working with PDFs and STDOUT.

Is there a way -- and am I just missing it -- to convert a pdf to an
image format like png on stdout on the fly?
For example I know I can use the following to convert one format to
another and send it to stdout:
$ convert page1.jpg gif:-

but I want to be able to convert just the first page of a pdf to stdout
for displaying thumbnails on the fly.
When I tried the following I received an error.
$convert 3-Ravens.pdf[0] png:-
convert: missing an image filename `png:-'.

Right now my only other option (that I can think of is) to test for the
png thumbnail of page 1 (stored in the same directory) and if it finds
it display it like the rest. If it doesn't find it then create it and
continue.

Any advice would be greatly appreciated!