This repository was archived by the owner on Apr 1, 2026. It is now read-only.
Repository navigation
Expand file tree
/
Copy pathcolor.go
More file actions
389 lines (362 loc) · 12.6 KB
/
Copy pathcolor.go
File metadata and controls
389 lines (362 loc) · 12.6 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
// See https://github.com/w3c/csswg-drafts/issues/6618 for a discussion on the
// specific white points used in the CSS Color Module Level 4 spec. tl;dr: there
// are a dozen different definitions of D65, we have to pick one. Same for D50.
// Useful links:
// - https://facelessuser.github.io/coloraide/
// - https://colorjs.io/
// - https://www.w3.org/TR/css-color-4
// Package color provides types and functions for working with colors.
//
// # Color
//
// The core type is [Color], a color space-aware type for representing colors in
// any 3-axis coordinate system. For example, one color may be represented in a
// cartesian sRGB color space, while another is represented in the cylindrical
// Oklch. Colors can be instantiated directly or created with the [Make]
// helper. Additionally, the CSS 'color()' syntax is supported and can be parsed
// by [Parse]. The package provides numerous color spaces, as variables of
// type [Space].
//
// Colors can be freely converted between any two color spaces, with optional
// gamut mapping. To convert a Color without gamut mapping, use [Color.Convert].
// If the destination color space is narrower than the source space (for
// example, when converting from Display P3 to sRGB), the new Color might not be
// in gamut and have values outside the expected range. Package color does not
// apply gamut mapping automatically for two reasons:
//
// 1. No gamut mapping approach is perfect and we leave the choice of which
// algorithm to use up to the user.
//
// 2. Automatic gamut mapping would prevent colors from being roundtrippable.
// Without gamut mapping, it is possible to go from a wider to a narrower and
// back to a wider color space without losing information (except for the
// introduction of rounding errors).
//
// A decent gamut mapping operation with a relative colorimetric intent is
// implemented by [GamutMapCSS]. This is the same algorithm that is used by
// browsers that implement the [CSS Color Module Level 4] standard.
//
// Whether a color is in gamut for its color space can be checked with
// [Color.InGamut]. There is also [Color.InGamutOf] that checks if a color, when
// converted to a target color space, will be in gamut.
//
// The following example shows the creation of a very saturated pink (more
// saturated than can be displayed by non-wide-gamut displays) using Oklch and
// its conversion to sRGB with and without gamut mapping.
//
// veryPink := Make(Oklch, 0.65, 0.29, 0, 1)
// pinkSRGB := GamutMapCSS(veryPink, SRGB)
// veryPinkSRGB := veryPink.Convert(SRGB)
//
// fmt.Println(veryPink, veryPink.InGamut())
// fmt.Println(pinkSRGB, pinkSRGB.InGamut())
// fmt.Println(veryPinkSRGB, veryPinkSRGB.InGamut())
//
// Output:
//
// color(--oklch 0.650000 0.290000 0.000000) true
// color(srgb 1.000000 0.000000 0.533824) true
// color(srgb 1.040595 -0.191616 0.533106) false
//
// This is everything that is needed to create and use colors. The following
// sections describe more advanced but optional functionality.
//
// # Color spaces
//
// Without an associated color space, a triple like (0.6, 0.2, 0) conveys no
// meaning. It might represent a brown color in sRGB (when representing values
// as floating point values in the range [0, 1]), or a soft pink in Oklch.
//
// Package color supports numerous color spaces and allows users to define their
// own. They are represented by the [Space] type. Color spaces include meta
// data such as an ID (for use with [Parse]) and name as well as a
// [white point]. However, their main functionality is provided by having a
// "base" color space to and from which a color space can be converted. The base
// space might be closely related, such as sRGB being based on linear sRGB (as
// the former is just the latter with a transfer function applied). It might
// also be a more fundamental color space, often XYZ with the appropriate white
// point. Together, all color spaces form a tree, with XYZ D65 as the root. This
// tree allows converting between any two color spaces by finding a common
// ancestor (the conversion space) and applying a series of conversions from the
// source space to the conversion space and from the conversion space to the
// target space.
//
// # Chromatic adaptation
//
// Different color spaces may have different white points, requiring [chromatic
// adaptation] when converting between them. This is automatically handled
// during color space conversion. Every color space's chain of base spaces will
// eventually lead to an XYZ color space with the appropriate white point. When
// converting between two XYZ color spaces with different white points, we use
// the Bradford method to adapt between them.
//
// It is also possible to manually apply chromatic adaptation using the [CAT]
// type. This package provides the [Bradford] and [CAT16] transformations, but
// any transformation that is based on using a 3x3 matrix to map to a cone
// response and another 3x3 matrix to map from a cone response can be
// implemented using [CAT].
//
// Furthermore, we provide definitions for numerous white points, expressed as
// xy chromaticities using the [Chromaticity] type. Additionally, CIE daylight
// illuminants can be created with [MakeCIEDaylightIlluminant].
//
// New XYZ spaces with custom white points can be created with [NewXYZSpace].
//
// # Other functionality
//
// The perceptual difference between two colors can be computed by functions
// whose names start with "Delta", such as [DeltaEOK2]. Different functions have
// different tradeoffs.
//
// The contrast of two colors can be computed by functions whose names start
// with "Contrast", such as [ContrastWeber]. Different functions have different
// tradeoffs.
//
// [Step] creates color gradients by linearly interpolating between two colors
// in a color space of your choice.
//
// [CSS Color Module Level 4]: https://www.w3.org/TR/css-color-4/
// [white point]: https://en.wikipedia.org/wiki/White_point
// [chromatic adaptation]: https://en.wikipedia.org/wiki/Chromatic_adaptation
package color
// TODO(dh): https://github.com/WICG/color-api/issues/30
// a98rgb-linear.js
// a98rgb.js
// acescc.js
// acescg.js
// cam16.js
// hct.js
// hpluv.js
// hsl.js
// hsluv.js
// hsv.js
// hwb.js
// ictcp.js
// jzazbz.js
// jzczhz.js
// lab-d65.js
// lchuv.js
// luv.js
// okhsl.js
// okhsv.js
// oklrab.js
// oklrch.js
// rec2020-linear.js
// rec2020.js
// rec2100-hlg.js
// rec2100-pq.js
// xyz-abs-d65.js
import (
"fmt"
"iter"
)
// Make is a convenience function for initializing colors.
func Make(space *Space, p1, p2, p3, alpha float64) Color {
if alpha < 0 {
alpha = 0
} else if alpha > 1 {
alpha = 1
}
return Color{
Values: [4]float64{p1, p2, p3, alpha},
Space: space,
}
}
func lerp(x, y float64, a float64) float64 {
return x*(1.0-a) + y*a
}
// Step computes num colors that lie between c1 and c2, interpolating in the in
// color space and returning them in the out color space, without applying any
// gamut mapping.
func Step(c1, c2 Color, in, out *Space, num int) iter.Seq[Color] {
if num < 2 {
panic("need at least two steps")
}
return func(yield func(Color) bool) {
c1in := c1.Convert(in)
c2in := c2.Convert(in)
for i := range num {
t := float64(i) / float64(num-1)
c := Make(
in,
lerp(c1in.Values[0], c2in.Values[0], t),
lerp(c1in.Values[1], c2in.Values[1], t),
lerp(c1in.Values[2], c2in.Values[2], t),
lerp(c1in.Values[3], c2in.Values[3], t),
)
cout := c.Convert(out)
if !yield(cout) {
return
}
}
}
}
// Chromaticity describes a color's chromaticity in the CIE 1931 xy color space.
type Chromaticity struct {
X float64
Y float64
}
// XYZ converts the xy chromaticity to the X, Y, and Z tristimulus values, with
// Y = 1.
func (chr Chromaticity) XYZ() [3]float64 {
return [3]float64{
chr.X / chr.Y,
1,
(1 - chr.X - chr.Y) / chr.Y,
}
}
// Color represents a color with 3 coordinates in some color space, plus an
// alpha channel. The meaning of the first three values depends on the color
// space. The alpha value does not affect operations such as color space
// conversions, gamut mapping, or distance metrics and will simply be preserved.
// [Step], however, will interpolate between the start and end alpha values.
// Color values are not premultiplied by alpha.
//
// The values of a color may be out of gamut for the color space. This is
// allowed so that conversions between color spaces do not lose any information,
// even if the destination space is smaller than the source space. The package
// provides functions for explicit gamut mapping.
type Color struct {
Values [4]float64
Space *Space
}
func (c Color) String() string {
var isCSS bool
switch c.Space.ID {
case "srgb", "srgb-linear", "display-p3", "a98-rgb", "prophoto-rgb",
"rec2020", "xyz-d50", "xyz-d65":
isCSS = true
}
id := c.Space.ID
if !isCSS {
id = "--" + id
}
if c.Values[3] != 1 {
return fmt.Sprintf("color(%s %f %f %f / %f)",
id, c.Values[0], c.Values[1], c.Values[2], c.Values[3])
} else {
return fmt.Sprintf("color(%s %f %f %f)",
id, c.Values[0], c.Values[1], c.Values[2])
}
}
// Convert converts c from its current color space to a different color space.
// It does not apply any gamut mapping.
func (c Color) Convert(space *Space) Color {
if c.Space == space {
return c
}
v := c.Space.Convert(space, [3]float64(c.Values[:]))
return Color{
Values: [4]float64{v[0], v[1], v[2], c.Values[3]},
Space: space,
}
}
// InGamut reports whether c's values are in gamut of its color space.
func (c Color) InGamut() bool {
return c.Space.InGamut([3]float64(c.Values[:]))
}
// InGamutOf reports whether c, when converted to space, is in gamut.
func (c Color) InGamutOf(space *Space) bool {
return c.Convert(space).InGamut()
}
// GamutMapCSS uses the [CSS gamut mapping algorithm] to map individual colors
// to a destination color space. It implements a relative colorimetric intent.
// That is, colors that are already inside the target gamut are unchanged. This
// is intended for mapping individual colors, not for mapping images.
//
// For some limitations of this algorithm, see [1] and [2].
//
// [CSS gamut mapping algorithm]: https://www.w3.org/TR/css-color-4/#css-gamut-mapping
// [1]: https://github.com/w3c/csswg-drafts/issues/7071
// [2]: https://github.com/w3c/csswg-drafts/issues/9449
func GamutMapCSS(c Color, to *Space) Color {
// 1. if destination has no gamut limits (XYZ-D65, XYZ-D50, Lab, LCH,
// Oklab, Oklch) convert origin to destination and return it as the
// gamut mapped color
if to.Coords[0].Range == infty &&
to.Coords[1].Range == infty &&
to.Coords[2].Range == infty {
return c.Convert(to)
}
cOklch := c.Convert(Oklch)
if cOklch.Values[0] >= 1 {
out := Make(Oklab, 1, 0, 0, c.Values[3])
return out.Convert(to)
}
if cOklch.Values[0] <= 0 {
out := Make(Oklab, 0, 0, 0, c.Values[3])
return out.Convert(to)
}
if out := cOklch.Convert(to); out.InGamut() {
return out
}
// The just noticeable difference between two colors in Oklch
const jnd = 0.02
const ϵ = 0.0001
clip := func(cc Color) Color {
clamp := func(f, low, high float64) float64 {
if f < low {
return low
}
if f > high {
return high
}
return f
}
ccc := cc.Convert(to)
ccc.Values[0] = clamp(ccc.Values[0], ccc.Space.Coords[0].Range[0], ccc.Space.Coords[0].Range[1])
ccc.Values[1] = clamp(ccc.Values[1], ccc.Space.Coords[1].Range[0], ccc.Space.Coords[1].Range[1])
ccc.Values[2] = clamp(ccc.Values[2], ccc.Space.Coords[2].Range[0], ccc.Space.Coords[2].Range[1])
return ccc
}
current := cOklch
clipped := clip(current)
e := DeltaEOK(clipped, current)
if e < jnd {
return clipped
}
min := 0.0
max := cOklch.Values[1]
minInGamut := true
for max-min > ϵ {
chroma := (min + max) / 2
current.Values[1] = chroma
if minInGamut && current.InGamutOf(to) {
min = chroma
continue
} else if !current.InGamutOf(to) {
clipped = clip(current)
e = DeltaEOK(clipped, current)
if e < jnd {
if jnd-e < ϵ {
return clipped
} else {
minInGamut = false
min = chroma
}
} else {
max = chroma
continue
}
}
}
return clipped
}
// Coordinate is metadata describing a coordinate of a color space.
type Coordinate struct {
// Name is the human readable name of the coordinate.
Name string
// Range describes the range of values that are in gamut. For some
// coordinates in some color spaces, this will be [-∞, ∞].
Range [2]float64
// RefRange describes the values that map to 0% and 100%. If not set, defaults
// to Range.
RefRange [2]float64
// IsAngle is true for coordinates that represent angles, such as color hue.
IsAngle bool
}
var RGBCoordinates = [3]Coordinate{
{Name: "Red", Range: [2]float64{0, 1}},
{Name: "Green", Range: [2]float64{0, 1}},
{Name: "Blue", Range: [2]float64{0, 1}},
}