[artworks] Alpha mask option for bitmap export
- From: Martin Wuerthner <lists@xxxxxxxxxxxxxxx>
- To: artworks@xxxxxxxxxxxxx
- Date: Fri, 27 Feb 2009 19:29:24 +0100
I have just managed to add alpha mask support to Sprite and PNG
export, so using the forthcoming ArtWorks 2.9 you will finally be able
to export bitmaps with alpha transparency information.
Alpha masks offer 256 levels of transparency ranging from fully opaque
to fully transparent, in contrast to standard binary on/off masks that
only offer fully transparent or fully opaque pixels. An alpha masked
bitmap can capture the effects of anti-aliasing and transparency, so
the colour blending is deferred to when the bitmap is displayed.
Using alpha masks you can create bitmaps with smooth anti-aliased
edges that look good on any background on top of which the bitmap is
displayed. Any areas with flat and graduated transparency blend into
the background under the bitmap. Alpha masked PNGs are particularly
useful for web design and are widely supported, e.g., by NetSurf.
Alpha masked Sprite files are only supported by RISC OS Select3 and
above (which includes the popular RISC OS 4.39 Adjust version).
Many thanks are due to Michael Drake who suggested an elegant method
for computing the required alpha information.
Martin
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