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
|
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
// We are going to be doing so, so many transforms, so descriptive labels are
// critical.
#include "Colorspaces.h"
namespace mozilla::color {
// tf = { k * linear | linear < b
// { a * pow(linear, 1/g) - (1-a) | linear >= b
float TfFromLinear(const PiecewiseGammaDesc& desc, const float linear) {
if (linear < desc.b) {
return linear * desc.k;
}
float ret = linear;
ret = powf(ret, 1.0f / desc.g);
ret *= desc.a;
ret -= (desc.a - 1);
return ret;
}
float LinearFromTf(const PiecewiseGammaDesc& desc, const float tf) {
const auto linear_if_low = tf / desc.k;
if (linear_if_low < desc.b) {
return linear_if_low;
}
float ret = tf;
ret += (desc.a - 1);
ret /= desc.a;
ret = powf(ret, 1.0f * desc.g);
return ret;
}
// -
mat3 YuvFromRgb(const YuvLumaCoeffs& yc) {
// Y is always [0,1]
// U and V are signed, and could be either [-1,+1] or [-0.5,+0.5].
// Specs generally use [-0.5,+0.5], so we use that too.
// E.g.
// y = 0.2126*r + 0.7152*g + 0.0722*b
// u = (b - y) / (u_range = u_max - u_min) // u_min = -u_max
// = (b - y) / (u(0,0,1) - u(1,1,0))
// = (b - y) / (2 * u(0,0,1))
// = (b - y) / (2 * u.b))
// = (b - y) / (2 * (1 - 0.0722))
// = (-0.2126*r + -0.7152*g + (1-0.0722)*b) / 1.8556
// v = (r - y) / 1.5748;
// = ((1-0.2126)*r + -0.7152*g + -0.0722*b) / 1.5748
const auto y = vec3({yc.r, yc.g, yc.b});
const auto u = vec3({0, 0, 1}) - y;
const auto v = vec3({1, 0, 0}) - y;
// From rows:
return mat3({y, u / (2 * u.z()), v / (2 * v.x())});
}
mat4 YuvFromYcbcr(const YcbcrDesc& d) {
// E.g.
// y = (yy - 16) / (235 - 16); // 16->0, 235->1
// u = (cb - 128) / (240 - 16); // 16->-0.5, 128->0, 240->+0.5
// v = (cr - 128) / (240 - 16);
const auto yRange = d.y1 - d.y0;
const auto uHalfRange = d.uPlusHalf - d.u0;
const auto uRange = 2 * uHalfRange;
const auto ycbcrFromYuv = mat4{{vec4{{yRange, 0, 0, d.y0}},
{{0, uRange, 0, d.u0}},
{{0, 0, uRange, d.u0}},
{{0, 0, 0, 1}}}};
const auto yuvFromYcbcr = inverse(ycbcrFromYuv);
return yuvFromYcbcr;
}
mat3 XyzFromLinearRgb(const Chromaticities& c) {
// http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html
// Given red (xr, yr), green (xg, yg), blue (xb, yb),
// and whitepoint (XW, YW, ZW)
// [ X ] [ R ]
// [ Y ] = M x [ G ]
// [ Z ] [ B ]
// [ Sr*Xr Sg*Xg Sb*Xb ]
// M = [ Sr*Yr Sg*Yg Sb*Yb ]
// [ Sr*Zr Sg*Zg Sb*Zb ]
// Xr = xr / yr
// Yr = 1
// Zr = (1 - xr - yr) / yr
// Xg = xg / yg
// Yg = 1
// Zg = (1 - xg - yg) / yg
// Xb = xb / yb
// Yb = 1
// Zb = (1 - xb - yb) / yb
// [ Sr ] [ Xr Xg Xb ]^-1 [ XW ]
// [ Sg ] = [ Yr Yg Yb ] x [ YW ]
// [ Sb ] [ Zr Zg Zb ] [ ZW ]
const auto xrgb = vec3({c.rx, c.gx, c.bx});
const auto yrgb = vec3({c.ry, c.gy, c.by});
const auto Xrgb = xrgb / yrgb;
const auto Yrgb = vec3(1);
const auto Zrgb = (vec3(1) - xrgb - yrgb) / yrgb;
const auto XYZrgb = mat3({Xrgb, Yrgb, Zrgb});
const auto XYZrgb_inv = inverse(XYZrgb);
const auto XYZwhitepoint = vec3({c.wx, c.wy, 1 - c.wx - c.wy});
const auto Srgb = XYZrgb_inv * XYZwhitepoint;
const auto M = mat3({Srgb * Xrgb, Srgb * Yrgb, Srgb * Zrgb});
return M;
}
// -
ColorspaceTransform ColorspaceTransform::Create(const ColorspaceDesc& src,
const ColorspaceDesc& dst) {
auto ct = ColorspaceTransform{src, dst};
ct.srcTf = src.tf;
ct.dstTf = dst.tf;
const auto RgbTfFrom = [&](const ColorspaceDesc& cs) {
auto rgbFrom = mat4::Identity();
if (cs.yuv) {
const auto yuvFromYcbcr = YuvFromYcbcr(cs.yuv->ycbcr);
const auto yuvFromRgb = YuvFromRgb(cs.yuv->yCoeffs);
const auto rgbFromYuv = inverse(yuvFromRgb);
const auto rgbFromYuv4 = mat4(rgbFromYuv);
const auto rgbFromYcbcr = rgbFromYuv4 * yuvFromYcbcr;
rgbFrom = rgbFromYcbcr;
}
return rgbFrom;
};
ct.srcRgbTfFromSrc = RgbTfFrom(src);
const auto dstRgbTfFromDst = RgbTfFrom(dst);
ct.dstFromDstRgbTf = inverse(dstRgbTfFromDst);
// -
ct.dstRgbLinFromSrcRgbLin = mat3::Identity();
if (!(src.chrom == dst.chrom)) {
const auto xyzFromSrcRgbLin = XyzFromLinearRgb(src.chrom);
const auto xyzFromDstRgbLin = XyzFromLinearRgb(dst.chrom);
const auto dstRgbLinFromXyz = inverse(xyzFromDstRgbLin);
ct.dstRgbLinFromSrcRgbLin = dstRgbLinFromXyz * xyzFromSrcRgbLin;
}
return ct;
}
vec3 ColorspaceTransform::DstFromSrc(const vec3 src) const {
const auto srcRgbTf = srcRgbTfFromSrc * vec4(src, 1);
auto srcRgbLin = srcRgbTf;
if (srcTf) {
srcRgbLin.x(LinearFromTf(*srcTf, srcRgbTf.x()));
srcRgbLin.y(LinearFromTf(*srcTf, srcRgbTf.y()));
srcRgbLin.z(LinearFromTf(*srcTf, srcRgbTf.z()));
}
const auto dstRgbLin = dstRgbLinFromSrcRgbLin * vec3(srcRgbLin);
auto dstRgbTf = dstRgbLin;
if (dstTf) {
dstRgbTf.x(TfFromLinear(*dstTf, dstRgbLin.x()));
dstRgbTf.y(TfFromLinear(*dstTf, dstRgbLin.y()));
dstRgbTf.z(TfFromLinear(*dstTf, dstRgbLin.z()));
}
const auto dst4 = dstFromDstRgbTf * vec4(dstRgbTf, 1);
return vec3(dst4);
}
// -
std::optional<mat4> ColorspaceTransform::ToMat4() const {
mat4 fromSrc = srcRgbTfFromSrc;
if (srcTf) return {};
fromSrc = mat4(dstRgbLinFromSrcRgbLin) * fromSrc;
if (dstTf) return {};
fromSrc = dstFromDstRgbTf * fromSrc;
return fromSrc;
}
Lut3 ColorspaceTransform::ToLut3(const ivec3 size) const {
auto lut = Lut3::Create(size);
lut.SetMap([&](const vec3& srcVal) { return DstFromSrc(srcVal); });
return lut;
}
vec3 Lut3::Sample(const vec3 in01) const {
const auto coord = vec3(size - 1) * in01;
const auto p0 = floor(coord);
const auto dp = coord - p0;
const auto ip0 = ivec3(p0);
// Trilinear
const auto f000 = Fetch(ip0 + ivec3({0, 0, 0}));
const auto f100 = Fetch(ip0 + ivec3({1, 0, 0}));
const auto f010 = Fetch(ip0 + ivec3({0, 1, 0}));
const auto f110 = Fetch(ip0 + ivec3({1, 1, 0}));
const auto f001 = Fetch(ip0 + ivec3({0, 0, 1}));
const auto f101 = Fetch(ip0 + ivec3({1, 0, 1}));
const auto f011 = Fetch(ip0 + ivec3({0, 1, 1}));
const auto f111 = Fetch(ip0 + ivec3({1, 1, 1}));
const auto fx00 = mix(f000, f100, dp.x());
const auto fx10 = mix(f010, f110, dp.x());
const auto fx01 = mix(f001, f101, dp.x());
const auto fx11 = mix(f011, f111, dp.x());
const auto fxy0 = mix(fx00, fx10, dp.y());
const auto fxy1 = mix(fx01, fx11, dp.y());
const auto fxyz = mix(fxy0, fxy1, dp.z());
return fxyz;
}
} // namespace mozilla::color
|
