Color-correct PNG images that have an sRGB chunk

Source/platform/image-decoders/png/PNGImageDecoder.cpp

 /*
  * Copyright (C) 2006 Apple Computer, Inc.
  * Copyright (C) Research In Motion Limited 2009-2010. All rights reserved.
  *
  * Portions are Copyright (C) 2001 mozilla.org
  *
  * Other contributors:
  *   Stuart Parmenter <stuart@mozilla.com>
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 171 matching lines @@
     void createRowBuffer(int size) { m_rowBuffer = adoptArrayPtr(new png_byte[size]); }
     qcms_transform* colorTransform() const { return m_transform; }
 
     void clearColorTransform()
     {
         if (m_transform)
             qcms_transform_release(m_transform);
         m_transform = 0;
     }
 
-    void createColorTransform(const ColorProfile& colorProfile, bool hasAlpha)
+    void createColorTransform(const ColorProfile& colorProfile, bool hasAlpha, bool sRGB)
     {
         clearColorTransform();
 
-        if (colorProfile.isEmpty())
+        if (colorProfile.isEmpty() && !sRGB)
             return;
         qcms_profile* deviceProfile = ImageDecoder::qcmsOutputDeviceProfile();
         if (!deviceProfile)
             return;
-        qcms_profile* inputProfile = qcms_profile_from_memory(colorProfile.data(), colorProfile.size());
+        qcms_profile* inputProfile = 0;
+        if (!colorProfile.isEmpty())

[Ken Russell (switch to Gerrit), 2014/12/03 23:50:02]

I think this should read "if (sRGB) { ... } else {
ASSERT(!colorProfile.isEmpty()); ... }" so that sRGB is preferred over other
color profiles that might be embedded in the file, per the PNG spec.

[Noel Gordon, 2014/12/05 04:12:43]

I think the spec says that a PNG should have an sRGB or an iCCP, but not both. 
Doesn't say how to tie-break, so interesting point.

The preference selection is done in readColorProfile, so if I reading that you'd
prefer sRGB, I can add it there.

Note: mozilla prefers iCCP over sRGB [1].  I don't think it matters though. 
Thoughts?

http://lxr.mozilla.org/mozilla-central/source/image/decoders/nsPNGDecoder.cpp...

[Ken Russell (switch to Gerrit), 2014/12/05 19:24:53]

I see. Thanks for clarifying that. This looks fine then.

+            inputProfile = qcms_profile_from_memory(colorProfile.data(), colorProfile.size());
+        else if (sRGB)
+            inputProfile = qcms_profile_sRGB();
         if (!inputProfile)
             return;
         // We currently only support color profiles for RGB and RGBA images.
         ASSERT(icSigRgbData == qcms_profile_get_color_space(inputProfile));
         qcms_data_type dataFormat = hasAlpha ? QCMS_DATA_RGBA_8 : QCMS_DATA_RGB_8;
         // FIXME: Don't force perceptual intent if the image profile contains an intent.
         m_transform = qcms_transform_create(inputProfile, dataFormat, deviceProfile, dataFormat, QCMS_INTENT_PERCEPTUAL);
         qcms_profile_release(inputProfile);
     }
 #endif
@@ skipping 57 matching lines @@
 
 bool PNGImageDecoder::setFailed()
 {
     if (m_doNothingOnFailure)
         return false;
     m_reader.clear();
     return ImageDecoder::setFailed();
 }
 
 #if USE(QCMSLIB)
-static void readColorProfile(png_structp png, png_infop info, ColorProfile& colorProfile)
+static void readColorProfile(png_structp png, png_infop info, ColorProfile& colorProfile, bool& sRGB)

[Sami, 2014/12/04 12:51:23]

Generally output parameters should be pointers rather than references.

[Noel Gordon, 2014/12/05 04:12:43]

Blink style is that output parameters are references, no?

[Sami, 2014/12/05 11:50:43]

Ah, sorry, I've spent too much time in Chromium land recently :)

 {
 #ifdef PNG_iCCP_SUPPORTED
     char* profileName;
     int compressionType;
 #if (PNG_LIBPNG_VER < 10500)
     png_charp profile;
 #else
     png_bytep profile;
 #endif
     png_uint_32 profileLength;
-    if (!png_get_iCCP(png, info, &profileName, &compressionType, &profile, &profileLength))
+    if (!png_get_iCCP(png, info, &profileName, &compressionType, &profile, &profileLength)) {
+        ASSERT(!png_get_valid(png, info, PNG_INFO_iCCP));
+        // No color profile: check the sRGB chunk.
+        // FIXME: but only if no cHRM or gAMA chunk was seen?
+        // if (info->chroma_or_gamma & (PNG_INFO_cHRM | PNG_INFO_gAMA))
+        //    return;
+        sRGB = png_get_valid(png, info, PNG_INFO_sRGB);

[Sami, 2014/12/04 12:51:23]

Could we instead encode this information in |colorProfile| instead of adding a
redundant-seeming flag?

[Noel Gordon, 2014/12/05 04:12:43]

Not easily Sami. ColorProfile is not a class, it's a typedef to WTF::Vector.

[Sami, 2014/12/05 11:50:43]

Right, I was thinking it was a string identifier but looks like it's just a blob
of data. Nevermind then.

         return;
+    }
 
     // Only accept RGB color profiles from input class devices.
     bool ignoreProfile = false;
     char* profileData = reinterpret_cast<char*>(profile);
     if (profileLength < ImageDecoder::iccColorProfileHeaderLength)
         ignoreProfile = true;
     else if (!ImageDecoder::rgbColorProfile(profileData, profileLength))
         ignoreProfile = true;
     else if (!ImageDecoder::inputDeviceColorProfile(profileData, profileLength))
         ignoreProfile = true;
@@ skipping 54 matching lines @@
         png_set_gray_to_rgb(png);
 
 #if USE(QCMSLIB)
     if ((colorType & PNG_COLOR_MASK_COLOR) && !m_ignoreGammaAndColorProfile) {
         // We only support color profiles for color PALETTE and RGB[A] PNG. Supporting
         // color profiles for gray-scale images is slightly tricky, at least using the
         // CoreGraphics ICC library, because we expand gray-scale images to RGB but we
         // do not similarly transform the color profile. We'd either need to transform
         // the color profile or we'd need to decode into a gray-scale image buffer and
         // hand that to CoreGraphics.
+        bool sRGB = false;
         ColorProfile colorProfile;
-        readColorProfile(png, info, colorProfile);
+        readColorProfile(png, info, colorProfile, sRGB);
         bool decodedImageHasAlpha = (colorType & PNG_COLOR_MASK_ALPHA) || trnsCount;
-        m_reader->createColorTransform(colorProfile, decodedImageHasAlpha);
+        m_reader->createColorTransform(colorProfile, decodedImageHasAlpha, sRGB);
         m_hasColorProfile = !!m_reader->colorTransform();
     }
 #endif
 
     if (!m_hasColorProfile) {
         // Deal with gamma and keep it under our control.
         double gamma;
         if (!m_ignoreGammaAndColorProfile && png_get_gAMA(png, info, &gamma)) {
             if ((gamma <= 0.0) || (gamma > cMaxGamma)) {
                 gamma = cInverseGamma;
@@ skipping 172 matching lines @@
     // has failed.
     if (!m_reader->decode(*m_data, onlySize) && isAllDataReceived())
         setFailed();
     // If we're done decoding the image, we don't need the PNGImageReader
     // anymore.  (If we failed, |m_reader| has already been cleared.)
     else if (isComplete())
         m_reader.clear();
 }
 
 } // namespace blink