TIFF 6.0 Specification
Final—June 3, 1992
Section 2: TIFF Structure
TIFF is an image file format. In this document, a
file
is defined to be a sequence of
8-bit bytes, where the bytes are numbered from 0 to N. The largest possible TIFF
file is 2**32 bytes in length.
A TIFF file begins with an 8-byte
image file header
that points to an
image file
directory
(IFD). An image file directory contains information about the image, as
well as pointers to the actual image data.
The following paragraphs describe the image file header and IFD in more detail.
See Figure 1.
Image File Header
A TIFF file begins with an 8-byte image file header, containing the following
information:
Bytes 0-1: The byte order used within the file. Legal values are:
“II”
(4949.H)
“MM” (4D4D.H)
In the “II” format, byte order is always from the least significant byte to the most
significant byte, for both 16-bit and 32-bit integers This is called
little-endian
byte
order. In the “MM” format, byte order is always from most significant to least
significant, for both 16-bit and 32-bit integers. This is called
big-endian
byte
order.
Bytes 2-3 An arbitrary but carefully chosen number (42) that further identifies the file as a
TIFF file.
The byte order depends on the value of Bytes 0-1.
Bytes 4-7 The offset (in bytes) of the first IFD. The directory may be at any location in the
file after the header but
must begin on a word boundary.
In particular, an Image
File Directory may follow the image data it describes. Readers must follow the
pointers wherever they may lead.
The term
byte offset
is always used in this document to refer to a location with
respect to the beginning of the TIFF file. The first byte of the file has an offset of
0.
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