[NTG-context] Howto have page size to fit with image size

Hi all, I want to produce a unique metapost image which should be alone on its page and its file, and I want to have a page the size of the image, whichever this size is. I tried this: \setupcolors[state=start] \setuplayout[width=fit,height=fit] \starttext \startuseMPgraphic{dummy} fill fullcircle scaled 5cm withcolor red ; \stopuseMPgraphic \useMPgraphic{dummy} \stoptext But the setuplayout options don't seem to provide what I want. Thank for any hint to have the page size automatically ajust. -- Jean