Thumbnail image quality

Hi, I've trawled the posts and can't find anything to help me.
I have an issue with thumbnails for the documents. they don't seem to honour the settings I put in the configuration and are always smaller than I enter. Also the rendered quality is really poor. I guess this is something to do with the upload process combined with the display settings.

It's hard to give you an example because everything is behind a secure site but you probably know what I mean

Any ideas how I can improve the quality?

Just tried to upload an image using ftp and it is better but my customer won't have the facility to do this.

Feature request...auto create thumbnail from uploaded image

Thanks