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ICC: Add Profile::to_lab()
This can be used to convert a profile-dependent color to the L*a*b* color space. (I'd like to use this to implement the DeltaE (CIE 2000) algorithm, which is a metric for how similar two colors are perceived. (And I'd like to use that to evaluate color conversion roundtrip quality, once I've implemented full conversions.)
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@ -153,3 +153,53 @@ TEST_CASE(to_pcs)
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float f192 = sRGB_curve.evaluate(192 / 255.f);
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EXPECT_APPROXIMATE_VECTOR3(xyz_from_sRGB(64, 128, 192), r_xyz * f64 + g_xyz * f128 + b_xyz * f192);
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}
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TEST_CASE(to_lab)
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{
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auto sRGB = MUST(Gfx::ICC::sRGB());
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auto lab_from_sRGB = [sRGB](u8 r, u8 g, u8 b) {
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u8 rgb[3] = { r, g, b };
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return MUST(sRGB->to_lab(rgb));
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};
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// The `expected` numbers are from https://colorjs.io/notebook/ for this snippet of code:
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// new Color("srgb", [0, 0, 0]).lab.toString();
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//
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// new Color("srgb", [1, 0, 0]).lab.toString();
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// new Color("srgb", [0, 1, 0]).lab.toString();
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// new Color("srgb", [0, 0, 1]).lab.toString();
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//
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// new Color("srgb", [1, 1, 0]).lab.toString();
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// new Color("srgb", [1, 0, 1]).lab.toString();
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// new Color("srgb", [0, 1, 1]).lab.toString();
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//
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// new Color("srgb", [1, 1, 1]).lab.toString();
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Gfx::ICC::Profile::CIELAB expected[] = {
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{ 0, 0, 0 },
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{ 54.29054294696968, 80.80492033462421, 69.89098825896275 },
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{ 87.81853633115202, -79.27108223854806, 80.99459785152247 },
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{ 29.56829715344471, 68.28740665215547, -112.02971798617645 },
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{ 97.60701009682253, -15.749846639252663, 93.39361164266089 },
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{ 60.16894098715946, 93.53959546199253, -60.50080231921204 },
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{ 90.66601315791455, -50.65651077286893, -14.961666625736525 },
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{ 100.00000139649632, -0.000007807961277528364, 0.000006766250648659877 },
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};
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// We're off by more than the default EXPECT_APPROXIMATE() error, so use EXPECT_APPROXIMATE_WITH_ERROR().
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// The difference is not too bad: ranges for L*, a*, b* are [0, 100], [-125, 125], [-125, 125],
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// so this is an error of considerably less than 0.1 for u8 channels.
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#define EXPECT_APPROXIMATE_LAB(l1, l2) \
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EXPECT_APPROXIMATE_WITH_ERROR((l1).L, (l2).L, 0.01); \
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EXPECT_APPROXIMATE_WITH_ERROR((l1).a, (l2).a, 0.03); \
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EXPECT_APPROXIMATE_WITH_ERROR((l1).b, (l2).b, 0.02);
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EXPECT_APPROXIMATE_LAB(lab_from_sRGB(0, 0, 0), expected[0]);
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EXPECT_APPROXIMATE_LAB(lab_from_sRGB(255, 0, 0), expected[1]);
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EXPECT_APPROXIMATE_LAB(lab_from_sRGB(0, 255, 0), expected[2]);
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EXPECT_APPROXIMATE_LAB(lab_from_sRGB(0, 0, 255), expected[3]);
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EXPECT_APPROXIMATE_LAB(lab_from_sRGB(255, 255, 0), expected[4]);
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EXPECT_APPROXIMATE_LAB(lab_from_sRGB(255, 0, 255), expected[5]);
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EXPECT_APPROXIMATE_LAB(lab_from_sRGB(0, 255, 255), expected[6]);
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EXPECT_APPROXIMATE_LAB(lab_from_sRGB(255, 255, 255), expected[7]);
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}
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