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?