Transparent background in AfterEffects?

[londonweb]

I need to export an image sequence from AfterEffects with a transparent background. I'm trying to do it as PNG (but anything will do really), the problem is that when I go to the output settings, 'Millions of Colours+' and the other options indicating an alpha channel for transparency are greyed out.

I'm sure it's a simple fix but I've not used AE for a while and can't think what I might have missed.

 

[londonweb]

Don't worry, found the problem- there's an option just above the colour depth that lets you specify rgb or rgb + alpha.