TIFF 6.0 Specification
Final—June 3, 1992
Run lengths in the range of 0 to 63 pels (pixels) are encoded with their appropriate
Terminating code word. Note that there is a different list of code words for black
and white run-lengths.
Run lengths in the range of 64 to 2623 (2560+63) pels are encoded first by the
Make-up code word representing the run-length that is nearest to, not longer than,
that required. This is then followed by the Terminating code word representing
the difference between the required run-length and the run-length represented by
the Make-up code.
Run lengths in the range of lengths longer than or equal to 2624 pels are coded
first by the Make-up code of 2560. If the remaining part of the run (after the first
Make-up code of 2560) is 2560 pels or greater, additional Make-up code(s) of
2560 are issued until the remaining part of the run becomes less than 2560 pels.
Then the remaining part of the run is encoded by Terminating code or by Make-up
code plus Terminating code, according to the range mentioned above.
It is considered an unrecoverable error if the sum of the run-lengths for a line does
not equal the value of the ImageWidth field.
New rows always begin on the next available byte boundary.
No EOL code words are used. No fill bits are used, except for the ignored bits at
the end of the last byte of a row. RTC is not used.
An encoded CCITT string is self-photometric, defined in terms of white and black
runs. Yet TIFF defines a tag called PhotometricInterpretation that also purports
to define what is white and what is black. Somewhat arbitrarily, we adopt the
following convention:
The “normal” PhotometricInterpretation for bilevel CCITT compressed data is
WhiteIsZero. In this case, the CCITT “white” runs are to be interpretated as
white, and the CCITT “black” runs are to be interpreted as black. However, if the
PhotometricInterpretation is BlackIsZero, the TIFF reader must reverse the
meaning of white and black when displaying and printing the image.
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