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LibGfx/ICC: Extract a lab_from_xyz() function

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Pure code move, no behavior change.
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Nico Weber 2023-12-03 21:29:35 -05:00 • committed by Sam Atkins
parent fda9840f48
commit 9f7b33c31f
1 changed files with 47 additions and 40 deletions
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87
Userland/Libraries/LibGfx/ICC/Profile.cpp
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@ -1331,6 +1331,51 @@ ErrorOr<FloatVector3> Profile::to_pcs(ReadonlyBytes color) const
VERIFY_NOT_REACHED(); VERIFY_NOT_REACHED();
} }
static FloatVector3 lab_from_xyz(FloatVector3 xyz, XYZ white_point)
{
// 6.3.2.2 Translation between media-relative colorimetric data and ICC-absolute colorimetric data
// 6.3.2.3 Computation of PCSLAB
// 6.3.4 Colour space encodings for the PCS
// A.3 PCS encodings
auto f = [](float x) {
if (x > powf(6.f / 29.f, 3))
return cbrtf(x);
return x / (3 * powf(6.f / 29.f, 2)) + 4.f / 29.f;
};
// "X/Xn is replaced by Xr/Xi (or Xa/Xmw)"
// 6.3.2.2 Translation between media-relative colorimetric data and ICC-absolute colorimetric data
// "The translation from ICC-absolute colorimetric data to media-relative colorimetry data is given by Equations
// Xr = (Xi/Xmw) * Xa
// where
// Xr media-relative colorimetric data (i.e. PCSXYZ);
// Xa ICC-absolute colorimetric data (i.e. nCIEXYZ);
// Xmw nCIEXYZ values of the media white point as specified in the mediaWhitePointTag;
// Xi PCSXYZ values of the PCS white point defined in 6.3.4.3."
// 6.3.4.3 PCS encodings for white and black
// "Table 14 — Encodings of PCS white point: X 0,9642 Y 1,0000 Z 0,8249"
// That's identical to the values in 7.2.16 PCS illuminant field (Bytes 68 to 79).
// 9.2.36 mediaWhitePointTag
// "For displays, the values specified shall be those of the PCS illuminant as defined in 7.2.16."
// ...so for displays, this is all equivalent I think? It's maybe different for OutputDevice profiles?
float Xn = white_point.X;
float Yn = white_point.Y;
float Zn = white_point.Z;
float x = xyz[0] / Xn;
float y = xyz[1] / Yn;
float z = xyz[2] / Zn;
float L = 116 * f(y) - 16;
float a = 500 * (f(x) - f(y));
float b = 200 * (f(y) - f(z));
return { L, a, b };
}
static TagSignature backward_transform_tag_for_rendering_intent(RenderingIntent rendering_intent) static TagSignature backward_transform_tag_for_rendering_intent(RenderingIntent rendering_intent)
{ {
// ICCv4, Table 25 — Profile type/profile tag and defined rendering intents // ICCv4, Table 25 — Profile type/profile tag and defined rendering intents
@ -1492,46 +1537,8 @@ ErrorOr<CIELAB> Profile::to_lab(ReadonlyBytes color) const
return Error::from_string_literal("ICC::Profile::to_lab: conversion for DeviceLink not implemented"); return Error::from_string_literal("ICC::Profile::to_lab: conversion for DeviceLink not implemented");
} }
// 6.3.2.2 Translation between media-relative colorimetric data and ICC-absolute colorimetric data FloatVector3 lab = lab_from_xyz(pcs, pcs_illuminant());
// 6.3.2.3 Computation of PCSLAB return CIELAB { lab[0], lab[1], lab[2] };
// 6.3.4 Colour space encodings for the PCS
// A.3 PCS encodings
auto f = [](float x) {
if (x > powf(6.f / 29.f, 3))
return cbrtf(x);
return x / (3 * powf(6.f / 29.f, 2)) + 4.f / 29.f;
};
// "X/Xn is replaced by Xr/Xi (or Xa/Xmw)"
// 6.3.2.2 Translation between media-relative colorimetric data and ICC-absolute colorimetric data
// "The translation from ICC-absolute colorimetric data to media-relative colorimetry data is given by Equations
// Xr = (Xi/Xmw) * Xa
// where
// Xr media-relative colorimetric data (i.e. PCSXYZ);
// Xa ICC-absolute colorimetric data (i.e. nCIEXYZ);
// Xmw nCIEXYZ values of the media white point as specified in the mediaWhitePointTag;
// Xi PCSXYZ values of the PCS white point defined in 6.3.4.3."
// 6.3.4.3 PCS encodings for white and black
// "Table 14 — Encodings of PCS white point: X 0,9642 Y 1,0000 Z 0,8249"
// That's identical to the values in 7.2.16 PCS illuminant field (Bytes 68 to 79).
// 9.2.36 mediaWhitePointTag
// "For displays, the values specified shall be those of the PCS illuminant as defined in 7.2.16."
// ...so for displays, this is all equivalent I think? It's maybe different for OutputDevice profiles?
float Xn = pcs_illuminant().X;
float Yn = pcs_illuminant().Y;
float Zn = pcs_illuminant().Z;
float x = pcs[0] / Xn;
float y = pcs[1] / Yn;
float z = pcs[2] / Zn;
float L = 116 * f(y) - 16;
float a = 500 * (f(x) - f(y));
float b = 200 * (f(y) - f(z));
return CIELAB { L, a, b };
} }
ErrorOr<void> Profile::convert_image(Gfx::Bitmap& bitmap, Profile const& source_profile) const ErrorOr<void> Profile::convert_image(Gfx::Bitmap& bitmap, Profile const& source_profile) const