creating a small iso image from a CD

How do you get the iso image of a CD without copying all the unused
data space? If you use readcd or dd, you always get an iso image of
about 650MB, even if the CD contains less than a MB. While you can limit
the number of sectors or blocks, apparently this cannot be done in the
obvious way:

% df
/dev/cdrom 292954 292954 0 100% /mnt/cdrom
% readcd sectors=0-144 f=isofs.img
% ls -l isofs.img
-rw-r--r-- 1 root root 294912 Aug 11 18:17 isofs.img

While the image is big enough, it is incomplete (readable, but some
files are missing).

It seems obvious that somewhere in the OS there is code that knows exactly
how to read only the necessary data, but is there an application that
uses that to simply copy the minimum size image?

Thanks,
Marcel van der Goot
<vdgoot@earthlink.net>