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TIFF Tag Predictor

IFDImage
Code317 (hex 0x013D)
NamePredictor
LibTiff nameTIFFTAG_PREDICTOR
TypeSHORT
Count1
Default1 (no prediction)

Description

A mathematical operator that is applied to the image data before an encoding scheme is applied.

The general idea is that subsequent pixels of an image ressemble each other. Thus, substracting the information from a pixel that is already contained in previous one, is likely to reduce its information density considerably, and aid subsequent compression.

Theoretically, the predictor step is independent from the compression step, and thus can be combined with any compression scheme. It is, however, likely to be most usefull when combined with either LZW or Deflate compression.

The specification defines these values:

1 = No prediction scheme used before coding.
2 = Horizontal differencing.

A third specification supplement from Adobe, that is not yet available on-line, defines this new value:

3 = Floating point horizontal differencing.

LibTiff defines these values:

PREDICTOR_NONE = 1;
PREDICTOR_HORIZONTAL = 2;
PREDICTOR_FLOATINGPOINT = 3;