Sachin Garg wrote:
There are a number of tools available which can do "lossless"
compression of jpeg files, they get around 20-25% compression. There
are both commercial/proprietary (StufIt) and free/open-source options
(PackJPG, PAQ etc...).

Have you tried any such tool? Do you use any?

I am in process of publishing an image compression benchmark and want
to know what is in actual popular use and what all is only
academically interesting.

And if not, then why not? what do you think is missing in them that
would make you change your mind?

Sachin Garg [India]
www.sachingarg.com | www.c10n.info

JPEG and 'losless' are really mutually exclusive terms.
The whole idea of JPEG compression is to achieve high compression rates
(6:1 or better), by discarding information not required for satisfactory
image quality, and then applying a standard compression technique, such
as LZW with Huffman, to the result. Leaving out the lossy step results
in dramatically reduced compression. Not worth bothering with.