[GEM-dev] Alpha channel support

james tittle tigital at mac.com
Thu Mar 17 19:04:28 CET 2005

On Mar 16, 2005, at 5:05 PM, B. Bogart wrote:
> After seeing tom's nice work online I realized I've been missing
> something in Gem. He is using alpha channels in video using Gem on 
> winXP!!

...yeh, nice fish...

> So after this success I went to video. I tried three cases (it seems
> aftereffects only exports videos with alpha channels compressed with
> TIFF, TARGA, and PNG. So for fun I exported alpha channel videos and
> tried to load them in Gem. Every single one loads fine according to the
> pix_film and pix_movie output, BUT only shows a green square in the
> render. Looking further I realized that my Gem 090 does not load any
> quicktime movies compressed with TARGA, TIFF or PNG.

...um, I think you're overlooking the obvious:  green screens == yuv 
processing!  So obviously there are no alpha channels (unless you use 
the gpu alpha blending, like [blend< )...remember, yuv is gem's 
"native" colorspace on osx, but not on the other platforms...in other 
words, you should be in alpha heaven with the above films if you send 
[colorspace RGBA< to [pix_film] or [pix_movie] before loading the 


ps:  otoh, you could always add [pix_rgba] after [pix_film], but this 
will be sloooow...but not for too much longer, as I've been altivec'ing 
the color conversions :-)

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