Color.Distance (Color v0.4.0)

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Color difference (ΔE) metrics between two colors.

Each function accepts two colors in any supported color space; inputs that are not already in L*a*b* are converted via Color.convert/2, chromatically adapting to D65 as necessary.

The supported metrics are:

  • delta_e_76/2 — CIE76, the original simple Euclidean distance in L*a*b*. Fast but known to be perceptually non-uniform, especially in saturated blue-purple regions.

  • delta_e_94/3 — CIE94, a weighted distance that corrects the saturation/hue issues of CIE76. Parametric factors default to the graphic-arts application (kL = 1, K1 = 0.045, K2 = 0.015).

  • delta_e_2000/3 — CIEDE2000, the modern standard. Much more complex but handles perceptual non-uniformity well.

  • delta_e_cmc/3 — CMC l:c, developed by the Colour Measurement Committee of the Society of Dyers and Colourists. Common in the textile industry.

For most use cases prefer delta_e_2000/3.

Summary

Functions

delta_e_76(a, b)

CIE76 color difference — Euclidean distance in L*a*b*.

delta_e_94(a, b, options \\ [])

CIE94 color difference.

delta_e_2000(a, b, options \\ [])

CIEDE2000 color difference.

delta_e_cmc(a, b, options \\ [])

CMC l:c color difference.

Functions

delta_e_76(a, b)

@spec delta_e_76(Color.input(), Color.input()) :: float()

CIE76 color difference — Euclidean distance in L*a*b*.

Arguments

  • a is any supported color.

  • b is any supported color.

Returns

  • A non-negative float.

Examples

iex> Color.Distance.delta_e_76(%Color.Lab{l: 50.0, a: 0.0, b: 0.0}, %Color.Lab{l: 50.0, a: 0.0, b: 0.0})
0.0

iex> Float.round(Color.Distance.delta_e_76(%Color.Lab{l: 50.0, a: 2.6772, b: -79.7751}, %Color.Lab{l: 50.0, a: 0.0, b: -82.7485}), 4)
4.0011

delta_e_94(a, b, options \\ [])

@spec delta_e_94(Color.input(), Color.input(), keyword()) :: float()

CIE94 color difference.

Arguments

  • a is any supported color.

  • b is any supported color.

  • options is a keyword list.

Options

  • :application is :graphic_arts (default) or :textiles and picks the CIE94 kL, K1, K2 constants.

  • :kL, :kC, :kH are parametric weighting factors (defaults 1.0, 1.0, 1.0).

Returns

  • A non-negative float.

Examples

iex> Float.round(Color.Distance.delta_e_94(%Color.Lab{l: 50.0, a: 2.6772, b: -79.7751}, %Color.Lab{l: 50.0, a: 0.0, b: -82.7485}), 4)
1.3950

delta_e_2000(a, b, options \\ [])

@spec delta_e_2000(Color.input(), Color.input(), keyword()) :: float()

CIEDE2000 color difference.

Reference: Sharma, Wu & Dalal, "The CIEDE2000 Color-Difference Formula: Implementation Notes, Supplementary Test Data, and Mathematical Observations" (2005).

Arguments

  • a is any supported color.

  • b is any supported color.

  • options is a keyword list.

Options

  • :kL, :kC, :kH are parametric weighting factors (defaults 1.0, 1.0, 1.0).

Returns

  • A non-negative float.

Examples

iex> Float.round(Color.Distance.delta_e_2000(%Color.Lab{l: 50.0, a: 2.6772, b: -79.7751}, %Color.Lab{l: 50.0, a: 0.0, b: -82.7485}), 4)
2.0425

iex> Float.round(Color.Distance.delta_e_2000(%Color.Lab{l: 50.0, a: 2.5, b: 0.0}, %Color.Lab{l: 73.0, a: 25.0, b: -18.0}), 4)
27.1492

delta_e_cmc(a, b, options \\ [])

@spec delta_e_cmc(Color.input(), Color.input(), keyword()) :: float()

CMC l:c color difference.

Arguments

  • a is any supported color.

  • b is any supported color.

  • options is a keyword list.

Options

  • :l is the lightness weighting factor. Defaults to 2.0 (acceptability). Use 1.0 for perceptibility.

  • :c is the chroma weighting factor. Defaults to 1.0.

Returns

  • A non-negative float.

Examples

iex> Float.round(Color.Distance.delta_e_cmc(%Color.Lab{l: 50.0, a: 2.6772, b: -79.7751}, %Color.Lab{l: 50.0, a: 0.0, b: -82.7485}), 4)
1.7387