TIFF 6.0 Specification
Final—June 3, 1992
Section 10: Modified Huffman Compression
This section describes TIFF compression scheme 2, a method for compressing
bilevel data based on the CCITT Group 3 1D facsimile compression scheme.
References
• “Standardization of Group 3 facsimile apparatus for document transmission,”
Recommendation T.4, Volume VII, Fascicle VII.3, Terminal Equipment and
Protocols for Telematic Services, The International Telegraph and Telephone
Consultative Committee (CCITT), Geneva, 1985, pages 16 through 31.
• “Facsimile Coding Schemes and Coding Control Functions for Group 4 Fac-
simile Apparatus,” Recommendation T.6, Volume VII, Fascicle VII.3, Termi-
nal Equipment and Protocols for Telematic Services, The International
Telegraph and Telephone Consultative Committee (CCITT), Geneva, 1985,
pages 40 through 48.
We do not believe that these documents are necessary in order to implement Com-
pression=2. We have included (verbatim in most places) all the pertinent informa-
tion in this section. However, if you wish to order the documents, you can write to
ANSI, Attention: Sales, 1430 Broadway, New York, N.Y., 10018. Ask for the
publication listed above—it contains both Recommendation T.4 and T.6.
Relationship to the CCITT Specifications
The CCITT Group 3 and Group 4 specifications describe communications proto-
cols for a particular class of devices. They are not by themselves sufficient to
describe a disk data format. Fortunately, however, the CCITT coding schemes can
be readily adapted to this different environment. The following is one such adap-
tation. Most of the language is copied directly from the CCITT specifications.
See Section 11 for additional CCITT compression options.
Coding Scheme
A line (row) of data is composed of a series of variable length code words. Each
code word represents a run length of all white or all black. (Actually, more than
one code word may be required to code a given run, in a manner described below.)
White runs and black runs alternate.
To ensure that the receiver (decompressor) maintains color synchronization, all
data lines begin with a white run-length code word set. If the actual scan line
begins with a black run, a white run-length of zero is sent (written). Black or white
run-lengths are defined by the code words in Tables 1 and 2. The code words are
of two types: Terminating code words and Make-up code words. Each run-length
is represented by zero or more Make-up code words followed by exactly one
Terminating code word.
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