AWARE SYSTEMS
TIFF and LibTiff Mail List Archive

Thread

2006.03.04 03:05 "[Tiff] LZW Compression with 16-bit TIFF", by Frank Peters
2006.03.04 03:12 "Re: [Tiff] LZW Compression with 16-bit TIFF", by Bob Friesenhahn
2006.03.04 03:33 "Re: [Tiff] LZW Compression with 16-bit TIFF", by Frank Peters
2006.03.04 06:27 "Re: [Tiff] LZW Compression with 16-bit TIFF", by Bob Friesenhahn
2006.03.04 12:21 "Re: [Tiff] LZW Compression with 16-bit TIFF", by Joris

2006.03.04 06:27 "Re: [Tiff] LZW Compression with 16-bit TIFF", by Bob Friesenhahn

On Fri, 3 Mar 2006, Frank Peters wrote:

16 bit data can be difficult to compress. Have you tried enabling horizontal differencing?

   TIFFSetField(tiff,TIFFTAG_PREDICTOR,2);

Why should 16-bit data be any different in principle that 8-bit data? A change in data length should not have any bearing on compression (at least that's what I would first think).

The more levels available, the more difficult the data is to compress. That is due to less opportunity for repeated codes.

As for horizontal differencing, supposedly that's what the "-c lzw:2" option accomplishes. Is there another way to enable this by setting some parameter in the source code and then recompiling?

The line of code that I posted? :-)

Bob
======================================
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/