TIFF 6.0 Specification
Final—June 3, 1992
a.
b.
TIFF FillOrder (tag 266) should always be explicitly specified.
FillOrder = 1 should be employed wherever possible in persistent material
that is intended for interchange. This is the only reliable case for widespread
interchange among computer systems, and it is important to explicitly con-
firm the honoring of standard assumptions.
FillOrder = 2 should occur only in highly-localized and preferably-transient
material, as in a facsimile server supporting group 3 facsimile equipment.
The tag should be present as a safeguard against the CCITT encoding “leak-
ing” into an unsuspecting application, allowing readers to detect and warn
against the occurence.
c.
There are interchange situations where fill order is not distinguished, as when
filtering the CCITT encoding into a PostScript level 2 image operation. In this
case, as in most other cases of computer-based information interchange,
FillOrder=1 is assumed, and any padding to a multiple of 8 bits is accomplished
by adding a sufficient number of 0-bits to the end of the sequence.
Strips and Tiles.
When CCITT bi-level encoding is employed, interaction with
stripping (Section 3) and tiling (Section 15) is as follows:
a.
Decompose the image into segments—individual pixel arrays representing
the desired strip or tile configuration. The CCITT encoding procedures are
applied most flexibly if the segments each have a multiple of 4 lines.
Individually encode each segment according to the specified CCITT bi-
level encoding, as if each segment is a separate raster-graphic image.
b.
The reason for this general rule is that CCITT bi-level encodings are generally
progressive. That is, the initial line of pixels is encoded, and then subsequent lines,
according to a variety of options, are encoded in terms of changes that need to be
made to the preceding (unencoded) line. For strips and tiles to be individually
usable, they must each start as fresh, independent encodings.
Miscellaneous features.
There are provisions in CCITT encoding that are mostly
meaningful during facsimile-transmission procedures. There is generally no sig-
nificant application when storing images in TIFF or other data interchange for-
mats, although TIFF applications should be tolerant and flexible in this regard.
These features tend to have significance only when facilitating transfer between
facsimile and non-facsimile applications of the encoded raster-graphic images.
Further considerations for fill sequences, end-of-line flags, return-to-control (end-
of-block) sequences and byte padding are introduced in discussion of the indi-
vidual encoding options.
T4Options
Tag
= 292 (124.H)
Type = LONG
N
=1
See Compression=3.
This field is made up of a set of 32 flag bits. Unused bits
must be set to 0. Bit 0 is the low-order bit.
Bit 0 is 1 for 2-dimensional coding (otherwise 1-dimensional is assumed). For
2-D coding, if more than one strip is specified, each strip must begin with a 1-
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