Add SkDefaultXform as a catch-all to handle color conversions
I'd like to start optimizing the common case for color xforms,
but before doing that, I think it makes sense to have correct
code to support all xforms.
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2038823002
Review-Url: https://codereview.chromium.org/2038823002
diff --git a/src/core/SkColorSpace.cpp b/src/core/SkColorSpace.cpp
index 1652de3..6bc897c 100644
--- a/src/core/SkColorSpace.cpp
+++ b/src/core/SkColorSpace.cpp
@@ -719,19 +719,21 @@
return false;
}
+ // For this matrix to behave like our "to XYZ D50" matrices, it needs to be scaled.
+ constexpr float scale = 65535.0 / 32768.0;
float array[16];
- array[ 0] = SkFixedToFloat(read_big_endian_int(src));
- array[ 1] = SkFixedToFloat(read_big_endian_int(src + 4));
- array[ 2] = SkFixedToFloat(read_big_endian_int(src + 8));
- array[ 3] = SkFixedToFloat(read_big_endian_int(src + 36)); // translate R
- array[ 4] = SkFixedToFloat(read_big_endian_int(src + 12));
- array[ 5] = SkFixedToFloat(read_big_endian_int(src + 16));
- array[ 6] = SkFixedToFloat(read_big_endian_int(src + 20));
- array[ 7] = SkFixedToFloat(read_big_endian_int(src + 40)); // translate G
- array[ 8] = SkFixedToFloat(read_big_endian_int(src + 24));
- array[ 9] = SkFixedToFloat(read_big_endian_int(src + 28));
- array[10] = SkFixedToFloat(read_big_endian_int(src + 32));
- array[11] = SkFixedToFloat(read_big_endian_int(src + 44)); // translate B
+ array[ 0] = scale * SkFixedToFloat(read_big_endian_int(src));
+ array[ 1] = scale * SkFixedToFloat(read_big_endian_int(src + 4));
+ array[ 2] = scale * SkFixedToFloat(read_big_endian_int(src + 8));
+ array[ 3] = scale * SkFixedToFloat(read_big_endian_int(src + 36)); // translate R
+ array[ 4] = scale * SkFixedToFloat(read_big_endian_int(src + 12));
+ array[ 5] = scale * SkFixedToFloat(read_big_endian_int(src + 16));
+ array[ 6] = scale * SkFixedToFloat(read_big_endian_int(src + 20));
+ array[ 7] = scale * SkFixedToFloat(read_big_endian_int(src + 40)); // translate G
+ array[ 8] = scale * SkFixedToFloat(read_big_endian_int(src + 24));
+ array[ 9] = scale * SkFixedToFloat(read_big_endian_int(src + 28));
+ array[10] = scale * SkFixedToFloat(read_big_endian_int(src + 32));
+ array[11] = scale * SkFixedToFloat(read_big_endian_int(src + 44)); // translate B
array[12] = 0.0f;
array[13] = 0.0f;
array[14] = 0.0f;
diff --git a/src/core/SkColorSpaceXform.cpp b/src/core/SkColorSpaceXform.cpp
index 473e715..216e993 100644
--- a/src/core/SkColorSpaceXform.cpp
+++ b/src/core/SkColorSpaceXform.cpp
@@ -9,8 +9,8 @@
#include "SkColorSpace_Base.h"
#include "SkColorSpaceXform.h"
-bool compute_gamut_xform(SkMatrix44* srcToDst, const SkMatrix44& srcToXYZ,
- const SkMatrix44& dstToXYZ) {
+static inline bool compute_gamut_xform(SkMatrix44* srcToDst, const SkMatrix44& srcToXYZ,
+ const SkMatrix44& dstToXYZ) {
if (!dstToXYZ.invert(srcToDst)) {
return false;
}
@@ -22,15 +22,21 @@
std::unique_ptr<SkColorSpaceXform> SkColorSpaceXform::New(const sk_sp<SkColorSpace>& srcSpace,
const sk_sp<SkColorSpace>& dstSpace) {
if (!srcSpace || !dstSpace) {
+ // Invalid input
+ return nullptr;
+ }
+
+ if (as_CSB(srcSpace)->colorLUT() || as_CSB(dstSpace)->colorLUT()) {
+ // Unimplemented
+ return nullptr;
+ }
+
+ SkMatrix44 srcToDst(SkMatrix44::kUninitialized_Constructor);
+ if (!compute_gamut_xform(&srcToDst, srcSpace->xyz(), dstSpace->xyz())) {
return nullptr;
}
if (as_CSB(srcSpace)->gammas()->isValues() && as_CSB(dstSpace)->gammas()->isValues()) {
- SkMatrix44 srcToDst(SkMatrix44::kUninitialized_Constructor);
- if (!compute_gamut_xform(&srcToDst, srcSpace->xyz(), dstSpace->xyz())) {
- return nullptr;
- }
-
float srcGammas[3];
float dstGammas[3];
srcGammas[0] = as_CSB(srcSpace)->gammas()->fRed.fValue;
@@ -44,8 +50,25 @@
new SkGammaByValueXform(srcGammas, srcToDst, dstGammas));
}
- // Unimplemeted
- return nullptr;
+ return std::unique_ptr<SkColorSpaceXform>(
+ new SkDefaultXform(as_CSB(srcSpace)->gammas(), srcToDst, as_CSB(dstSpace)->gammas()));
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+static inline float byte_to_float(uint8_t v) {
+ return ((float) v) * (1.0f / 255.0f);
+}
+
+static inline uint8_t clamp_float_to_byte(float v) {
+ v = v * 255.0f;
+ if (v > 255.0f) {
+ return 255;
+ } else if (v <= 0.0f) {
+ return 0;
+ } else {
+ return (uint8_t) (v + 0.5f);
+ }
}
///////////////////////////////////////////////////////////////////////////////////////////////////
@@ -58,23 +81,12 @@
memcpy(fDstGammas, dstGammas, 3 * sizeof(float));
}
-static uint8_t clamp_float_to_byte(float v) {
- v = v * 255.0f;
- if (v > 255.0f) {
- return 255;
- } else if (v <= 0.0f) {
- return 0;
- } else {
- return (uint8_t) (v + 0.5f);
- }
-}
-
void SkGammaByValueXform::xform_RGBA_8888(uint32_t* dst, const uint32_t* src, uint32_t len) const {
while (len-- > 0) {
float srcFloats[3];
- srcFloats[0] = ((*src >> 0) & 0xFF) * (1.0f / 255.0f);
- srcFloats[1] = ((*src >> 8) & 0xFF) * (1.0f / 255.0f);
- srcFloats[2] = ((*src >> 16) & 0xFF) * (1.0f / 255.0f);
+ srcFloats[0] = byte_to_float((*src >> 0) & 0xFF);
+ srcFloats[1] = byte_to_float((*src >> 8) & 0xFF);
+ srcFloats[2] = byte_to_float((*src >> 16) & 0xFF);
// Convert to linear.
srcFloats[0] = pow(srcFloats[0], fSrcGammas[0]);
@@ -107,3 +119,153 @@
src++;
}
}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+// Interpolating lookup in a variably sized table.
+static inline float interp_lut(uint8_t byte, float* table, size_t tableSize) {
+ float index = byte_to_float(byte) * (tableSize - 1);
+ float diff = index - sk_float_floor2int(index);
+ return table[(int) sk_float_floor2int(index)] * (1.0f - diff) +
+ table[(int) sk_float_ceil2int(index)] * diff;
+}
+
+// Inverse table lookup. Ex: what index corresponds to the input value? This will
+// have strange results when the table is non-increasing. But any sane gamma
+// function will be increasing.
+// FIXME (msarett):
+// This is a placeholder implementation for inverting table gammas. First, I need to
+// verify if there are actually destination profiles that require this functionality.
+// Next, there are certainly faster and more robust approaches to solving this problem.
+// The LUT based approach in QCMS would be a good place to start.
+static inline float interp_lut_inv(float input, float* table, size_t tableSize) {
+ if (input <= table[0]) {
+ return table[0];
+ } else if (input >= table[tableSize - 1]) {
+ return 1.0f;
+ }
+
+ for (uint32_t i = 1; i < tableSize; i++) {
+ if (table[i] >= input) {
+ // We are guaranteed that input is greater than table[i - 1].
+ float diff = input - table[i - 1];
+ float distance = table[i] - table[i - 1];
+ float index = (i - 1) + diff / distance;
+ return index / (tableSize - 1);
+ }
+ }
+
+ // Should be unreachable, since we'll return before the loop if input is
+ // larger than the last entry.
+ SkASSERT(false);
+ return 0.0f;
+}
+
+SkDefaultXform::SkDefaultXform(const sk_sp<SkGammas>& srcGammas, const SkMatrix44& srcToDst,
+ const sk_sp<SkGammas>& dstGammas)
+ : fSrcGammas(srcGammas)
+ , fSrcToDst(srcToDst)
+ , fDstGammas(dstGammas)
+{}
+
+void SkDefaultXform::xform_RGBA_8888(uint32_t* dst, const uint32_t* src, uint32_t len) const {
+ while (len-- > 0) {
+ // Convert to linear.
+ // FIXME (msarett):
+ // Rather than support three different strategies of transforming gamma, QCMS
+ // builds a 256 entry float lookup table from the gamma info. This handles
+ // the gamma transform and the conversion from bytes to floats. This may
+ // be simpler and faster than our current approach.
+ float srcFloats[3];
+ for (int i = 0; i < 3; i++) {
+ const SkGammaCurve& gamma = (*fSrcGammas)[i];
+ uint8_t byte = (*src >> (8 * i)) & 0xFF;
+ if (gamma.isValue()) {
+ srcFloats[i] = pow(byte_to_float(byte), gamma.fValue);
+ } else if (gamma.isTable()) {
+ srcFloats[i] = interp_lut(byte, gamma.fTable.get(), gamma.fTableSize);
+ } else {
+ SkASSERT(gamma.isParametric());
+ float component = byte_to_float(byte);
+ if (component < gamma.fD) {
+ // Y = E * X + F
+ srcFloats[i] = gamma.fE * component + gamma.fF;
+ } else {
+ // Y = (A * X + B)^G + C
+ srcFloats[i] = pow(gamma.fA * component + gamma.fB, gamma.fG) + gamma.fC;
+ }
+ }
+ }
+
+ // Convert to dst gamut.
+ float dstFloats[3];
+ dstFloats[0] = srcFloats[0] * fSrcToDst.getFloat(0, 0) +
+ srcFloats[1] * fSrcToDst.getFloat(1, 0) +
+ srcFloats[2] * fSrcToDst.getFloat(2, 0) + fSrcToDst.getFloat(3, 0);
+ dstFloats[1] = srcFloats[0] * fSrcToDst.getFloat(0, 1) +
+ srcFloats[1] * fSrcToDst.getFloat(1, 1) +
+ srcFloats[2] * fSrcToDst.getFloat(2, 1) + fSrcToDst.getFloat(3, 1);
+ dstFloats[2] = srcFloats[0] * fSrcToDst.getFloat(0, 2) +
+ srcFloats[1] * fSrcToDst.getFloat(1, 2) +
+ srcFloats[2] * fSrcToDst.getFloat(2, 2) + fSrcToDst.getFloat(3, 2);
+
+ // Convert to dst gamma.
+ // FIXME (msarett):
+ // Rather than support three different strategies of transforming inverse gamma,
+ // QCMS builds a large float lookup table from the gamma info. Is this faster or
+ // better than our approach?
+ for (int i = 0; i < 3; i++) {
+ const SkGammaCurve& gamma = (*fDstGammas)[i];
+ if (gamma.isValue()) {
+ dstFloats[i] = pow(dstFloats[i], 1.0f / gamma.fValue);
+ } else if (gamma.isTable()) {
+ // FIXME (msarett):
+ // An inverse table lookup is particularly strange and non-optimal.
+ dstFloats[i] = interp_lut_inv(dstFloats[i], gamma.fTable.get(), gamma.fTableSize);
+ } else {
+ SkASSERT(gamma.isParametric());
+ // FIXME (msarett):
+ // This is a placeholder implementation for inverting parametric gammas.
+ // First, I need to verify if there are actually destination profiles that
+ // require this functionality. Next, I need to explore other possibilities
+ // for this implementation. The LUT based approach in QCMS would be a good
+ // place to start.
+
+ // We need to take the inverse of a piecewise function. Assume that
+ // the gamma function is continuous, or this won't make much sense
+ // anyway.
+ // Plug in |fD| to the first equation to calculate the new piecewise
+ // interval. Then simply use the inverse of the original functions.
+ float interval = gamma.fE * gamma.fD + gamma.fF;
+ if (dstFloats[i] < interval) {
+ // X = (Y - F) / E
+ if (0.0f == gamma.fE) {
+ // The gamma curve for this segment is constant, so the inverse
+ // is undefined.
+ dstFloats[i] = 0.0f;
+ } else {
+ dstFloats[i] = (dstFloats[i] - gamma.fF) / gamma.fE;
+ }
+ } else {
+ // X = ((Y - C)^(1 / G) - B) / A
+ if (0.0f == gamma.fA || 0.0f == gamma.fG) {
+ // The gamma curve for this segment is constant, so the inverse
+ // is undefined.
+ dstFloats[i] = 0.0f;
+ } else {
+ dstFloats[i] = (pow(dstFloats[i] - gamma.fC, 1.0f / gamma.fG) - gamma.fB)
+ / gamma.fA;
+ }
+ }
+ }
+ }
+
+ *dst = SkPackARGB32NoCheck(((*src >> 24) & 0xFF),
+ clamp_float_to_byte(dstFloats[0]),
+ clamp_float_to_byte(dstFloats[1]),
+ clamp_float_to_byte(dstFloats[2]));
+
+ dst++;
+ src++;
+ }
+}
diff --git a/src/core/SkColorSpaceXform.h b/src/core/SkColorSpaceXform.h
index c3010f0..d54d1b8 100644
--- a/src/core/SkColorSpaceXform.h
+++ b/src/core/SkColorSpaceXform.h
@@ -9,8 +9,9 @@
#define SkColorSpaceXform_DEFINED
#include "SkColorSpace.h"
+#include "SkColorSpace_Base.h"
-class SkColorSpaceXform {
+class SkColorSpaceXform : SkNoncopyable {
public:
/**
@@ -48,4 +49,24 @@
friend class SkColorSpaceXform;
};
+/**
+ * Works for any valid src and dst profiles.
+ */
+class SkDefaultXform : public SkColorSpaceXform {
+public:
+
+ void xform_RGBA_8888(uint32_t* dst, const uint32_t* src, uint32_t len) const override;
+
+private:
+ SkDefaultXform(const sk_sp<SkGammas>& srcGammas, const SkMatrix44& srcToDst,
+ const sk_sp<SkGammas>& dstGammas);
+
+ sk_sp<SkGammas> fSrcGammas;
+ const SkMatrix44 fSrcToDst;
+ sk_sp<SkGammas> fDstGammas;
+
+ friend class SkColorSpaceXform;
+ friend class ColorSpaceXformTest;
+};
+
#endif
diff --git a/src/core/SkColorSpace_Base.h b/src/core/SkColorSpace_Base.h
index 68514d0..ffab17a 100644
--- a/src/core/SkColorSpace_Base.h
+++ b/src/core/SkColorSpace_Base.h
@@ -78,6 +78,11 @@
return fRed.isValue() && fGreen.isValue() && fBlue.isValue();
}
+ const SkGammaCurve& operator[](int i) {
+ SkASSERT(0 <= i && i < 3);
+ return (&fRed)[i];
+ }
+
const SkGammaCurve fRed;
const SkGammaCurve fGreen;
const SkGammaCurve fBlue;
@@ -117,6 +122,8 @@
const sk_sp<SkGammas>& gammas() const { return fGammas; }
+ SkColorLookUpTable* colorLUT() const { return fColorLUT.get(); }
+
/**
* Writes this object as an ICC profile.
*/
diff --git a/tests/ColorSpaceXformTest.cpp b/tests/ColorSpaceXformTest.cpp
new file mode 100644
index 0000000..220509b
--- /dev/null
+++ b/tests/ColorSpaceXformTest.cpp
@@ -0,0 +1,103 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "Resources.h"
+#include "SkCodec.h"
+#include "SkColorPriv.h"
+#include "SkColorSpace.h"
+#include "SkColorSpace_Base.h"
+#include "SkColorSpaceXform.h"
+#include "Test.h"
+
+class ColorSpaceXformTest {
+public:
+ static SkDefaultXform* CreateDefaultXform(const sk_sp<SkGammas>& srcGamma,
+ const SkMatrix44& srcToDst, const sk_sp<SkGammas>& dstGamma) {
+ return new SkDefaultXform(srcGamma, srcToDst, dstGamma);
+ }
+};
+
+static void test_xform(skiatest::Reporter* r, const sk_sp<SkGammas>& gammas) {
+ // Arbitrary set of 10 pixels
+ constexpr int width = 10;
+ constexpr uint32_t srcPixels[width] = {
+ 0xFFABCDEF, 0xFF146829, 0xFF382759, 0xFF184968, 0xFFDE8271,
+ 0xFF32AB52, 0xFF0383BC, 0xFF000000, 0xFFFFFFFF, 0xFFDDEEFF, };
+ uint32_t dstPixels[width];
+
+ // Identity matrix
+ SkMatrix44 srcToDst = SkMatrix44::I();
+
+ // Create and perform xform
+ std::unique_ptr<SkColorSpaceXform> xform(
+ ColorSpaceXformTest::CreateDefaultXform(gammas, srcToDst, gammas));
+ xform->xform_RGBA_8888(dstPixels, srcPixels, width);
+
+ // Since the matrix is the identity, and the gamma curves match, the pixels
+ // should be unchanged.
+ for (int i = 0; i < width; i++) {
+ // TODO (msarett):
+ // As the implementation changes, we may want to use a tolerance here.
+ REPORTER_ASSERT(r, ((srcPixels[i] >> 0) & 0xFF) == SkGetPackedR32(dstPixels[i]));
+ REPORTER_ASSERT(r, ((srcPixels[i] >> 8) & 0xFF) == SkGetPackedG32(dstPixels[i]));
+ REPORTER_ASSERT(r, ((srcPixels[i] >> 16) & 0xFF) == SkGetPackedB32(dstPixels[i]));
+ REPORTER_ASSERT(r, ((srcPixels[i] >> 24) & 0xFF) == SkGetPackedA32(dstPixels[i]));
+ }
+}
+
+DEF_TEST(ColorSpaceXform_TableGamma, r) {
+ // Lookup-table based gamma curves
+ SkGammaCurve red, green, blue;
+ constexpr size_t tableSize = 10;
+ red.fTable = std::unique_ptr<float[]>(new float[tableSize]);
+ green.fTable = std::unique_ptr<float[]>(new float[tableSize]);
+ blue.fTable = std::unique_ptr<float[]>(new float[tableSize]);
+ red.fTableSize = green.fTableSize = blue.fTableSize = 10;
+ red.fTable[0] = green.fTable[0] = blue.fTable[0] = 0.00f;
+ red.fTable[1] = green.fTable[1] = blue.fTable[1] = 0.05f;
+ red.fTable[2] = green.fTable[2] = blue.fTable[2] = 0.10f;
+ red.fTable[3] = green.fTable[3] = blue.fTable[3] = 0.15f;
+ red.fTable[4] = green.fTable[4] = blue.fTable[4] = 0.25f;
+ red.fTable[5] = green.fTable[5] = blue.fTable[5] = 0.35f;
+ red.fTable[6] = green.fTable[6] = blue.fTable[6] = 0.45f;
+ red.fTable[7] = green.fTable[7] = blue.fTable[7] = 0.60f;
+ red.fTable[8] = green.fTable[8] = blue.fTable[8] = 0.75f;
+ red.fTable[9] = green.fTable[9] = blue.fTable[9] = 1.00f;
+ sk_sp<SkGammas> gammas =
+ sk_make_sp<SkGammas>(std::move(red), std::move(green), std::move(blue));
+ test_xform(r, gammas);
+}
+
+DEF_TEST(ColorSpaceXform_ParametricGamma, r) {
+ // Parametric gamma curves
+ SkGammaCurve red, green, blue;
+
+ // Interval, switch xforms at 0.5f
+ red.fD = green.fD = blue.fD = 0.5f;
+
+ // First equation, Y = 0.5f * X
+ red.fE = green.fE = blue.fE = 0.5f;
+
+ // Second equation, Y = ((1.0f * X) + 0.0f) ^ 3.0f + 0.125f
+ // Note that the function is continuous:
+ // 0.5f * 0.5f = ((1.0f * 0.5f) + 0.0f) ^ 3.0f + 0.125f = 0.25f
+ red.fA = green.fA = blue.fA = 1.0f;
+ red.fB = green.fB = blue.fB = 0.0f;
+ red.fC = green.fC = blue.fC = 0.125f;
+ red.fG = green.fG = blue.fG = 3.0f;
+ sk_sp<SkGammas> gammas = sk_make_sp<SkGammas>(std::move(red), std::move(green), std::move(blue));
+ test_xform(r, gammas);
+}
+
+DEF_TEST(ColorSpaceXform_ExponentialGamma, r) {
+ // Exponential gamma curves
+ SkGammaCurve red, green, blue;
+ red.fValue = green.fValue = blue.fValue = 4.0f;
+ sk_sp<SkGammas> gammas =
+ sk_make_sp<SkGammas>(std::move(red), std::move(green), std::move(blue));
+ test_xform(r, gammas);
+}