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ICC: Implement TRC inversion in from_pcs for parametric curves

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Nico Weber 2023-05-01 11:14:10 -04:00 • committed by Sam Atkins
parent 4169c94ebe
commit 9bd35fda56
3 changed files with 71 additions and 8 deletions
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25
Userland/Libraries/LibGfx/ICC/Profile.cpp
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@ -1551,6 +1551,7 @@ ErrorOr<void> Profile::from_pcs(FloatVector3 const& pcs, Bytes color) const
// greenTRC^-1, and blueTRC^-1 function is undefined. If a one-dimensional curve is constant, the curve cannot be
// inverted."
// Convert from XYZ to linear rgb.
// FIXME: Inverting matrix and curve on every call to this function is very inefficient.
auto const& red_matrix_column = this->red_matrix_column();
auto const& green_matrix_column = this->green_matrix_column();
@ -1561,13 +1562,22 @@ ErrorOr<void> Profile::from_pcs(FloatVector3 const& pcs, Bytes color) const
red_matrix_column.Y, green_matrix_column.Y, blue_matrix_column.Y,
red_matrix_column.Z, green_matrix_column.Z, blue_matrix_column.Z
};
if (!forward_matrix.is_invertible())
return Error::from_string_literal("ICC::Profile::from_pcs: matrix not invertible");
auto matrix = forward_matrix.inverse();
FloatVector3 linear_rgb = matrix * pcs;
auto evaluate_curve_inverse = [this](TagSignature curve_tag, float f) {
auto const& trc = *m_tag_table.get(curve_tag).value();
VERIFY(trc.type() == CurveTagData::Type || trc.type() == ParametricCurveTagData::Type);
if (trc.type() == CurveTagData::Type) {
TODO();
return 0.f;
}
return static_cast<ParametricCurveTagData const&>(trc).evaluate_inverse(f);
};
// Convert from linear rgb to device rgb.
// See equations (F.8) - (F.16) above.
// FIXME: The spec says to do this, but it loses information. Color.js returns unclamped
// values instead (...but how do those make it through the TRC?) and has a separate
@ -1576,12 +1586,13 @@ ErrorOr<void> Profile::from_pcs(FloatVector3 const& pcs, Bytes color) const
// (For LUT profiles, I think the gamut mapping is baked into the BToA* data in the profile (?).
// But for matrix profiles, it'd have to be done in code.)
linear_rgb.clamp(0.f, 1.f);
float device_r = evaluate_curve_inverse(redTRCTag, linear_rgb[0]);
float device_g = evaluate_curve_inverse(greenTRCTag, linear_rgb[1]);
float device_b = evaluate_curve_inverse(blueTRCTag, linear_rgb[2]);
// FIXME: Implement curve inversion and apply inverse curve transform here.
color[0] = round(255 * linear_rgb[0]);
color[1] = round(255 * linear_rgb[1]);
color[2] = round(255 * linear_rgb[2]);
color[0] = round(255 * device_r);
color[1] = round(255 * device_g);
color[2] = round(255 * device_b);
return {};
}