Wow! Thanks!
That is really fast!
Greetings,
Stephan
On 05/19/2011 01:04 AM, Matthew Flatt wrote:
I've added an argument to `get-argb-pixels' and `set-argb-pixels' to
make them work in premultiplied mode.
At Sat, 23 Apr 2011 22:54:47 +0200, Stephan Houben wrote:
Hi list,
Today I noticed that the bitmap's get-argb-pixels method returns
un-premultiplied alpha, even though it internally uses Cairo
which uses pre-multiplied alpha.
Looking at the code, it goes out of its way to convert
pre-multipled alpha to un-premultiplied alpha.
I then need to go out of my way again to convert it back to
premultiplied alpha. Which is inefficient and silly.
Could we have a method to get at the premultiplied alpha directly?
The Cairo folks chose it for a reason; if you want to interpolate between
two pixel values then only premultiplied alpha will give the correct result.
(See http://www.gimp.org/docs/plug-in/appendix-alpha.html for some discussion
on this).
I would therefore assume that it might be of wider interest than just me.
Thanks,
Stephan
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