The difference between sequence output, already available in TG2, and Render to File, is that the latter actually writes image data to the large image file on disk as it's rendered (essentially) rather than keeping a large buffer in memory to write it all to, which is what the normal rendering process does. Because of this large buffer needed for normal rendering - which increases in size proportional to the number of pixels in the image (and sometimes other factors like AA) - the standard rendering process is limited in resolution by available memory. Because TG2 is not yet a 64 bit app, this is more of a problem in practice than it needs to be. Once TG2 x64 is available, the low cost of RAM, and increasing availability of 64 bit OSs will make even the current rendering method much more practical for extremely large images. Still, a render to disk option can be helpful, for example if the render crashes it will usually have what has been rendered so far still there. So you could for example simply do a crop render to finish the remainder. As it is now, with the image being kept in memory until complete, if the render crashes, the image in memory disappears without being written to disk.
So yes, it's an option we'd like to add at some point.
- Oshyan