For stills I render into bitmap if I'm doing beauty renders (ie not using render layers,) unless I'm rendering in passes in which case I use targas that I then compile in photoshop (make sure there is no camera environment though, or it wont render the background clear.) If you are rendering in passes with empty areas of the shot make sure you render the alpha channels too by checking the appropriate box in the render settings. For animation most people render into IFF and then import the sequence into after effects or fusion (which is a doddle to use btw.) Hope that helps
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