[Image-SIG] I'm confused by alpha blending.
ned at nedbatchelder.com
Wed Mar 22 00:31:36 CET 2006
I found the problem, thanks to the code you posted. My destination
image was "RGBA", and I was viewing it in a web browser. Most of the
image had an opaque alpha channel, but where I had drawn the drop
shadows, it had the shadow's alpha values, so the white of the browser
was showing through. This isn't the most intuitive way for alpha
drawing to work. I guess I could see it both ways: if the destination
is opaque, it should stay opaque, or drawing pixels onto a destination
takes all the values from the source.
In any case, changing my destination image from RGBA to RGB solved the
Fredrik Lundh wrote:
>> are you 100% sure that the source pixels are black ?
> a quick way to find out is to do
> print shadow.convert("RGB").getcolors()
> Image-SIG maillist - Image-SIG at python.org
Ned Batchelder, http://nedbatchelder.com
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