DPI in FOP for images

I know I've seen this before, but I cannot seem to find the style
sheet variable to tweak. Perhaps I'm remembering openjade options for
PostScript output. When FOP generates PDF with in-lined GIF images, it
assumes a DPI of 72. Is there any way to change this value for an
entire document without specifying the scaling values for each
<imagedata> element?

Thanks,

Mike Mascari