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2009.01.12 02:51 "Re: Libtiff compression ratios", by Bob Friesenhahn
On Sun, 11 Jan 2009, myopicwatchmaker wrote:
> A typical example: I have a 30,000x6500pixel 8-bit grayscale image which,
> uncompressed occupies 174Mb on disk. Libtiff's deflate algorithm compresses
> this down to a 66Mb file, where Photoshop produces a 48Mb file. I save my
> images in ~8Mb strips, which appears to be the optimum for zip compression.
>
> Does anyone know why libtiff might fail to match Photoshop's compression
> rates? Are there any paramters in libtiff or libzip that might allow
> optimization for humungous images?
These two tags could make a difference:
TIFFTAG_PREDICTOR
PREDICTOR_NONE
PREDICTOR_HORIZONTAL
PREDICTOR_FLOATINGPOINT
TIFFTAG_ZIPQUALITY
The predictor option can arrange to re-organize the data before it is
fed to the compressor so that the data becomes more compressable.
PREDICTOR_HORIZONTAL should be good for continuous tone images.
The quality option specifies the compression "quality" level using
values simlar to gzip (1-9).
I am not sure if these parameters are available for ZIP compression
using 'tiffcp'. The 'tiffcp' manual page does not seem to address ZIP
compression, although it does discuss LZW.
Bob
======================================
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/