At 12:32 PM -0400 9/19/10, TR Shaw wrote:
On Sep 19, 2010, at 11:50 AM, tedd wrote:
At 12:36 AM +0100 9/18/10, Ashley Sheridan wrote:
I know this is getting a little off-topic here, but surely the way a
jpeg destroys data in an image would destroy the stenography information
too? To the human eye all would appear normal, but the copyright info
would be lost?
I don't know much about this sort of thing, so I'm making assumptions
here.
It's the difference between lossless and lossy compression. The
first meaning no loss in data and the second is loss of data. PNG
and jpeg is lossless whereas gif is lossy.
Actually GIF is lossless (it uses LZW encoding) PNG is also lossless
(Ii uses DEFLATE). The specification for JPEG supports both lossy
and lossless. And then, of course there is wavelet used in JPEG2000
and other wavelets These are lossy.
Tom
Aahh...
I stand corrected.
My statement was from my experience of taking images (i.e., jpeg/png)
and then creating GIF's from them where the process was lossy. The
process took the entire palette of colors provided by jpeg/png and
then picked the "best" 256 colors to create the image, which is no
question lossy. However, the data compression technique to create the
GIF was not lossy.
My bad.
Cheers,
tedd
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