Hi,
Thanks for the replies, your time is appreciated.
Regarding the maths, I think I was correct (always room for error of course...):
Number of pixels = 4500 * 4500 = 20,250,000
Number of bytes per pixel = 4
4 x 20,250,000 = 81,000,000 bytes
Minimum number of layers required by Pdn = 1 + 2 = 3
3 * 81,000,000bytes = 243,000,000bytes
1024 bytes in a megabyte = 243,000,000bytes / 1024 = 237304.69KB
1024 kilobytes in a Megabyte = 237304.69KB / 1024 = 231.74MB
1024 Megabytes in a Gigabyte = 231.74 / 1024 = 0.23 Gigabytes
For this operation Paint.NET is using approximately 0.23GB
Available physical memory: 1.46 GB
Alongside Paint.net I'll be running Firefox with a couple of open tabs, Windows player and Kaspersky 2013; I usually have system idle processes in the 90% + region.
I will look to increasing memory and installing Windows 7, but given that the maths is correct and the use of other programmes running simultaneously alongside Paint.net is low I find it hard to put this particular problem down to a hardware issue alone.
I don't think a 15cm x 15cm / 4500 x 4500 pixel image is that large, even for my computer.
Any further insights and ideas gratefully accepted.