I have a trac Page with 4 images.
[root@s100 ~]# ls -l /srv/trac/psuc/attachments/wiki/BilderDoku/ -h
total 728K
-rw-r--r-- 1 apache apache 191K 2009-04-29 20:06 2009042....jpg
-rw-r--r-- 1 apache apache 175K 2009-04-29 20:12 20090429...f.jpg
-rw-r--r-- 1 apache apache 162K 2009-04-29 20:05 20090429...t.jpg
-rw-r--r-- 1 apache apache 179K 2009-04-29 20:04 verf...keit.jpg
Exporting this page as pdf results in a 17MB pdf.
I reproduced this on the commandline.
[root@s100 ~]# htmldoc test.html --jpeg=90 --format pdf14 --webpage -f jpeg.pdf
PAGES: 4
BYTES: 1217910
[root@s100 ~]# htmldoc test.html --format pdf14 --webpage -f raw.pdf
PAGES: 4
BYTES: 17382511
[root@s100 ~]# ll jpeg.pdf raw.pdf -h
-rw-r--r-- 1 root root 1.2M 2009-04-30 12:52 jpeg.pdf
-rw-r--r-- 1 root root 17M 2009-04-30 12:54 raw.pdf
I'd suggest to add the --jpeg option by default.