If an instrument generates only one FITS file per exposure,
is simply a incremental 8digit number with the decimal system.
For example, the
frame_number of the next exposure of
frame_number = 00000100 is
Number of instruments at the Subaru Telescope produce more than one frames per exposure.
In this case, the structure and increment of
frame_number may be instrument-dependent as described below.
HSC produces 116 FITS files (4 of them will not be distributed) per exposure separated into two 58 sequences.
The two last significant digits of
frame_number are used to specify each CCD,
while the third last significant digit is used to distinguish the 58 number sequence.
The first five digit number is also used to identify the exposure as well as the sequence
if it is an even number.
If the first five digit number is an odd number, it indicates the other sequence.
frame_number of HSC is incremented by 200 per exposure.
For the detailed information, please refer the CCD information of the instrument's web site
MOIRCS produces two FITS files corresponding to those taken with channel-1 and channel-2.
These two FITS files are saved separately with odd and even number
corresponding to channel-1 and channel-2, respectively.
Suprime-Cam produces ten FITS files per exposure.
The last significant digit of
frame_number is assigned to specify each CCD.
frame_number of Suprime-Cam, therefore, consists of the first 7 digits to identify the exposure
and the last digit to identify the CCD, and
frame_number is incremented by ten per exposure.
See the CCD information of the instrument's web site for the details.