You can do image sequences. I use PNG, but TGA is available as well. The largest image width is currently 3000 pixels, but I don't think there is a technical reason not to go higher. Of course, you'll need high resolution textures as well. Currently, iClone's max is 8k x 8k. (I've seen 16kx16k mentioned but I have never been able to get to that setting if it exists). This means projects will have a large size, and a GPU with a lot of memory will be good thing.