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1999.08.22 17:34 "TIFF LZW : How select predictor", by Gilles Vollant
1999.08.22 18:59 "RE: TIFF LZW : How select predictor", by Gilles Vollant

1999.08.22 18:59 "RE: TIFF LZW : How select predictor", by Gilles Vollant

Tiff 6.0 doc say
<<

LZW without differencing works well for 1-bit images, 4-bit grayscale images,

and many palette-color images. But natural 24-bit color images and some 8-bit

grayscale images do much better with differencing.>>

So Adobe Photoshop does like Adobe Tiff Spec

-----Message d'origine-----

De: owner-tiff@olympiakos.com [mailto:owner-tiff@olympiakos.com]De la part de Gilles Vollant

Envoyé: dimanche 22 août 1999 19:35
À: tiff@olympiakos.com
Objet: TIFF LZW: How select predictor

Sometime LZW compressed TIFF are smaller with Predictor=1 (or none Predictor
Tag, 1 is the default value), sometime with Predictor=2

Tiff spec say:
<<
A predictor is a mathematical operator that is applied to the image data
before an
encoding scheme is applied. Currently this field is used only with LZW
(Com-pression=
5) encoding because LZW is probably the only TIFF encoding scheme
that benefits significantly from a predictor step. See Section 13.
The possible values are:
1 = No prediction scheme used before coding.
2 = Horizontal differencing.
Default is 1.>>

Photoshop seem saved Paletted image with predictor 1, and RGB or grey image
with predictor 2

Any tips?