104 lines
4.5 KiB
Go
104 lines
4.5 KiB
Go
package helper
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import (
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"image/color"
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"math"
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)
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func XYZtoLMS(x, y, z float64) (_, _, _ float64) {
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// https://bottosson.github.io/posts/oklab/
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//
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// OkLab first defines a transform from xyz to an intermediate space:
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//
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// [+0.8189330101, +0.3618667424, -0.1288597137]
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// [+0.0329845436, +0.9293118715, +0.0361456387]
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// [+0.0482003018, +0.2643662691, +0.633851707 ]
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//
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// Inverse:
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//
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// [+1.2270138511035210261251539010893, -0.55779998065182223833890733780747, +0.28125614896646780760667886762980 ]
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// [-0.040580178423280593980748617561551, +1.1122568696168301049956590765194, -0.071676678665601200581102747142872]
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// [-0.076381284505706892872271894590358, -0.42148197841801273056818761141308, +1.5861632204407947575338479416771 ]
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return +0.8189330101*x + 0.3618667424*y - 0.1288597137*z,
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0.0329845436*x + 0.9293118715*y + 0.0361456387*z,
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0.0482003018*x + 0.2643662691*y + 0.633851707*z
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}
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func LMStoXYZ(l, m, s float64) (_, _, _ float64) {
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return 1.2270138511035210261251539010893*l - 0.55779998065182223833890733780747*m + 0.28125614896646780760667886762980*s,
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-0.040580178423280593980748617561551*l + 1.1122568696168301049956590765194*m - 0.071676678665601200581102747142872*s,
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-0.076381284505706892872271894590358*l - 0.42148197841801273056818761141308*m + 1.5861632204407947575338479416771*s
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}
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func LRGBtoLMS(r, g, b float64) (_, _, _ float64) {
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// we can combine the LRGB to D65 CIE XYZ transform and the XYZ to LMS transform above to go straight from LRGB to LMS:
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//
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// [+0.41217385032507, +0.5362974607032, +0.05146302925248]
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// [+0.21187214048845, +0.6807476834212, +0.10740645682645]
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// [+0.08831541121808, +0.2818663070584, +0.63026344660742]
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//
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// Inverse:
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//
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// [+4.0767584135565013494237930518854, -3.3072279873944731418619352916485, +0.23072145994488563247301883404900]
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// [-1.2681810851624033989047813181437, +2.6092932102856398573991970933594, -0.34111211654775355696796160418220]
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// [-0.0040984077180314400491332639337372, -0.70350366010241732765095902557887, +1.7068604529788013559365593912662]
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return +0.41217385032507*r + 0.5362974607032*g + 0.05146302925248*b,
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0.21187214048845*r + 0.6807476834212*g + 0.10740645682645*b,
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0.08831541121808*r + 0.2818663070584*g + 0.63026344660742*b
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}
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func LMStoLRGB(l, m, s float64) (_, _, _ float64) {
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return +4.0767584135565013494237930518854*l - 3.3072279873944731418619352916485*m + 0.23072145994488563247301883404900*s,
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-1.2681810851624033989047813181437*l + 2.6092932102856398573991970933594*m - 0.34111211654775355696796160418220*s,
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-0.0040984077180314400491332639337372*l - 0.70350366010241732765095902557887*m + 1.7068604529788013559365593912662*s
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}
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func LMStoOkLab(l, m, s float64) (_, _, _ float64) {
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// After a non-linear transformation (cube root), OkLab applies a second matrix:
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//
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// [+0.2104542553, +0.793617785, -0.0040720468]
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// [+1.9779984951, -2.428592205, +0.4505937099]
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// [+0.0259040371, +0.7827717662, -0.808675766 ]
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//
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// Inverse:
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//
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// [+0.99999999845051981426207542502031, +0.39633779217376785682345989261573, +0.21580375806075880342314146183004 ]
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// [+1.0000000088817607767160752456705, -0.10556134232365634941095687705472, -0.063854174771705903405254198817796]
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// [+1.0000000546724109177012928651534, -0.089484182094965759689052745863391, -1.2914855378640917399489287529148 ]
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lP, mP, sP := math.Cbrt(l), math.Cbrt(m), math.Cbrt(s)
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return 0.2104542553*lP + 0.793617785*mP - 0.0040720468*sP,
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1.9779984951*lP - 2.428592205*mP + 0.4505937099*sP,
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0.0259040371*lP + 0.7827717662*mP - 0.808675766*sP
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}
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func cube(v float64) float64 {
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return v * v * v
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}
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func OkLabToLMS(l, a, b float64) (_, _, _ float64) {
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return cube(0.99999999845051981426207542502031*l + 0.39633779217376785682345989261573*a + 0.21580375806075880342314146183004*b),
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cube(1.0000000088817607767160752456705*l - 0.10556134232365634941095687705472*a - 0.063854174771705903405254198817796*b),
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cube(1.0000000546724109177012928651534*l - 0.089484182094965759689052745863391*a - 1.2914855378640917399489287529148*b)
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}
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func ColorToNOkLabA(c color.Color) (lightness, chromaA, chromaB, a float64) {
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switch c := c.(type) {
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case interface {
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NOkLabA() (lightness, chromaA, chromaB, a float64)
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}:
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return c.NOkLabA()
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case interface{ NXYZA() (x, y, z, a float64) }:
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x, y, z, a := c.NXYZA()
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lightness, chromaA, chromaB = LMStoOkLab(XYZtoLMS(x, y, z))
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return lightness, chromaA, chromaB, a
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default:
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r, g, b, a := ColorToNLRGBA(c)
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lightness, chromaA, chromaB = LMStoOkLab(LRGBtoLMS(r, g, b))
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return lightness, chromaA, chromaB, a
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}
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}
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