not much harder than doing a file writer for png. Maya will supply you with the color info of each pixel as floatimg point.
Why, do you need that? I mean its as fast to render out as iff and convert them to png, after all thats what may would do because youd need to wait till the entire picture is ready! But doing afloating point format would be much more productive.
Also if the size is an issue (hardly ever) then do it on per frame basis.
