2009.01.13 22:11 "Re: [Tiff] Libtiff compression ratios", by Frank Warmerdam
Setting TIFFTAG_PREDICTOR to PREDICTOR_HORIZONTAL worked beautifully. With the predictor running, libtiff's compression ratios reach parity with Photoshop.
Increasing the deflate compression ratio to its maximum via TIFFTAG_ZIPQUALITY had only marginal effects on compression (a 2% improvement) while tripling the computation time required.
I appreciate the advice! Perhaps PREDICTOR_HORIZONTAL might make a good default value for the libtiff predictor tag?
Nick,
A case could be made for it being the default, though there are types of images that it would perform poorly or at least with no improvement, for.
I am however not inclined to change stuff like this without careful consideration and the impacts are not too clear to me.
Best regards,
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I set the clouds in motion - turn up | Frank Warmerdam, warmerdam@pobox.com
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