image-requirements for lightweight PDF?

I'm producing a print book with createspace using docbook. My FO
images are 300 dpi, but I want to make an ebook available -- either a
PDF or epub file.


When I convert to epub format, I'll be keeping 96 dpi images at 63K as
png with a file reference for  the role ="epub-graphic.png."

I was wondering. If I created another role (role="web-pdf"), what kind
of image requirements would be recommended? would the epub-graphic
version be sufficient for a web-pdf?

It would seem cumbersome to sell  the PDF for printing to consumers
when the FO version  could easily get to 30  MB. And it would be
convenient if I could use the images with epub-role for web-pdfs? Any
thoughts or recommendations? Could I use the same asset when making a
lightweight PDF as well as an ebook?



-- 
Robert Nagle