Large Images - Crashes?

I’m doing poster artwork with blender and I keep getting crashes during compositing. I’m running Ubuntu Studio 64 bit, and I have 8GB of RAM. I figure the problem is something to do with RAM, and adding more would help. Are there any tricks for dealing with large images, or is it just a RAM upgrade?
Thanks in advance,

There are limits, I believe that Blender could not work with the full 4k frames in Tos while compositing too. I haven’t had much luck when processing large RAW images either, unless scaled.