In reply to Tall Clare:
I'm always puzzled about resolution measured in Mb, I only understand pixel dimensions! The thing about the Mb thing is that it doesn't refer to the file size of the saved image (the .jpeg), but to the image size "when opened up". If you look around on the screen in your image editor of choice, it may something like 18Mb for an image which was 3Mb in file size. I don't know what it all means!
So I hope someone will explain