Wrong anti-aliasing on fully transparent edges

[GoogleCodeExporter]

What steps will reproduce the problem?

Scale an image that has color and full transparency adjacent on a diagonal 
edges.

Expected output is a gradient from the color to transparent.
Currently, there's a gradient towards the color value of the transparent pixel 
at the same time, wich creates noticeable artifacts when the alpha channel is 
removed later.

Attachment info: 'In' is scaled 800%. 'Out' is HQ4X scaled 400%.

Original issue reported on code.google.com by cabur...@gmail.com on 16 Sep 2012 at 12:08

Attachments:

• in.png

[GoogleCodeExporter]

I think the problem is that this does not support alpha channels at all.  To do 
so properly we would need the api to have the ability specify a full "alpha 
label" which includes:

straight / premul / none (none being what is supported now)
if premul: the RGB background color to premul with
optional "inverse" bit (is the alpha "inverted")

Original comment by anbaricf...@gmail.com on 25 Jan 2014 at 8:54