Re: resolution in AE

Regarding creating a high-quality still (for publicity or whatever)...

Remember that it will always come back to the assets you use - if they are high resolution to start with, it's POSSIBLE to get a high-resolution output.

So lets say you have a still image (of high resolution) which you have used in your Standard Def comp... you are right that if you just render out a frame from this (even if you use Collapse Transformations) it will still be using the SD resolution, which isn't great.

One option, if ALL your assets are high enough quality, is to make a new comp of a bigger size (you can specify any custom resolution you like) and enlarge it here.
So you could drop your SD comp into a new comp of 2000 x 2000 px (for example) and scale the comp up to fit, then collapse the transformations and the high quality assets will be restored. However, of course any low quality stuff will still be bad. Effects will work with different resolutions so you won't have a problem with those, but you might find some problems with things like particles - if you just scale up the comp, the solid INSIDE the comp is being scaled, so the particles will scale up correctly but start to look bad (as they are being treated like footage). Sometimes hard to get your head around (and I may have even got it wrong just then!) but it's worth pushing on with :)