fitstopnm - convert a FITS file into a PNM image


fitstopnm [-image=N] [-scanmax] [-printmax] [-min=f] [-max=f] [-omaxval=N [FITSfile]

Minimum unique abbreviation of option is acceptable. You may use double 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.


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.

The program tells you what kind of PNM image it is writing.


 This is for FITS files with three axes. The assumption is that the third axis is for multiple images, and this option lets you select 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 sample value.

For a FITS input with floating point sample values, the precision 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.


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.

 Use this option to force the program to scan the data even when the header has DATAMIN and DATAMAX.

 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}’


Pixel Order

You may need to pass the output of fitstopnm through pamflip -topbottom. See pamtofits


pamtofits(1) , pamflip(1) , pgm(5)



Copyright (C) 1989 by Jef Poskanzer, with modifications by Daniel Briggs ( and Alberto Accomazzi (

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