[Plugin: NextGEN Gallery] rounded corners with gd library

Dear Nextgen people,

Is there a way to generate rounded corners (with the GD library), i know how but where can i find the configuration parameters in the nextgen plugin. I need to add:
'fltr[]=ric|10|10','f=png'

But where?!

Thanks!!

http://ww.wp.xz.cn/extend/plugins/nextgen-gallery/