🚀 go-pugleaf

In article <1992Aug13.215318.530@ms.uky.edu> soward@slow.inslab.uky.edu  
(John Soward) writes:
> Glenn Reid writes
> -> the compressed data.  Just yesterday I got a 10-to-1 compression
> -> on a directory full of TIFF files, and I thought that TIFF already
> -> had reasonably good compression in its internal format!
> 
> 	No actually it sucks (e.g it has none)...unless you are using one  
of  
> NeXTs TIFF compression schemes...which are lempel-ziv (same as compress)  
or  
> JPEG (radically diferrent and results in a huge compression, but is  
"lossy" --  
> which sometimes is a big deal and sometimes is not).
> --

This is incorrect information.
TIFF 5.0 has optional compression of various types.
   LZW --   same as in compress. Previous substrings in a lookup table.
   packbits --  run length encoding
   group 4? fax compression. -- Various bit strings representing runs of
                              0 and 1 bits. Some interline deltas.

NXImageBitImageRep supports LZW and packbits.

The JPEG data in 2.x TIFF files is a non-standard extension because it had  
not yet been addressed in TIFF when 2.0 shipped. JPEG will be part of TIFF  
6.0.  3.0 NeXTStep is supposed to conform to TIFF 6.0.

For the most part LZW and packbits do very well on non-continous tone  
images. Maybe not state of the art but certainly some big savings.


	-greg.





-- 
Greg Cockroft                       greg@agog.com    
Agog, Inc.                          (517) 627-2186   fax 2673
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Grand Ledge, MI  48837