Re: Re: GD Watermark Question-

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 -- ------- http://sperling.com/