Merge remote-tracking branch 'origin/5.6' into 5.7v5.7.0-alpha1

Conflicts:
	.qmake.conf

Change-Id: Id59a8238134f1b0e172b22cd7e95d984a3f66401

1 files changed, 13 insertions, 2 deletions

diff --git a/src/plugins/imageformats/tiff/qtiffhandler.cpp b/src/plugins/imageformats/tiff/qtiffhandler.cpp
index e0c17ce..f72c2a0 100644
--- a/src/plugins/imageformats/tiff/qtiffhandler.cpp
+++ b/src/plugins/imageformats/tiff/qtiffhandler.cpp
@@ -257,8 +257,19 @@ bool QTiffHandlerPrivate::openForRead(QIODevice *device)
         format = QImage::Format_Indexed8;
     else if (samplesPerPixel < 4)
         format = QImage::Format_RGB32;
-    else
-        format = QImage::Format_ARGB32_Premultiplied;
+    else {
+        uint16 count;
+        uint16 *extrasamples;
+        // If there is any definition of the alpha-channel, libtiff will return premultiplied
+        // data to us. If there is none, libtiff will not touch it and  we assume it to be
+        // non-premultiplied, matching behavior of tested image editors, and how older Qt
+        // versions used to save it.
+        bool gotField = TIFFGetField(tiff, TIFFTAG_EXTRASAMPLES, &count, &extrasamples);
+        if (!gotField || !count || extrasamples[0] == EXTRASAMPLE_UNSPECIFIED)
+            format = QImage::Format_ARGB32;
+        else
+            format = QImage::Format_ARGB32_Premultiplied;
+    }
 
     headersRead = true;
     return true;