[SOLVED] How to get good resolution in thickbox images?

[iboMonkey]

A question on image-sizes,

I have made changes to both ‘home’ (240×180) and ‘thickbox’ (710×533). Then I uploaded an image again to test it and automatically it got ‘resized’ into an image suitable for home and thickbox. The imagesize of the originally uploaded image is 710×533, in high standard jpg. But look at the picture in thickbox-size (attached)…. It’s nowhere near good to show, even though in reality it didn’t even have to be resized.

What are your experiences with this? Is there a way to improve it? Because this way I could never show my customers.

Kind regards,
ibo

EDIT: I have edited the 'large' setup as well, that was what I should have changed in the first place...