Thanks. I have set it up already.
The images are generated in these resolutions, but they have white borders... the image is like cropped half of the size. Only the bigger image "thickbox_default" is generated properly 1:1 of the size.
Btw. All images i am using are ratio 2:1 ... (height : width )
Here you can see, how it looks. The red arrow shows the bad generated images... I have no idea why is this happening ..