optical path length or concentration varies. One measures transmission spectra across a dilution or thickness series and converts each to CIELAB coordinates. The anchor is the concentration–path-length product x* at which the chroma C*ab is maximal. Two signed hue-angle differences are then computed: DI_L, the hue difference between x* and x*/4 (lighter/thinner), and DI_D, between x* and 4x* (darker/thicker). Reporting the ordered pair preserves directional asymmetry, since dilution and concentration can shift hue differently. The sign follows a declared shortest signed hue-angle convention. The identifying recipe is: spectral series, CIELAB conversion, maximal-chroma anchor, fixed fourfold perturbations, and two signed hue changes.

Scope of Application

The measure applies to dyes, pigments in transparent media, oils, biological chromophores, and other samples whose visible spectra yield systematic hue change with optical density. Pumpkin seed oil is a canonical high-dichromatism example. Its spectral-to-perceptual translation follows standard color-science practice rather than direct wavelength labeling.

Application assumes reproducible spectral data and meaningful CIELAB conversion. Scattering, fluorescence, chemical change across dilution, aggregation, or departure from the optical model can mix other phenomena into the result.

Clarity

Report sample preparation, solvent, temperature, path length or concentration, spectral instrument, illuminant, observer, white reference, CIELAB convention, interpolation method, maximal-chroma estimate, hue unwrapping, and sign orientation. Publish both \(DI_L\) and \(DI_D\); a single unsigned magnitude loses information.

Manages Complexity

The paired index reduces a full spectral and color trajectory to two interpretable angular displacements while anchoring comparisons at the sample's most saturated state. Fixed fourfold changes support reproducibility across samples whose absolute concentration scales differ.

Abstract Reasoning

  1. Measure or model visible spectra across a sufficient optical-density range.
  2. Convert each spectrum under fixed colorimetric conditions.
  3. Compute chroma and circular hue angle.
  4. Locate or interpolate the maximal-chroma state \(x_*\).
  5. Evaluate colors at \(x_*/4\) and \(4x_*\).
  6. Compute signed shortest hue differences with consistent wrapping.
  7. Preserve the lighter and darker components separately.
  8. Quantify sensitivity to spectral noise, interpolation, and colorimetric settings.
  9. Check that chemistry and scattering remain stable across the series.

Knowledge Transfer

The portable pattern is anchor a nonlinear trajectory at its maximum salience, perturb the controlling scale symmetrically in log space, and retain directional response. It transfers to paired sensitivity indices, hysteresis-free path summaries, dose–response characterization, and multiscale feature change. The proposed immediate parent is Measurement.

Relationships to Other Abstractions

Local relationship map for Kreft’s Dichromaticity IndexParents appear above the current abstraction, mutual partners to the right, and children below. Node labels state whether each abstraction is prime or domain-specific; colors identify relation types.Kreft’sDichromaticity IndexDOMAINPrime abstraction: Measurement — is a kind ofMeasurementPRIME

Current abstraction Kreft’s Dichromaticity Index Domain-specific

Parents (1) — outgoing typed relations

  • Kreft’s Dichromaticity Index is a kind of Measurement Prime

    Measurement is the broader abstraction this entry instantiates.

Hierarchy path (1) — routes to 1 parentless root

  • Kreft’s Dichromaticity Index → is a kind of Measurement

Neighborhood in Abstraction Space

Kreft’s Dichromaticity Index sits in a sparse region of the domain-specific corpus (96th percentile for distinctiveness): few abstractions share its structure, so a faithful description tends to retrieve it precisely.

Family — Unclustered & Miscellaneous (2769 abstractions)

Nearest neighbors

Computed from structural-signature embeddings · 2026-10-25