How to fill a DVD

[Shirley Kehr]

On a DVD that had a 26-minute movie and a couple slide shows, only about
half the disk was used (as determined by turning it over and looking at
the color change).

I really wanted another slide show on the DVD, but didn't know if there
would be enough room. In this case, should I have assumed that the movie
would fill about 2 GB and then add up the original file sizes of the
slides to see how many I could fit in the other 2 GB?

Or, does iDVD compress the slides so that they don't take up anything
close to their original sizes?

Shirley