package color

import "math"

// TODO:

// 2000

// CMC

// HCT

// ITP

// EJz

// DeltaDistance computes the Euclidean distance in the provided color space.

func DeltaDistance(reference, sample Color, space *Space) float64 {

ref := reference.Convert(space)

s := sample.Convert(space)

Δ0 := ref.Values[0] - s.Values[0]

Δ1 := ref.Values[1] - s.Values[1]

Δ2 := ref.Values[2] - s.Values[2]

return math.Hypot(math.Hypot(Δ0, Δ1), Δ2)

}

// DeltaE76 computes the CIE 1976 color difference using the Euclidean distance

// in the [Lab] color space.

func DeltaE76(reference, sample Color) float64 {

return DeltaDistance(reference, sample, Lab)

}

// DeltaEOK computes the color difference using the Euclidean distance in the

// [Oklab] color space.

func DeltaEOK(reference, sample Color) float64 {

return DeltaDistance(reference, sample, Oklab)

}

// DeltaEOK2 computes the color difference using the Euclidean distance in the

// [Oklab] color space, with the a and b axes scaled by a factor of 2, for

// better uniformity.

func DeltaEOK2(reference, sample Color) float64 {

// See

// https://github.com/w3c/csswg-drafts/issues/6642#issuecomment-945714988

// and

// https://github.com/color-js/color.js/blob/40e7a059c639bafde14504627e62791588c63100/src/deltaE/deltaEOK2.js

// for background on the scaling.

ref := reference.Convert(Oklab)

s := sample.Convert(Oklab)

Δ0 := ref.Values[0] - s.Values[0]

Δ1 := 2 * (ref.Values[1] - s.Values[1])

Δ2 := 2 * (ref.Values[2] - s.Values[2])

return math.Hypot(math.Hypot(Δ0, Δ1), Δ2)

}