On Tue, Feb 18, 2003 at 02:21:13PM +1300, Helmut Walle wrote:
> Gifblast
> normally gave me a size reduction between 10 and 30 percent - yes,
> well, not that much, but as I said, for already compressed data.
indeed that is quite impressive actually.
> Re images, there is one more trick: true colour images need much more
> space than indexed ones. This is practically quite useful for images
> not requiring more than 256 different colours (you probably don't want
> to do this to your photos!). GIMP offers a hot-key (Alt-i) for
> converting RGB true colour to indexed format. From the point of view
> of information theory, this is also a data compression, and it is
> lossless if the number of colours you choose for the indexed file is
> equal or greater than the number of colours in the original.
hmm, doesn't png do this automaticly?
ie save a file with the least number of bits possible to display all the
colors?
i remember (but i could be mistaken) that converting some gif to png
gave a considerable savings because the gif only had a few colors abd
png would save them with 4 bits or less instead of 8 (which would be
a 50% saving)
> Enough lecturing for now :-) One final question: is anyone aware of a
> simple tool for Linux / Unix that calculates the theoretical
> compression limit for a file? Would just be interesting to check how
> good or bad the compression software really does...
such a calculation should actually be built right into gzip and bzip2... :-)
greetings, martin.
--
interested in doing pike programming, sTeam/caudium/pike/roxen training,
sTeam/caudium/roxen and/or unix system administration anywhere in the world.
--
pike programmer working in europe csl-gmbh.net
open-steam.org (www.archlab|(www|db).hb2).tuwien.ac.at
unix bahai.or.at iaeste.(tuwien.ac|or).at
systemadministrator (stuts|black.linux-m68k).org is.(schon.org|root.at)
Martin B�hr http://www.iaeste.or.at/~mbaehr/
