Color.Lab (Color v0.4.0)

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CIE 1976 L*a*b* color space.

Conversions between L*a*b* and XYZ use the formulas published by Bruce Lindbloom (http://www.brucelindbloom.com/index.html?Math.html) with the exact CIE constants ε = 216/24389 and κ = 24389/27. The approximate 0.008856 / 7.787 forms found in many online references are not used.

Summary

Types

t()

Functions

from_xyz(xyz)

Converts a CIE XYZ color to an L*a*b* color.

to_xyz(lab, options \\ [])

Converts an L*a*b* color to a CIE XYZ color.

Types

t()

@type t() :: %Color.Lab{
  a: number() | nil,
  alpha: number() | nil,
  b: number() | nil,
  illuminant: atom(),
  l: number() | nil,
  observer_angle: 2 | 10
}

Functions

from_xyz(xyz)

Converts a CIE XYZ color to an L*a*b* color.

Arguments

  • xyz is a Color.XYZ struct. Its :illuminant and :observer_angle fields select the reference white.

Returns

  • A Color.Lab struct tagged with the same illuminant and observer angle as the input xyz.

Examples

iex> xyz = %Color.XYZ{x: 0.95047, y: 1.0, z: 1.08883, illuminant: :D65, observer_angle: 2}
iex> {:ok, lab} = Color.Lab.from_xyz(xyz)
iex> {Float.round(lab.l, 3), Float.round(lab.a, 3), Float.round(lab.b, 3)}
{100.0, 0.0, 0.0}

to_xyz(lab, options \\ [])

Converts an L*a*b* color to a CIE XYZ color.

Arguments

  • lab is a Color.Lab struct.

  • options is a keyword list.

Options

  • :illuminant overrides the reference-white illuminant from the lab struct. Defaults to lab.illuminant.

  • :observer_angle overrides the observer angle (2 or 10). Defaults to lab.observer_angle.

Returns

  • A Color.XYZ struct whose Y is on the same scale as the reference white (typically Y ∈ [0, 1]).

Examples

iex> {:ok, xyz} = Color.Lab.to_xyz(%Color.Lab{l: 100.0, a: 0.0, b: 0.0})
iex> {Float.round(xyz.x, 4), Float.round(xyz.y, 4), Float.round(xyz.z, 4)}
{0.9505, 1.0, 1.0888}