Pamtofits User Manual(0) Pamtofits User Manual(0)
pamtofits - convert a Netpbm image into FITS format
pamtofits [-max f] [-min f] [pamfile]
This program is part of Netpbm(1)
pamtofits reads a PNM or PAM image as input and produces a FITS (Flexible Image Transport
System) file as output. The resolution of the output 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).
-min and -max tell pamtofits what 'physical values' zero and maxval sample values, respec-
tively, 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 corresponding to the Netpbm maxval and the
lowest is that corresponding to Netpbm zero. This isn't really how those cards are sup-
posed to be used, since the input image doesn't necessarily contain the full possible
range of sample values. It is a conservative approximation.
The FITS specification does not specify which data in the file corresponds to which pixel
in the image (i.e. which bytes are the the top left pixel, etc.). Netpbm uses the common
sense, most popular arrangement: 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 generated by pamtofits, it will appear
upside down. To fix that, use pamflip -topbottom on the image before feeding it to
pamtofits 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 Pbmplus in 1989.
fitstopnm(1) , pam(5)
Copyright (C) 1989 by Wilson H. Bent (firstname.lastname@example.org), with modifications by Alberto
netpbm documentation 25 September 2005 Pamtofits User Manual(0)