NAME

       fiarith - evaluating arithmetic expressions on images as operands

SYNOPSIS

       fiarith [options] "<expression>" [-o|--output <output.fits>]

DESCRIPTION

       The  purpose  of  this  program  is  to evaluate <expression> which is intented to contain
       arithmetic operations and functions on FITS images (of the same  size).  See  the  section
       "Examples" below for examples on the syntax of <expression>

OPTIONS

   General options:
       -h, --help
              Gives general summary about the command line options.

       --long-help, --help-long
              Gives a detailed list of command line options.

       --wiki-help, --help-wiki, --mediawiki-help, --help-mediawiki
              Gives a detailed list of command line options in Mediawiki format.

       --version, --version-short, --short-version
              Gives some version information about the program.

       -o, --output <fits>
              The  name  of  the  output  file (omitting or specifing '-' yields the output to be
              written to stdout).

       -s, --size <sx>,<sy>
              Horizontal and vertical size of  the  output  image  (meaningless  if  <expression>
              contains any existing FITS image).

       -M, --input-mask <fits>
              Input mask file to co-add to output image.

       --output-mask <fits>
              Name of output mask file to create.

       -D, --data <spec>
              Output pixel data format specification.

       -b, --bitpix <bitpix>
              Standard FITS output bitpix value.

       -a, --apply-mask
              Resets pixel values to zero if masked.

       -e, --header <fits>
              Inherit output header from the specified FITS file.

   Available arithmetic operators:
       +      Addition.

       -      Subtraction.

       *      Multiplication.

       /      Division. Dividing by zero yields zero automatically.

   Available arithmetic functions:
       sin(.), cos(.), tan(.)
              Trigonometric functions.

       asin(.), acos(.), atan(.), atan2(.,.), arg(.,.)
              Inverse trigonometric functions.

       abs(.), sq(.), sqrt(.), exp(.), log(.)
              Absolute value, square, Square root, exponential and natural logarithm functions.

   Available image functions:
       min(....)
              The per pixel minimal value of pixel intensities of the images listed (separated by
              comma) in the argument of the function.

       max(....)
              The per pixel maximal value of pixel intensities of the images listed (separated by
              comma) in the argument of the function.

       mean(...)
              The  per  pixel  mean value of pixel intensities of the images listed (separated by
              comma) in the argument of the function.

       norm(.)
              The mean of the pixel values on the image.

       sign(.)
              The per pixel sign function.

       theta(.)
              The per pixel Heaviside step function.

       laplace(.)
              The Laplace transform of the image.

       scatter(.)
              Noise level estimation for the image.

       corr(.,.)
              Correlation between two images.

       smooth(<image>,<sigma>,<size>)
              The smoothed variant of the first argument (threated as an image), which is yielded
              by  the  convolution  with a Gaussian profile with a standard deviation of <sigma>,
              evaluated on a kernel stamp with the size of <size>.

EXAMPLES

       fiarith "'img1.fits'-'orig.fits'" -o diff.fits
              Calculates the per pixel difference between images "img1.fits" and "orig.fits"  and
              stores the result in "diff.fits".

       fiarith -s 512,512 "137.42" -o constant.fits
              Creates  a  new image with the size of 512 by 512 pixels with the constant value of
              137.42.

       fiarith "'-'*26" -o -
              Multiplies the pixel intensities of the image read from the standard  input  by  26
              and  writes  the  result  to the standard output. The "-o -" can either be omitted,
              since by default the output is written to stdout.

       fiarith -s 512,512 "['input.fits'](a/(1-0.3*(X^2-Y^2)))" -o flattened.fits
              This invocation evaluates the "a/(1-0.3*(X^2+Y^2))" expression on each pixel of the
              image "input.fits", where "a" referes to the pixel value itself and X and Y are the
              normalized spatial coordinates. The normalization is always done as X=(2*x-SX)/(SX)
              and  Y=(2*y-SY)/SX,  i.e.  the  X  and  Y coordinates are zero at the center of the
              images, X has a unity absolute value at the left and right edges and  Y  is  scaled
              properly to X.

       fiarith "('R.fits'-'B.fits'-0.5*'D.fits')*(norm('F.fits')/'F.fits')" -o C.fits
              This  operation  performs a simple bias, dark and flat calibration on the input raw
              image "R.fits", expecting "B.fits", "D.fits" and "F.fits" to be  the  master  bias,
              dark  and  flat calibration frames, respectively; and assuming an exposure time for
              the raw image which is the half of the exposure time of the master dark frame.  Due
              to  the  "norm(...)"  function, the mean intensity level of the image is kept to be
              the same as it is in the raw image.

REPORTING BUGS

       Report bugs to <apal@szofi.net>, see also https://fitsh.net/.

COPYRIGHT

       Copyright © 1996, 2002, 2004-2008, 2010-2016, 2018-2020; Pal, Andras <apal@szofi.net>