XVista manual page

NAME

sky - determines sky level in an image file

SYNOPSIS

sky source_file [box=] [circle=] [pix=] [quiet]

DESCRIPTION

This routine computes the "sky" level under the assumption that it is the most common pixel intensity (i.e. the mode). The routine calculates the histogram of the source_file in the command line determines the adu value at which the histogram is a maximum (the mode). No interpolation or fitting is done to determine a maximum than the nearest integer value.

Note: the minimum sky value is 0.

The rms fluctuations of the sky are determined by fitting a gaussian to the histogram. The rms value of this value is called skysig.

The box option restricts the sky calculation to the specified BOX number.

If pix=n is specified, only every n'th pixel is used to calculate the sky value, which speeds up execution times.

Nothing (not even warning messages) is printed if the quiet flag is given, but the values of the SKY and SKYSIG variables are set.

EXAMPLE

sky crab - computes the sky value for the file `crab.fts' using the entire file.

sky alpha box=2 pix=16 - computes the value of the sky within box 2 of the file `alpha.fts', Only every 16'th pixel is used in computations.

SYMBOLS

sky, skysig