Default 640*480 perhaps just interpolated or compression very high?

:?

Hello,
i find photos made by the xda II at a resolution of 640*480 have visible artefacts. Photos at 320*240 don't have them that strong. That makes me think that the 640*480 might just be interpolated?!

Or is the compression too high? Is it possible to change the strength of the compression?

thanx