Re: filmscanners: Scanning and memory limits in Windows

[TonySleep@halftone.co.uk (Tony Sleep)]

On Sun, 29 Jul 2001 01:10:13 +0100  Steve Greenbank 
(steve@gccl.fsbusiness.co.uk) wrote:

> I have not checked but  I suspect lossless is actually very nearly 
> lossless.
> i.e. there are some rounding errors from the compression algorithms.

Shouldn't be, in the ZIP/LZW type compression found in compressed TIFF's - 
all that does is replace recurring patterns of byte values with a single 
character, and a code table so it can reconstitute the original

eg, with the first line quoted above

*=I[space]
^=ly
$=lossless

> *have not checked but *suspect $ is actual^ very near^ 
> $.

I believe that LZW algorithms vary in their thoroughness (eg, how big the 
buffer they use to find patterns), which is why some compress more than 
others. Speed differences are common too. But you should get out what went 
in otherwise it's broken.

I don't know if the LZW scheme for TIFF's is fixed or not, but PS shoves 
all sorts of stuff in TIFF headers (IPTC info, ICM tag, thumbnail etc)


Regards 

Tony Sleep
http://www.halftone.co.uk - Online portfolio & exhibit; + film scanner info 
& comparisons