[Qt-interest] QImage and ARGB32_Premultiplied

[Joshua Grauman]

Hello all,

I've been trying to figure out how to combine two QImages in the best way 
possible (to fade between them) and have some easy questions that have 
been troubling me and so I thought I'd ask for some clarification.

1) If I have one QImage that is ARGB32_Premultiplied and one that is 
ARGB32, if I assign one into the other (ie. image1=image2), will QImage do 
the conversion for me?

2) When calling QImage::setPixel() and QImage::pixel() on a 
ARGB32_Premultiplied QImage, do these functions set/return premultiplied 
values, or does QImage convert the values. Ie. if I call 
setPixel(x,y,0x80FF00FF) will the pixel have an Alpha:128, Red:255, 
Blue:0, Green:255? or are the Red, Green, and Blue values invalid in this 
case?

3) Seeing that setAlphaChannel() is deprecated, what is the fastest way to 
set the alpha channel to a single value for an entire image (for an 
ARGB32_Premultiplied QImage). Do I have to iterate over each pixel and 
calculate/set the premultiplied values?

Thanks, that's it for now!

Josh