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LibGfx/ICC: Implement conversion to PCS for AToB*Tags using mAB

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...as long as the mAB tag doesn't have A curves and a CLUT.

With this, we can convert images that use AToB* tags to the profile
connection space (and then from there to, say, sRGB), if the AToB* tag
uses the mAB format.

We can't yet do this if the mAB tag has A curves or a CLUT.

We can't convert back from PCS to this space yet.

We don't yet handle AToB* tags that use mft1 or mft2 instead of mAB.
This commit is contained in:
Nico Weber 2023-10-20 08:42:32 -04:00 • committed by Andreas Kling
parent 15bddf5de3
commit c25538b2e3
2 changed files with 82 additions and 4 deletions
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18
Userland/Libraries/LibGfx/ICC/Profile.cpp
View file

@ -1374,8 +1374,11 @@ static TagSignature forward_transform_tag_for_rendering_intent(RenderingIntent r
VERIFY_NOT_REACHED();
}
ErrorOr<FloatVector3> Profile::to_pcs_a_to_b(TagData const& tag_data, ReadonlyBytes) const
ErrorOr<FloatVector3> Profile::to_pcs_a_to_b(TagData const& tag_data, ReadonlyBytes color) const
{
// Assumes a "normal" device_class() (i.e. not DeviceLink).
VERIFY(number_of_components_in_color_space(connection_space()) == 3);
switch (tag_data.type()) {
case Lut16TagData::Type:
// FIXME
@ -1383,9 +1386,16 @@ ErrorOr<FloatVector3> Profile::to_pcs_a_to_b(TagData const& tag_data, ReadonlyBy
case Lut8TagData::Type:
// FIXME
return Error::from_string_literal("ICC::Profile::to_pcs: AToB*Tag handling for mft1 tags not yet implemented");
case LutAToBTagData::Type:
// FIXME
return Error::from_string_literal("ICC::Profile::to_pcs: AToB*Tag handling for mAB tags not yet implemented");
case LutAToBTagData::Type: {
auto const& a_to_b = static_cast<LutAToBTagData const&>(tag_data);
if (a_to_b.number_of_input_channels() != number_of_components_in_color_space(data_color_space()))
return Error::from_string_literal("ICC::Profile::to_pcs_a_to_b: mAB input channel count does not match color space size");
if (a_to_b.number_of_output_channels() != number_of_components_in_color_space(connection_space()))
return Error::from_string_literal("ICC::Profile::to_pcs_a_to_b: mAB output channel count does not match profile connection space size");
return a_to_b.evaluate(color);
}
}
VERIFY_NOT_REACHED();
}

68
Userland/Libraries/LibGfx/ICC/TagTypes.h
View file

@ -13,6 +13,7 @@
#include <AK/String.h>
#include <AK/Vector.h>
#include <LibGfx/ICC/DistinctFourCC.h>
#include <LibGfx/Vector3.h>
#include <math.h>
namespace Gfx::ICC {
@ -411,6 +412,9 @@ public:
Optional<EMatrix3x4> const& e_matrix() const { return m_e; }
Vector<LutCurveType> const& b_curves() const { return m_b_curves; }
// Returns the result of the LUT pipeline for u8 inputs.
ErrorOr<FloatVector3> evaluate(ReadonlyBytes) const;
private:
u8 m_number_of_input_channels;
u8 m_number_of_output_channels;
@ -984,6 +988,70 @@ private:
Vector<XYZ, 1> m_xyzs;
};
inline ErrorOr<FloatVector3> LutAToBTagData::evaluate(ReadonlyBytes color_u8) const
{
VERIFY(number_of_input_channels() == color_u8.size());
VERIFY(number_of_output_channels() == 3);
// ICC v4, 10.12 lutAToBType
// "Data are processed using these elements via the following sequence:
// (“A” curves) ⇨ (multi-dimensional lookup table, CLUT) ⇨ (“M” curves) ⇨ (matrix) ⇨ (“B” curves).
auto evaluate_curve = [](LutCurveType const& curve, float f) {
VERIFY(curve->type() == CurveTagData::Type || curve->type() == ParametricCurveTagData::Type);
if (curve->type() == CurveTagData::Type)
return static_cast<CurveTagData const&>(*curve).evaluate(f);
return static_cast<ParametricCurveTagData const&>(*curve).evaluate(f);
};
VERIFY(m_a_curves.has_value() == m_clut.has_value());
if (m_a_curves.has_value()) {
// FIXME
return Error::from_string_literal("mAB evaluation not yet implemented for A curve and CLUT");
}
FloatVector3 color { color_u8[0] / 255.f, color_u8[1] / 255.f, color_u8[2] / 255.f };
VERIFY(m_m_curves.has_value() == m_e.has_value());
if (m_m_curves.has_value()) {
auto const& m_curves = m_m_curves.value();
color = FloatVector3 {
evaluate_curve(m_curves[0], color[0]),
evaluate_curve(m_curves[1], color[1]),
evaluate_curve(m_curves[2], color[2])
};
// ICC v4, 10.12.5 Matrix
// "The resultant values Y1, Y2 and Y3 shall be clipped to the range 0,0 to 1,0 and used as inputs to the “B” curves."
EMatrix3x4 const& e = m_e.value();
FloatVector3 new_color = {
(float)e[0] * color[0] + (float)e[1] * color[1] + (float)e[2] * color[2] + (float)e[9],
(float)e[3] * color[0] + (float)e[4] * color[1] + (float)e[5] * color[2] + (float)e[10],
(float)e[6] * color[0] + (float)e[7] * color[1] + (float)e[8] * color[2] + (float)e[11]
};
// Mystery conversion factor!
// skcms, littlecms, and argyll all do this somewhere, but I don't understand why!
// skcms has a "TODO: understand" comment as well.
// littlecms and argyll have both comments which don't make sense to me.
// littlecms does this to the matrix profile matrices (i.e. it considers the lut pcs scale canonical).
// skcms does it to the mAB matrix (...which means it'll do something different if the matrix is missing,
// and it'll also do something different if the b curve isn't the identity).
// argyll does it in Lut_Lut2XYZ(), but I'm not clear on when that's called.
// SampleICC does it in IccCmm.cpp, XYZScale() and in IccUtil.cpp, icXyzFromPcs().
// Without this, colors are too bright. So let's do it too, and maybe I'll understand it one day.
new_color *= 65535 / 32768.f; // ???
color = new_color.clamped(0.f, 1.f);
}
return FloatVector3 {
evaluate_curve(m_b_curves[0], color[0]),
evaluate_curve(m_b_curves[1], color[1]),
evaluate_curve(m_b_curves[2], color[2])
};
}
}
template<>