2009.01.12 01:19 "[Tiff] Libtiff compression ratios", by myopicwatchmaker

2009.01.12 02:51 "Re: [Tiff] 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/