Fitstopnm User Manual(1) General Commands Manual Fitstopnm User Manual(1)
NAME
fitstopnm - convert a FITS file into a PNM image
SYNOPSIS
fitstopnm [-image=N] [-scanmax] [-printmax] [-min=f] [-max=f] [-omax-
val=N [FITSfile]
Minimum unique abbreviation of option is acceptable. You may use dou-
ble hyphens instead of single hyphen to denote options. You may use
white space in place of the equals sign to separate an option name from
its value.
DESCRIPTION
This program is part of Netpbm(1).
fitstopnm reads a FITS (Flexible Image Transport System) file as input
and produces a PPM image if the FITS file consists of 3 image planes
(NAXIS = 3 and NAXIS3 = 3), or a PGM image if the FITS file consists of
2 image planes (NAXIS = 2), or if you specify the -image option.
Note that the PPM image is highly unlikely to be a true PPM image, as
it is not normal for a FITS image to use the third axis as R, G, and B
components of the pixels. The most common interpretation when there
are 3 axes is that the third one is time. So the image is instead a
pseudo-PPM in which the three sample values of a pixel represent some-
thing other than color components, for example gray levels at three in-
stants (this variation on PPM is common in programs such as fitstopnm
that predate the PAM format).
If you work with FITS images with 3 axes, you should probably always
use the -image option to avoid getting an unwanted pseudo-PPM image.
The program tells you what kind of PNM image it is writing.
OPTIONS
In addition to the options common to all programs based on libnetpbm
(most notably -quiet, see
Common Options ⟨index.html#commonoptions⟩ ), fitstopnm recognizes the
following command line options:
-image=N
This is for FITS files with three axes. This option says that
the third axis is for multiple images, and the option value N
tells which one you want.
-omaxval=N
This is the maxval that the output PNM image is to have.
By default, the maxval is the least possible to retain all the
precision of the FITS input. That means the difference between
the highest and lowest sample value in the input. If the values
range from -5 to 100, for example, the default maxval would be
106 and each PNM sample value would correspond to one FITS sam-
ple value.
For a FITS input with floating point sample values, the preci-
sion is essentially unlimited, so this is not possible. In that
case, the default maxval is simply 255.
This option was new in Netpbm 10.39 (June 2007). Before that,
the output maxval is always the default.
-min=float
-max=float
You can use these options to override the min and max values as
read from the FITS header or the image data if the header has no
DATAMIN and DATAMAX keywords.
-scanmax
Use this option to force the program to scan the data even when
the header has DATAMIN and DATAMAX.
-printmax
With this option, the program just prints the min and max values
and quits without doing its normal job.
This is for use in shell programs. Example:
eval 'fitstopnm -printmax $filename | \
awk {min = $1; max = $2} \
END {print "min=" min; " max=" max}'
NOTES
Pixel Order
You may need to pass the output of fitstopnm through pamflip -topbot-
tom. See pamtofits ⟨pamtofits.html#pixelorder⟩
SEE ALSO
pamtofits(1), pamflip(1), pgm(1)
AUTHOR
Copyright (C) 1989 by Jef Poskanzer, with modifications by Daniel
Briggs (dbriggs@nrao.edu) and Alberto Accomazzi (alberto@cfa.har-
vard.edu).
DOCUMENT SOURCE
This manual page was generated by the Netpbm tool 'makeman' from HTML
source. The master documentation is at
http://netpbm.sourceforge.net/doc/fitstopnm.html
netpbm documentation 02 August 2015 Fitstopnm User Manual(1)
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