pamtofits(1) - Man pages

Pamtofits User Manual(1) General Commands Manual Pamtofits User Manual(1)

NAME
pamtofits - convert a Netpbm image into FITS format

SYNOPSIS
pamtofits [-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
In addition to the options common to all programs based on libnetpbm
(most notably -quiet, see ]8;;index.html#commonoptions\ Common Options]8;;\ ), pamtofits recognizes the
following command line options:

-min and -max tell pamtofits what "physical values" zero and maxval sam-
ple 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 possible
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 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. Nobody reported
trouble with that until 2008.

However, at least some versions of ImageMagick and Gimp (as seen in
2008) use bottom to top order, so if you use on of these to 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.

Since 2008, people have noted that NASA distributes FITS files with bot-
tom to top order.

HISTORY
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 Pbm-
plus in 1989.