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ICC: Implement TRC inversion in from_pcs for parametric curves
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3 changed files with 71 additions and 8 deletions
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@ -158,6 +158,10 @@ TEST_CASE(from_pcs)
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{
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auto sRGB = MUST(Gfx::ICC::sRGB());
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auto sRGB_curve_pointer = MUST(Gfx::ICC::sRGB_curve());
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VERIFY(sRGB_curve_pointer->type() == Gfx::ICC::ParametricCurveTagData::Type);
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auto const& sRGB_curve = static_cast<Gfx::ICC::ParametricCurveTagData const&>(*sRGB_curve_pointer);
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auto sRGB_from_xyz = [&sRGB](FloatVector3 const& XYZ) {
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u8 rgb[3];
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MUST(sRGB->from_pcs(XYZ, rgb));
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@ -185,7 +189,16 @@ TEST_CASE(from_pcs)
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EXPECT_EQ(sRGB_from_xyz(g_xyz + b_xyz), Color(0, 255, 255));
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EXPECT_EQ(sRGB_from_xyz(r_xyz + g_xyz + b_xyz), Color(255, 255, 255));
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// FIXME: Implement and test the inverse curve transform.
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// Test the inverse curve transform.
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float f64 = sRGB_curve.evaluate(64 / 255.f);
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EXPECT_EQ(sRGB_from_xyz((r_xyz + g_xyz + b_xyz) * f64), Color(64, 64, 64));
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float f128 = sRGB_curve.evaluate(128 / 255.f);
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EXPECT_EQ(sRGB_from_xyz((r_xyz + g_xyz + b_xyz) * f128), Color(128, 128, 128));
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// Test for curve and matrix combined.
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float f192 = sRGB_curve.evaluate(192 / 255.f);
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EXPECT_EQ(sRGB_from_xyz(r_xyz * f64 + g_xyz * f128 + b_xyz * f192), Color(64, 128, 192));
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}
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TEST_CASE(to_lab)
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@ -1551,6 +1551,7 @@ ErrorOr<void> Profile::from_pcs(FloatVector3 const& pcs, Bytes color) const
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// greenTRC^-1, and blueTRC^-1 function is undefined. If a one-dimensional curve is constant, the curve cannot be
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// inverted."
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// Convert from XYZ to linear rgb.
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// FIXME: Inverting matrix and curve on every call to this function is very inefficient.
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auto const& red_matrix_column = this->red_matrix_column();
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auto const& green_matrix_column = this->green_matrix_column();
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@ -1561,13 +1562,22 @@ ErrorOr<void> Profile::from_pcs(FloatVector3 const& pcs, Bytes color) const
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red_matrix_column.Y, green_matrix_column.Y, blue_matrix_column.Y,
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red_matrix_column.Z, green_matrix_column.Z, blue_matrix_column.Z
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};
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if (!forward_matrix.is_invertible())
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return Error::from_string_literal("ICC::Profile::from_pcs: matrix not invertible");
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auto matrix = forward_matrix.inverse();
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FloatVector3 linear_rgb = matrix * pcs;
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auto evaluate_curve_inverse = [this](TagSignature curve_tag, float f) {
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auto const& trc = *m_tag_table.get(curve_tag).value();
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VERIFY(trc.type() == CurveTagData::Type || trc.type() == ParametricCurveTagData::Type);
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if (trc.type() == CurveTagData::Type) {
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TODO();
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return 0.f;
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}
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return static_cast<ParametricCurveTagData const&>(trc).evaluate_inverse(f);
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};
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// Convert from linear rgb to device rgb.
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// See equations (F.8) - (F.16) above.
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// FIXME: The spec says to do this, but it loses information. Color.js returns unclamped
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// values instead (...but how do those make it through the TRC?) and has a separate
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@ -1576,12 +1586,13 @@ ErrorOr<void> Profile::from_pcs(FloatVector3 const& pcs, Bytes color) const
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// (For LUT profiles, I think the gamut mapping is baked into the BToA* data in the profile (?).
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// But for matrix profiles, it'd have to be done in code.)
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linear_rgb.clamp(0.f, 1.f);
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float device_r = evaluate_curve_inverse(redTRCTag, linear_rgb[0]);
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float device_g = evaluate_curve_inverse(greenTRCTag, linear_rgb[1]);
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float device_b = evaluate_curve_inverse(blueTRCTag, linear_rgb[2]);
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// FIXME: Implement curve inversion and apply inverse curve transform here.
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color[0] = round(255 * linear_rgb[0]);
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color[1] = round(255 * linear_rgb[1]);
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color[2] = round(255 * linear_rgb[2]);
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color[0] = round(255 * device_r);
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color[1] = round(255 * device_g);
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color[2] = round(255 * device_b);
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return {};
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}
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@ -739,6 +739,45 @@ public:
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VERIFY_NOT_REACHED();
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}
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// y must be in [0..1].
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float evaluate_inverse(float y) const
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{
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VERIFY(0.f <= y && y <= 1.f);
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// See "Recommendations" section in https://www.color.org/whitepapers/ICC_White_Paper35-Use_of_the_parametricCurveType.pdf
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// Requirements for the curve to be non-decreasing:
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// * γ > 0
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// * a > 0 for types 1-4
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// * c ≥ 0 for types 3 and 4
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//
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// Types 3 and 4 additionally require:
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// To prevent negative discontinuities:
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// * cd ≤ (ad + b) for type 3
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// * cd + f ≤ (ad + b)^γ + e for type 4
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// To prevent complex numbers:
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// * ad + b ≥ 0
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// FIXME: Check these requirements somewhere.
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switch (function_type()) {
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case FunctionType::Type0:
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return powf(y, 1.f / (float)g());
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case FunctionType::Type1:
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return (powf(y, 1.f / (float)g()) - (float)b()) / (float)a();
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case FunctionType::Type2:
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// Only defined for Y >= c, so I suppose this requires c <= 0 in practice (?).
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return (powf(y - (float)c(), 1.f / (float)g()) - (float)b()) / (float)a();
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case FunctionType::Type3:
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if (y >= (float)c() * (float)d())
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return (powf(y, 1.f / (float)g()) - (float)b()) / (float)a();
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return y / (float)c();
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case FunctionType::Type4:
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if (y >= (float)c() * (float)d())
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return (powf(y - (float)e(), 1.f / (float)g()) - (float)b()) / (float)a();
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return (y - (float)f()) / (float)c();
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}
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VERIFY_NOT_REACHED();
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}
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private:
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FunctionType m_function_type;
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