Set SkColorSpace object for PNGs and parse ICC profiles

src/codec/SkPngCodec.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
 #include "SkColorTable.h"
@@ skipping 147 matching lines @@
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 // Creation
 ///////////////////////////////////////////////////////////////////////////////
 
 bool SkPngCodec::IsPng(const char* buf, size_t bytesRead) {
     return !png_sig_cmp((png_bytep) buf, (png_size_t)0, bytesRead);
 }
 
+// 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.
+SkColorSpace* read_color_space(png_structp png_ptr, png_infop info_ptr) {
+
+    // First check for an ICC profile
+    png_bytep profile;
+    png_uint_32 length;
+    // The below variables are unused, however, we need to pass them in anyway or
+    // png_get_iCCP() will return nothing.
+    // Could knowing the |name| of the profile ever be interesting?  Maybe for debugging?
+    png_charp name;
+    // The |compression| is uninteresting since:
+    //   (1) libpng has already decompressed the profile for us.
+    //   (2) "deflate" is the only mode of decompression that libpng supports.
+    int compression;
+    if (PNG_INFO_iCCP == png_get_iCCP(png_ptr, info_ptr, &name, &compression, &profile,
+            &length)) {
+        return SkColorSpace::NewICC(profile, length);
+    }
+
+    // Second, check for sRGB.
+    if (png_get_valid(png_ptr, info_ptr, PNG_INFO_sRGB)) {
+
+        // sRGB chunks also store a rendering intent: Absolute, Relative,
+        // Perceptual, and Saturation.
+        // FIXME (msarett): Extract this information from the sRGB chunk once
+        //                  we are able to handle this information in
+        //                  SkColorSpace.
+        return SkColorSpace::NewNamed(SkColorSpace::kSRGB_Named);
+    }
+
+    // Next, check for chromaticities.
+    png_fixed_point XYZ[9];
+    SkFloat3x3 toXYZD50;
+    png_fixed_point gamma;
+    SkFloat3 gammas;
+    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?
+        for (int i = 0; i < 9; i++) {
+
+            // This is identical libpng's fixed point -> double conversion (except that

[scroggo, 2016/02/29 22:18:49]

nit: identical to* ?

[msarett, 2016/03/01 00:39:35]

Done.

+            // we are converting to floats).  We choose to do the conversion ourselves
+            // rather than convert fixed point -> double -> float.
+            toXYZD50.fMat[i] = ((float) XYZ[i]) * 0.00001f;
+        }
+
+        if (!(PNG_INFO_gAMA == png_get_gAMA_fixed(png_ptr, info_ptr, &gamma))) {
+
+            // If the image does not specify gamma, let's choose linear.  Should we default
+            // to sRGB?  Most images are intended to be sRGB (gamma = 2.2f).
+            gamma = PNG_GAMMA_LINEAR;
+        }
+        gammas.fVec[0] = gammas.fVec[1] = gammas.fVec[2] = ((float) gamma) * 0.00001f;
+
+        return SkColorSpace::NewRGB(toXYZD50, gammas);
+    }
+
+    // Last, check for gamma.
+    if (PNG_INFO_gAMA == png_get_gAMA_fixed(png_ptr, info_ptr, &gamma)) {
+
+        // Guess a default value for cHRM?  Or should we just give up?
+        // Here we use the identity matrix as a default.
+        // FIXME (msarett): Should SkFloat3x3 have a method to set the identity matrix?
+        memset(toXYZD50.fMat, 0, 9 * sizeof(float));
+        toXYZD50.fMat[0] = toXYZD50.fMat[4] = toXYZD50.fMat[8] = 1.0f;
+
+        // Set the gammas.
+        gammas.fVec[0] = gammas.fVec[1] = gammas.fVec[2] = ((float) gamma) * 0.00001f;

[scroggo, 2016/02/29 22:18:49]

Should this be a function? (Perhaps a static function in this file, unless we
decide it's needed elsewhere?)

[msarett, 2016/03/01 00:39:34]

Yes that's a little clearer.

[scroggo, 2016/03/01 14:42:29]

Much clearer, thanks!

+
+        return SkColorSpace::NewRGB(toXYZD50, gammas);
+    }
+
+    // Finally, what should we do if there is no color space information in the PNG?
+    // The specification says that this indicates "gamma is unknown" and that the
+    // "color is device dependent".  I'm assuming we can represent this with NULL.
+    // But should we guess sRGB?  Most images are sRGB, even if they don't specify.
+    return nullptr;
+}
+
 // Reads the header and initializes the output fields, if not NULL.
 //
 // @param stream Input data. Will be read to get enough information to properly
 //      setup the codec.
 // @param chunkReader SkPngChunkReader, for reading unknown chunks. May be NULL.
 //      If not NULL, png_ptr will hold an *unowned* pointer to it. The caller is
 //      expected to continue to own it for the lifetime of the png_ptr.
 // @param png_ptrp Optional output variable. If non-NULL, will be set to a new
 //      png_structp on success.
 // @param info_ptrp Optional output variable. If non-NULL, will be set to a new
@@ skipping 145 matching lines @@
         *png_ptrp = png_ptr;
     }
     if (info_ptrp) {
         *info_ptrp = info_ptr;
     }
 
     return true;
 }
 
 SkPngCodec::SkPngCodec(const SkImageInfo& info, SkStream* stream, SkPngChunkReader* chunkReader,
-                       png_structp png_ptr, png_infop info_ptr, int bitDepth, int numberPasses)
-    : INHERITED(info, stream)
+                       png_structp png_ptr, png_infop info_ptr, int bitDepth, int numberPasses,
+                       SkColorSpace* colorSpace)
+    : INHERITED(info, stream, colorSpace)
     , fPngChunkReader(SkSafeRef(chunkReader))
     , fPng_ptr(png_ptr)
     , fInfo_ptr(info_ptr)
     , fSrcConfig(SkSwizzler::kUnknown)
     , fNumberPasses(numberPasses)
     , fBitDepth(bitDepth)
 {}
 
 SkPngCodec::~SkPngCodec() {
     this->destroyReadStruct();
@@ skipping 189 matching lines @@
     if (colorPtr) {
         return get_color_table_fill_value(colorType, colorPtr, 0);
     }
     return INHERITED::onGetFillValue(colorType);
 }
 
 // Subclass of SkPngCodec which supports scanline decoding
 class SkPngScanlineDecoder : public SkPngCodec {
 public:
     SkPngScanlineDecoder(const SkImageInfo& srcInfo, SkStream* stream,
-            SkPngChunkReader* chunkReader, png_structp png_ptr, png_infop info_ptr, int bitDepth)
-        : INHERITED(srcInfo, stream, chunkReader, png_ptr, info_ptr, bitDepth, 1)
+            SkPngChunkReader* chunkReader, png_structp png_ptr, png_infop info_ptr, int bitDepth,
+            SkColorSpace* colorSpace)
+        : INHERITED(srcInfo, stream, chunkReader, png_ptr, info_ptr, bitDepth, 1, colorSpace)
         , fSrcRow(nullptr)
     {}
 
     Result onStartScanlineDecode(const SkImageInfo& dstInfo, const Options& options,
             SkPMColor ctable[], int* ctableCount) override {
         if (!conversion_possible(dstInfo, this->getInfo())) {
             return kInvalidConversion;
         }
 
         const Result result = this->initializeSwizzler(dstInfo, options, ctable,
@@ skipping 44 matching lines @@
     uint8_t*                    fSrcRow;
 
     typedef SkPngCodec INHERITED;
 };
 
 
 class SkPngInterlacedScanlineDecoder : public SkPngCodec {
 public:
     SkPngInterlacedScanlineDecoder(const SkImageInfo& srcInfo, SkStream* stream,
             SkPngChunkReader* chunkReader, png_structp png_ptr, png_infop info_ptr,
-            int bitDepth, int numberPasses)
-        : INHERITED(srcInfo, stream, chunkReader, png_ptr, info_ptr, bitDepth, numberPasses)
+            int bitDepth, int numberPasses, SkColorSpace* colorSpace)
+        : INHERITED(srcInfo, stream, chunkReader, png_ptr, info_ptr, bitDepth, numberPasses,
+                    colorSpace)
         , fHeight(-1)
         , fCanSkipRewind(false)
     {
         SkASSERT(numberPasses != 1);
     }
 
     Result onStartScanlineDecode(const SkImageInfo& dstInfo, const Options& options,
             SkPMColor ctable[], int* ctableCount) override {
         if (!conversion_possible(dstInfo, this->getInfo())) {
             return kInvalidConversion;
@@ skipping 110 matching lines @@
     png_infop info_ptr;
     SkImageInfo imageInfo;
     int bitDepth;
     int numberPasses;
 
     if (!read_header(stream, chunkReader, &png_ptr, &info_ptr, &imageInfo, &bitDepth,
                      &numberPasses)) {
         return nullptr;
     }
 
+    SkColorSpace* colorSpace = read_color_space(png_ptr, info_ptr);
+
     if (1 == numberPasses) {
         return new SkPngScanlineDecoder(imageInfo, streamDeleter.detach(), chunkReader,
-                                        png_ptr, info_ptr, bitDepth);
+                                        png_ptr, info_ptr, bitDepth, colorSpace);
     }
 
     return new SkPngInterlacedScanlineDecoder(imageInfo, streamDeleter.detach(), chunkReader,
-                                              png_ptr, info_ptr, bitDepth, numberPasses);
+                                              png_ptr, info_ptr, bitDepth, numberPasses,
+                                              colorSpace);
 }