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Unified Diff: src/codec/SkPngCodec.cpp

Issue 2180483003: Convert XYZ values from PNGs to D50 (Closed) Base URL: https://skia.googlesource.com/skia.git@master
Patch Set: Preemptively fix windows Created 4 years, 5 months ago
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Index: src/codec/SkPngCodec.cpp
diff --git a/src/codec/SkPngCodec.cpp b/src/codec/SkPngCodec.cpp
index 32308b263095676990884503a51376efb75ceabd..ee72af58ad46c517e3ec63da18746d4fe69257ef 100644
--- a/src/codec/SkPngCodec.cpp
+++ b/src/codec/SkPngCodec.cpp
@@ -13,6 +13,7 @@
#include "SkMath.h"
#include "SkOpts.h"
#include "SkPngCodec.h"
+#include "SkPoint3.h"
#include "SkSize.h"
#include "SkStream.h"
#include "SkSwizzler.h"
@@ -178,6 +179,62 @@ static constexpr float gSRGB_toXYZD50[] {
0.1430f, 0.0606f, 0.7139f, // * B
};
+static bool convert_to_D50(SkMatrix44* toXYZD50, float toXYZ[9], float whitePoint[2]) {
+ float wX = whitePoint[0];
+ float wY = whitePoint[1];
+ if (wX < 0.0f || wY < 0.0f || (wX + wY > 1.0f)) {
+ return false;
+ }
+
+ // Calculate the XYZ illuminant. Call this the src illuminant.
+ float wZ = 1.0f - wX - wY;
+ float scale = 1.0f / wY;
+ // TODO (msarett):
+ // What are common src illuminants? I'm guessing we will almost always see D65. Should
+ // we go ahead and save a precomputed D65->D50 Bradford matrix? Should we exit early if
+ // if the src illuminant is D50?
+ SkVector3 srcXYZ = SkVector3::Make(wX * scale, 1.0f, wZ * scale);
+
+ // The D50 illuminant.
+ SkVector3 dstXYZ = SkVector3::Make(0.96422f, 1.0f, 0.82521f);
+
+ // Calculate the chromatic adaptation matrix. We will use the Bradford method, thus
+ // the matrices below. The Bradford method is used by Adobe and is widely considered
+ // to be the best.
+ // http://www.brucelindbloom.com/index.html?Eqn_ChromAdapt.html
+ SkMatrix mA, mAInv;
+ mA.setAll(0.8951f, 0.2664f, -0.1614f, -0.7502f, 1.7135f, 0.0367f, 0.0389f, -0.0685f, 1.0296f);
+ mAInv.setAll(0.9869929f, -0.1470543f, 0.1599627f, 0.4323053f, 0.5183603f, 0.0492912f,
+ -0.0085287f, 0.0400428f, 0.9684867f);
+
+ // Map illuminant into cone response domain.
+ SkVector3 srcCone;
+ srcCone.fX = mA[0] * srcXYZ.fX + mA[1] * srcXYZ.fY + mA[2] * srcXYZ.fZ;
+ srcCone.fY = mA[3] * srcXYZ.fX + mA[4] * srcXYZ.fY + mA[5] * srcXYZ.fZ;
+ srcCone.fZ = mA[6] * srcXYZ.fX + mA[7] * srcXYZ.fY + mA[8] * srcXYZ.fZ;
+ SkVector3 dstCone;
+ dstCone.fX = mA[0] * dstXYZ.fX + mA[1] * dstXYZ.fY + mA[2] * dstXYZ.fZ;
+ dstCone.fY = mA[3] * dstXYZ.fX + mA[4] * dstXYZ.fY + mA[5] * dstXYZ.fZ;
+ dstCone.fZ = mA[6] * dstXYZ.fX + mA[7] * dstXYZ.fY + mA[8] * dstXYZ.fZ;
+
+ SkMatrix DXToD50;
+ DXToD50.setIdentity();
+ DXToD50[0] = dstCone.fX / srcCone.fX;
+ DXToD50[4] = dstCone.fY / srcCone.fY;
+ DXToD50[8] = dstCone.fZ / srcCone.fZ;
+ DXToD50.postConcat(mAInv);
+ DXToD50.preConcat(mA);
+
+ SkMatrix toXYZ3x3;
+ toXYZ3x3.setAll(toXYZ[0], toXYZ[3], toXYZ[6], toXYZ[1], toXYZ[4], toXYZ[7], toXYZ[2], toXYZ[5],
+ toXYZ[8]);
+ toXYZ3x3.postConcat(DXToD50);
+
+ toXYZD50->set3x3(toXYZ3x3[0], toXYZ3x3[1], toXYZ3x3[2], toXYZ3x3[3], toXYZ3x3[4], toXYZ3x3[5],
+ toXYZ3x3[6], toXYZ3x3[7], toXYZ3x3[8]);
+ return true;
+}
+
// Returns a colorSpace object that represents any color space information in
// the encoded data. If the encoded data contains no color space, this will
// return NULL.
@@ -213,24 +270,28 @@ sk_sp<SkColorSpace> read_color_space(png_structp png_ptr, png_infop info_ptr) {
}
// Next, check for chromaticities.
- png_fixed_point XYZ[9];
- float toXYZD50[9];
+ png_fixed_point toXYZFixed[9];
+ float toXYZ[9];
+ png_fixed_point whitePointFixed[2];
+ float whitePoint[2];
png_fixed_point gamma;
float gammas[3];
- if (png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &XYZ[0], &XYZ[1], &XYZ[2], &XYZ[3], &XYZ[4],
- &XYZ[5], &XYZ[6], &XYZ[7], &XYZ[8])) {
-
- // FIXME (msarett): Here we are treating XYZ values as D50 even though the color
- // temperature is unspecified. I suspect that this assumption
- // is most often ok, but we could also calculate the color
- // temperature (D value) and then convert the XYZ to D50. Maybe
- // we should add a new constructor to SkColorSpace that accepts
- // XYZ with D-Unkown?
+ if (png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &toXYZFixed[0], &toXYZFixed[1], &toXYZFixed[2],
+ &toXYZFixed[3], &toXYZFixed[4], &toXYZFixed[5], &toXYZFixed[6],
+ &toXYZFixed[7], &toXYZFixed[8]) &&
+ png_get_cHRM_fixed(png_ptr, info_ptr, &whitePointFixed[0], &whitePointFixed[1], nullptr,
+ nullptr, nullptr, nullptr, nullptr, nullptr))
+ {
for (int i = 0; i < 9; i++) {
- toXYZD50[i] = png_fixed_point_to_float(XYZ[i]);
+ toXYZ[i] = png_fixed_point_to_float(toXYZFixed[i]);
+ }
+ whitePoint[0] = png_fixed_point_to_float(whitePointFixed[0]);
+ whitePoint[1] = png_fixed_point_to_float(whitePointFixed[1]);
+
+ SkMatrix44 toXYZD50(SkMatrix44::kUninitialized_Constructor);
+ if (!convert_to_D50(&toXYZD50, toXYZ, whitePoint)) {
+ toXYZD50.set3x3RowMajorf(gSRGB_toXYZD50);
}
- SkMatrix44 mat(SkMatrix44::kUninitialized_Constructor);
- mat.set3x3RowMajorf(toXYZD50);
if (PNG_INFO_gAMA == png_get_gAMA_fixed(png_ptr, info_ptr, &gamma)) {
float value = png_inverted_fixed_point_to_float(gamma);
@@ -238,12 +299,12 @@ sk_sp<SkColorSpace> read_color_space(png_structp png_ptr, png_infop info_ptr) {
gammas[1] = value;
gammas[2] = value;
- return SkColorSpace_Base::NewRGB(gammas, mat);
+ return SkColorSpace_Base::NewRGB(gammas, toXYZD50);
}
// Default to sRGB gamma if the image has color space information,
// but does not specify gamma.
- return SkColorSpace::NewRGB(SkColorSpace::kSRGB_GammaNamed, mat);
+ return SkColorSpace::NewRGB(SkColorSpace::kSRGB_GammaNamed, toXYZD50);
}
// Last, check for gamma.
@@ -256,10 +317,10 @@ sk_sp<SkColorSpace> read_color_space(png_structp png_ptr, png_infop info_ptr) {
gammas[2] = value;
// Since there is no cHRM, we will guess sRGB gamut.
- SkMatrix44 mat(SkMatrix44::kUninitialized_Constructor);
- mat.set3x3RowMajorf(gSRGB_toXYZD50);
+ SkMatrix44 toXYZD50(SkMatrix44::kUninitialized_Constructor);
+ toXYZD50.set3x3RowMajorf(gSRGB_toXYZD50);
- return SkColorSpace_Base::NewRGB(gammas, mat);
+ return SkColorSpace_Base::NewRGB(gammas, toXYZD50);
}
#endif // LIBPNG >= 1.6
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