AWARE SYSTEMS
TIFF and LibTiff Mail List Archive

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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 17:34 "TIFF LZW : How select predictor", by Gilles Vollant

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?