Thanks for the suggestions!  Qimage Ultimate has actually been compiled with the largeaddressaware flag for years.  If it wasn't, you wouldn't see 2GB in the analyze settings.  The only reason the analyze settings shows 2GB is because it doesn't test anything larger than that: I'll change that in the next version.  When it is changed to read the actual maximum memory, mine shows 2147 MB with additional 1250 MB (on 64 bit Windows).  The problem here is the way Windows manages memory.  When dealing with bitmaps, it needs contiguous memory.  So if you are working with a 1 GB image and you have 3 GB available but the largest contiguous block available is 800 MB, Windows will throw an out of memory error due to the memory fragmentation.  In addition, if you want to load a 1 GB image, you'll need 2 GB of memory to do it reliably because some operations (like filters and even rotations) require an extra copy in memory.

I'll take a look at the thumbnail building but that already has some sophisticated memory management because 4 threads are running at the same time.  You can imagine how difficult it is to manage memory when it is trying to build four 1 GB images at the same time: threads have to be told to wait until memory is available, etc.  But I'll see if I can improve on that.

Regards,
Mike