Next: Data Records
Up: The Image Extension
Previous: The Image Extension
The image extension follows the rules for required keywords in extensions
stated in section 3.3.2. The first keywords
of a FITS image extension header, through GCOUNT, must appear
consecutively in the order listed below.
- 1.
- XTENSION (character) has the value
'IMAGE'
for image extensions.
- 2.
- BITPIX (integer) provides the number of bits per ``pixel'' value.
The values allowed are the same as those for the primary data array.
- 3.
- NAXIS (integer) is, for an image extension, the number of axes
in the extension data array. A value of zero is acceptable and indicates that
no data are associated with the current header. The maximum possible value
is 999. Negative values are not allowed.
- 4.
- NAXISn, NAXIS (NAXIS=0 -> NAXIS1
not present) (integer) is the number of elements along axis n
of the array. The NAXISn keywords in an image extension
are governed by the same rules as those in a primary header.
- 5.
- PCOUNT (integer) has the value 0 for image extensions.
- 6.
- GCOUNT (integer) has the value 1 for image extensions.
(...the other keywords follow until...)
END (no value) The last keyword must be END. This
card image has no ``='' in column 9 or value field but is filled
with ASCII blanks.
The remainder of the last header record should be filled with ASCII
blanks.
Note that while the rules for generalized extensions do not specify where
the PCOUNT and GCOUNT keywords are located between the
last NAXISn and the END keywords, the image extension
rules require that they appear immediately after the last
NAXISn card image.
Next: Data Records
Up: The Image Extension
Previous: The Image Extension