I'm using Paint Shop Pro. Since I posted, I have been researching this a bit and When I was resizing, I might have been trying to get to a reduced size by resizing an image that had already been reduced, instead of resizing from the original image. I have also discovered the 'preview in web browser' function which gives me a little more control over how the image will appear.
Any other pointers would be appreciated.
2007 E92 328i 6MT (RETIRED)
2009 E90 328i xDrive 6AT (RETIRED)
2014 E84 xDrive 28i 8AT