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    Expand or contract a FITS image using (F)REBIN and update the header


    If the output size is an exact multiple of the input size then REBIN is
    used, else FREBIN is used. User can either overwrite the input array,
    or write to new variables.

Calling Sequence

    HREBIN, oldhd ;Special calling sequence to just update header
    HREBIN, oldim, oldhd, [ newim, newhd, newx, newy, OUTSIZE = ,/SAMPLE,
                            ERRMSG = ]


    OLDIM - the original image array
    OLDHD - the original image FITS header, string array

Optional Inputs

    NEWX - size of the new image in the X direction, integer scalar
    NEWY - size of the new image in the Y direction, integer scalar
            HREBIN will prompt for NEWX and NEWY if not supplied

Optional Outputs

    NEWIM - the image after expansion or contraction with REBIN
    NEWHD - header for newim containing updated astrometry info
            If output parameters are not supplied, the program will modify
            the input parameters OLDIM and OLDHD to contain the new array and
            updated header.

Optional Input Keywords

    /SAMPLE - Expansion or contraction is done using REBIN which uses
              bilinear interpolation when magnifying and boxaveraging when
              minifying. If the SAMPLE keyword is supplied and non-zero,
              then nearest neighbor sampling is used in both cases. Keyword
              has no effect when output size is not a multiple of input size.
    OUTSIZE - Two element integer vector which can be used instead of the
            NEWX and NEWY parameters to specify the output image dimensions
    ALT - Single character 'A' through 'Z' or ' ' specifying which astrometry
          system to modify in the FITS header. The default is to use the
          primary astrometry of ALT = ' '. See Greisen and Calabretta (2002)
          for information about alternate astrometry keywords.

Optional Keyword Output

      ERRMSG - If this keyword is supplied, then any error mesasges will be
              returned to the user in this parameter rather than depending on
              on the MESSAGE routine in IDL. If no errors are encountered
              then a null string is returned.


    The parameters BSCALE, NAXIS1, NAXIS2, CRPIX1, and CRPIX2 and the CD
    (or CDELT) parameters are updated for the new FITS header.


    Compress a 2048 x 2048 image array IM, with FITS header HDR, to a
    724 x 724 array. Overwrite the input variables with the compressed
    image and header.
    IDL> hrebin, im, hdr, OUT = [724, 724]

Procedures Used


Modification History

    Written, December 1990 W. Landsman, ST System Corp.
    Update CD1_1 keywords W. Landsman November 1992
    Check for a GSSS header W. Landsman June 1994
    Update BSCALE even if no astrometry present W. Landsman May 1997
    Converted to IDL V5.0 W. Landsman September 1997
    Use FREBIN to accept sizes that are not a integer multiple of the original
        size W. Landsman August 1998
    Correct for "edge" effects when expanding with REBIN W. Landsman Apr. 1999
    Fixed initialization of header only call broken in Apr 98 change May. 1999
    Remove reference to obsolete !ERR W. Landsman February 2000
    Use double precision formatting for CD matrix W. Landsman April 2000
    Recognize PC00n00m astrometry format W. Landsman December 2001
    Correct astrometry for integral contraction W. Landsman April 2002
    Fix output astrometry for non-equal plate scales for PC matrix or
    CROTA2 keyword, added ALT keyword. W. Landsman May 2005
    Update distortion parameters if present W. Landsman August 2007
    Don't update BSCALE/BZERO for unsigned integer W.Landsman Mar 2008
    Use post-V6.0 notation W. Landsman Nov 2011

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