Pamtofits User Manual(0) Pamtofits User Manual(0)NAMEpamtofits - convert a Netpbm image into FITS format
SYNOPSISpamtofits [-max f] [-min f] [pamfile]
DESCRIPTION
This program is part of Netpbm(1).
pamtofits reads a PNM or PAM image as input and produces a FITS (Flexi‐
ble Image Transport System) file as output. The resolution of the out‐
put file is either 8 bits/pixel, or 16 bits/pixel, depending on the
value of maxval in the input file. If the input file is a PBM or PGM
image, the output file consists of a single plane image (NAXIS = 2). If
instead the input file is a PPM image, the output file will consist of
a three-plane image (NAXIS = 3, NAXIS3 = 3).
OPTIONS-min and -max tell pamtofits what 'physical values' zero and maxval
sample values, respectively, in the input image represent. Physical
values are a FITS concept. pamtofits sets up the BSCALE and BZERO FITS
header cards to indicate this information.
The default for -min is 0 and for -max is the maxval, which means if
you don't specify these options, the FITS physical values are in fact
the original Netpbm sample values.
pamtofits always sets up the FITS header DATAMIN and DATAMAX cards to
indicate that the highest physical value in the image is the one corre‐
sponding to the Netpbm maxval and the lowest is that corresponding to
Netpbm zero. This isn't really how those cards are supposed to be
used, since the input image doesn't necessarily contain the full possi‐
ble range of sample values. It is a conservative approximation.
NOTES
Pixel Order
The FITS specification does not specify which data in the file corre‐
sponds to which pixel in the image (i.e. which bytes are the the top
left pixel, etc.). Netpbm uses the common sense, most popular arrange‐
ment: row major, top to bottom, left to right. That means in a 10 wide
by 20 high image, the first 10 pixels in the file are the top row and
the last 10 are the bottom row. Within each row, the first pixel is
the leftmost one and the last pixel is the rightmost one.
Netpbm has always done that, since it first understood the FITS format
in 1989, so it is something of a de facto standard.
However, at least some versions of ImageMagick and Gimp (as seen in
2008) use bottom to top order, so if you use display a FITS image gen‐
erated by pamtofits, it will appear upside down. To fix that, use pam‐
flip -topbottom on the image before feeding it to pamtofits.
HISTORYpamtofits was originally pnmtofits and did not handle PAM input. It
was extended and renamed in Netpbm 10.30 (October 2005).
pnmtofits was itself an extension of pgmtofits, which was added to Pbm‐
plus in 1989.
SEE ALSOfitstopnm(1), pam(1)FITS(1)AUTHOR
Copyright (C) 1989 by Wilson H. Bent (whb@hoh-2.att.com), with modifi‐
cations by Alberto Accomazzi (alberto@cfa.harvard.edu).
netpbm documentation 25 September 2005 Pamtofits User Manual(0)
