NYCPHP Meetup

[putamare]

On Jun 25, 2004, at 1:58 PM, Chris Bielanski wrote:

>  but I coulnd't tell you what LZW actually is,

Short explanation is that it changes a stream of data like 000000111000 
etc. into 6x0,3x1,3x0 etc. (then represents it again in binary), which 
is usually shorter than the original stream. Note that encoding for 
10101010101010101010101 etc. would actually be longer, but that isn't a 
very common pattern...

> or how it applies to GIF formatting.

As far as I can remember (but I can easily be wrong as I didn't care at 
the time, nor do I now), the patent issues (more than you'll want to 
know about that here:
http://cloanto.com/users/mcb/19950127giflzw.html
), is that the patent restrictions apply to encoding, but not decoding, 
thus Software like Photoshop has to pay a licensing fee, but browsers 
like mozilla don't.

> Also, how does PNG compress itself without using LZW?

More than you ever wanted to know about png:
http://www.libpng.org/pub/png/

& How PNG's Two-Dimensional Interlacing Works
http://www.libpng.org/pub/png/pngpics.html



jeff.knight not junkmail at nyphp.org