Am 29.08.2012 um 12:05 schrieb Samuel Rødal <[email protected]>:
> On 08/29/2012 11:54 AM, ext [email protected] wrote: >> Is the premultiplied specified when creating QImage or other ? > > The QImage constructor takes the QImage::Format. But if you load the > image from file it should already pick Format_ARGB32_Premultiplied by > default if the image has an alpha channel. As a matter of fact I am just in this very topic ("alpha-blending and premultiplied values") myself. I am not entirely sure, but I think when I loaded a PNG with alpha channel the format was *not* premultiplied alpha (but "normal" RGBA32 instead). It probably depends on the source file: if the original data is premultipied RGBA, then the resulting QImage is most likely also RGBA premultiplied. (Does the PNG file format support "premultiplied" RGBA?) In other words: "you get what you load"(tm) with QImage::load - which is good! Qt shouldn't convert data behind your back unnecessarily. So in my case the PNG contained "normal" RGBA values - so that was the pixel format of the resulting QImage. However: you can always query the pixel format after loading and explicitly request a (possibly costly) conversion, if necessary: http://qt-project.org/doc/qt-4.8/qimage.html#convertToFormat Cheers, Oliver _______________________________________________ Interest mailing list [email protected] http://lists.qt-project.org/mailman/listinfo/interest
