ThumbsUp sizing problem

I have ThumbsUp running on XServe 10.3.9 and G5 10.4.1.
They use both the same settings, in detail sizing to 400*400 and Quality 90% to generate jpg thumbnails.
The results are completely different on the systems. On the Xserve the image is compressed more with less resolution.
What can i do to get corresponding results?

ThumbsUp uses Quartz to scale/compress images but especially the scaling results are different on Panther or Tiger. I guess there’s no way to fix this as it’s a an OS “feature”.

It works correct with drag&drop, so i think its only a matter of taking parameters from settings.