Image : Prefer Qt's image reading to IECoreImage

This fixes GafferHQ#5695, by avoiding the colour conversions done by `IECoreImage::ImageReader` which were failing due to AcademySoftwareFoundation/OpenImageIO#4165. We want to phase `IECoreImage` out completely anyway, so this represents good progress in that direction.

Although `_qtPixmapFromImagePrimitive()` and the `Image( ImagePrimitive )` constructor are now completely unused in Gaffer itself, we can't remove them just yet because they are used in extension code at IE.

There's a reasonable case for using OpenImageIO here instead of Qt, to get access to a broader range of image formats and to match exactly the capabilities of ImageGadget. I tried implementing that but OpenImageIO isn't really usable from Python without `numpy`, and we don't ship with that module at present. It would be possible to implement an ImageBuf->QPixmap conversion in C++ and then bind that to Python if we consider this important. But practically speaking I think we only really care about common icon formats here, and Qt does fine with those, so I've gone with the simple option for now.

Changes.md

@@ -9,6 +9,9 @@ Fixes
   - Fixed hangs and crashes when using non-default session modes such as SVM shading.
   - Fixed failure to render background light in batch renders (#5234).
   - Fixed failure to update when reverting a background shader to previous values.
+- GafferUI :
+  - Fixed `Color space 'sRGB' could not be found` errors when running with certain custom OCIO configs (#5695).
+  - Fixed icon colours when running with an ACES OCIO config.
 
 Breaking Changes
 ----------------

python/GafferUI/Image.py

@@ -238,14 +238,7 @@ def __cacheGetter( cls, fileName ) :
 		if not resolvedFileName :
 			raise Exception( "Unable to find file \"%s\"" % fileName )
 
-		reader = IECore.Reader.create( resolvedFileName )
-
-		image = reader.read()
-		if not isinstance( image, IECoreImage.ImagePrimitive ) :
-			raise Exception( "File \"%s\" is not an image file" % resolvedFileName )
-
-		result = cls._qtPixmapFromImagePrimitive( image )
-
+		result = QtGui.QPixmap( resolvedFileName )
 		cost = result.width() * result.height() * ( 4 if result.hasAlpha() else 3 )
 
 		return ( result, cost )