TIFF 6.0 Specification
Final—June 3, 1992
Section 7: Additional Baseline TIFF
Requirements
This section describes characteristics required of all Baseline TIFF files.
General Requirements
Options.
Where there are options, TIFF writers can use whichever they want.
Baseline TIFF readers must be able to handle all of them.
Defaults.
TIFF writers may, but are not required to, write out a field that has a
default value, if the default value is the one desired. TIFF readers must be pre-
pared to handle either situation.
Other fields.
TIFF readers must be prepared to encounter fields other than those
required in TIFF files. TIFF writers are allowed to write optional fields such as
Make, Model, and DateTime, and TIFF readers may use such fields if they exist.
TIFF readers must not, however, refuse to read the file if such optional fields do
not exist.
TIFF readers must also be prepared to encounter and ignore private
fields not described in the TIFF specification.
‘MM’ and ‘II’ byte order.
TIFF readers must be able to handle both byte orders.
TIFF writers can do whichever is most convenient or efficient.
Multiple subfiles.
TIFF readers must be prepared for multiple images (subfiles)
per TIFF file, although they are not required to do anything with images after the
first one. TIFF writers are required to write a long word of 0 after the last IFD (to
signal that this is the last IFD), as described earlier in this specification.
If multiple subfiles are written, the first one must be the full-resolution image.
Subsequent images, such as reduced-resolution images, may be in any order in the
TIFF file. If a reader wants to use such images, it must scan the corresponding
IFD’s before deciding how to proceed.
TIFF Editors.
Editors—applications that modify TIFF files—have a few addi-
tional requirements:
• TIFF editors must be especially careful about subfiles. If a TIFF editor edits a
full-resolution subfile, but does not update an accompanying reduced-resolu-
tion subfile, a reader that uses the reduced-resolution subfile for screen display
will display the wrong thing. So TIFF editors must either create a new reduced-
resolution subfile when they alter a full-resolution subfile or they must delete
any subfiles that they aren’t prepared to deal with.
• A similar situation arises with the fields in an IFD. It is unnecessary—and
possibly dangerous—for an editor to copy fields it does not understand be-
cause the editor might alter the file in a way that is incompatible with the un-
known fields.
No Duplicate Pointers.
No data should be referenced from more than one place.
TIFF readers and editors are under no obligation to detect this condition and
handle it properly. This would not be a problem if TIFF files were read-only enti-
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