fmedian HEADAS help file

NAME

fmedian -- Convolve a FITS image with a median value within an user defined rectangular box.

USAGE

        fmedian input output xwindow ywindow

PARAMETERS

infile [string]

Input FITS file and extension number to be convolved with the median filter.

outfile [string]

Output FITS file where the convolved image will be written.

xwindow [integer]

The size of the smoothing window in pixels in the x direction. If not an odd number it will be incremented to nearest odd number.

ywindow [integer]

The size of the smoothing window in pixels in the y direction. If not an odd number it will be incremented to nearest odd number.

(boundary = "nearest") [string]

The algorithm used to compute the values of the out of bounds pixels. The options are:

nearest: Use the value of the nearest boundary pixel.
constant: Use a constant value.
reflect: Generate a value by reflecting around the boundary.
wrap: Generate a value by wrapping around to the opposite side of the image.

(constant = 0.0) [double]

The constant for constant-valued boundary extension.

(datatype = "-") [character]

The data type for the resulting smoothed image. A "-" or " " results in storing the smoothed image with the same data type as the original input image. The letter B or b represents byte, the letter I or i represents short integer, the letter J or j represents integer, the letter E or e represents single precision reals and the letter D or d represents double precision reals.

(nullval = 0.0) [double]

Value to substitute for any undefined pixels within the image.

(copyprime = yes) [boolean]

If true, all of the primary header keywords, the primary array (if any) and all of the extension keywords of the first input file are copied to the output file. If false, only minimal headers are created.

(copyall = no) [boolean]

If true, all other extensions, including the primary array are copied to the output file.

(clobber = no) [boolean]

If true, an existing output file of the same name will be overwritten.

DESCRIPTION

FMEDIAN convolves the FITS image in input with a median value within a rectangular box specified by xwindow, ywindow and places the convolved images in output FITS file. Out of bounds pixels are computed using the algorithm specified by boundary. The FITS image to be smoothed can be in either the primary array or in an image extension. The resulting smoothed image will be placed in either the output files primary array or in an image extension depending on three things; the location of the image in the input file, the value of the copyprime flag and the value of the copyall flag.

If the input image is in the primary array then the resulting image will always be placed in the primary array. In this case, if the copyprime flag is yes then all the keywords from the input primary header will be copied to the output primary header, otherwise only the required keywords will be placed in the output primary header. Setting the copyall flag will cause all the FITS extensions in the input FITS file to be copied over to the output FITS file.

If the input image is in an image extension the the resulting image will be placed in one of three places depending on the values of the copyprime and copyall flags. If the copyprime flag is no the the resulting smoothed image will always appear in the primary array. If the copyall flag is also set then all extension will be copied to the output FITS file and the input primary array will be stored in the image extension that the image was originally stored in the input FITS file. If the copyprime flag is yes then the primary array of the input FITS file will always be copied over to the primary array of the output FITS file. In this case, if the copyall flag is no then the smoothed image will be stored in the first extension of the output FITS file, otherwise the smoothed image will appear in the same extension in both the input and output FITS file and all other extensions will be copied to the output FITS file.

EXAMPLES

1. Convolve an image with a square 3 by 3 box using nearest neighbor boundary extension.

         cl> fmedian image.fits gimage.fits 3 3

2. Convolve an image with a rectangular 3 by 5 box using wrap around boundary extension.

         cl> fmedian img.fits gimg.fits 3 5 bound=wrap

3. Convolve an image in the 3rd extension with a rectangular 7 by 5 box using nearest neighbor boundary extension and store the resulting image in the primary array.

         cl> fmedian imgx.fits[3] gimg.fits 7 5 copyprime=no

BUGS

NOTE: This tool works identically as that of another image smoothing tool

fboxcar. The difference is in the smoothing procedure. In latter case (fboxcar), it is the average value within the rectangular box and for fmedian, it is the median value within the rectangular box.