TIFF 6.0 Specification
Final—June 3, 1992
Any ASCII field can contain multiple strings, each terminated with a NUL. A
single string is preferred whenever possible. The Count for multi-string fields is
the number of bytes in all the strings in that field plus their terminating NUL
bytes. Only one NUL is allowed between strings, so that the strings following the
first string will often begin on an odd byte.
The reader must check the type to verify that it contains an expected value. TIFF
currently allows more than 1 valid type for some fields. For example, ImageWidth
and ImageLength are usually specified as having type SHORT. But images with
more than 64K rows or columns must use the LONG field type.
TIFF readers should accept BYTE, SHORT, or LONG values for any unsigned
integer field. This allows a single procedure to retrieve any integer value, makes
reading more robust, and saves disk space in some situations.
In TIFF 6.0, some new field types have been defined:
6 = SBYTE
7 = UNDEFINED
8 = SSHORT
9 = SLONG
10 = SRATIONAL
11 = FLOAT
12 = DOUBLE
An 8-bit signed (twos-complement) integer.
An 8-bit byte that may contain anything, depending on
the definition of the field.
A 16-bit (2-byte) signed (twos-complement) integer.
A 32-bit (4-byte) signed (twos-complement) integer.
Two SLONG’s: the first represents the numerator of a
fraction, the second the denominator.
Single precision (4-byte) IEEE format.
Double precision (8-byte) IEEE format.
These new field types are also governed by the byte order (II or MM) in the TIFF
header.
Warning: It is possible that other TIFF field types will be added in the future.
Readers should skip over fields containing an unexpected field type.
Fields are arrays
Each TIFF field has an associated Count. This means that all fields are actually
one-dimensional arrays, even though most fields contain only a single value.
For example, to store a complicated data structure in a single private field, use
the UNDEFINED field type and set the Count to the number of bytes required to
hold the data structure.
Multiple Images per TIFF File
There may be more than one IFD in a TIFF file. Each IFD defines a
subfile.
One
potential use of subfiles is to describe related images, such as the pages of a fac-
simile transmission. A Baseline TIFF reader is not required to read any IFDs
beyond the first one.
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