Bug 61829

Confirmed for CVS HEAD. 

This appears to be a Qt bug. I've sent a bug report (with a suggested fix) to qt-bugs. Will wait for a response before closing.

Created attachment 7269 [details]
Patch, as proposed to TT

CVS commit by bhards: 

This patch fixes a bug report that was logged against KDE for not
handling gamma correctly (http://bugs.kde.org/show_bug.cgi?id=61829).

Using the example/showimg/showimg example in qt-3.3, the two test
case images (linked in the original bug report) look the same.
That isn't the case with a non-Qt based application, such as Mozilla.

The gamma-yes.png file should look a lot lighter in the blue section.

The problem is in src/kernel/qpngio.cpp::setup_qt()
    if ( screen_gamma != 0.0 && png_get_valid(png_ptr, info_ptr,PNG_INFO_gAMA) ) {
        double file_gamma;
        png_get_gAMA(png_ptr, info_ptr, &file_gamma);
        png_set_gamma( png_ptr, screen_gamma, file_gamma );
    }
which is wrong, because file gamma needs to be handled whether or not
there is a non-default screen gamma value.

qt-bugs@TT issue : N55198

CCMAIL: 61829-done@bugs.kde.org


  A            0053-png-gamma-fix.diff   1.1
  M +1 -1      README   1.28


--- qt-copy/patches/README  #1.27:1.28
@@ -1,4 +1,4 @@
 Please assign the numbers incrementally, and don't reuse them. The next one:
-#0053
+#0054
 
 This directory contains patches for Qt that haven't been accepted by TrollTech

SVN commit 476941 by charles:


Fix gamma correction semi-properly.  The patch that does it incorrectly
in qt-copy should go away now.

This has seen minimal review on kfm-devel...

CCMAIL:61829@bugs.kde.org



 M  +11 -2     loader.cpp  


--- branches/KDE/3.5/kdelibs/khtml/misc/loader.cpp #476940:476941
@@ -821,7 +821,16 @@
 #ifdef CACHE_DEBUG
             kdDebug(6060) << "CachedImage::data(): reloading as pixmap:" << endl;
 #endif
-            p = new QPixmap( _buffer.buffer() );
+            p = new QPixmap;
+            {
+            	QBuffer buffer(_buffer.buffer());
+            	buffer.open(IO_ReadOnly);
+                QImageIO io( &buffer, 0 );
+                io.setGamma(2.2); // hardcoded "reasonable value"
+                bool result = io.read();
+                if (result) p->convertFromImage(io.image(), 0);
+            }
+
             // set size of image.
 #ifdef CACHE_DEBUG
             kdDebug(6060) << "CachedImage::data(): image is null: " << p->isNull() << endl;
@@ -836,7 +845,7 @@
 
             for (QPtrDictIterator<CachedObjectClient> it( m_clients ); it.current();)
                 it()->notifyFinished( this );
-	    m_status = Cached; //all done
+            m_status = Cached; //all done
         }
     }
 }

I can see how that might work around the problem for khtml, but what about the direct users of kimgio? 

Also, can you tell me what you think is wrong with the qt-copy patch?

Brad