Basic Information on imhol

Task: imhol
Purpose: Compute amplitude and phase images from real and imaginary
Categories: image analysis

        IMHOL computes amplitude and phase images from real and
        imaginary holographic images.  The amplitude image can be
        debiased, and the phase image is computed as
        atan2(imaginary/real).
 

Key: in
        Two values; the real and imaginary images, respectively.
        The imaginary image can be made using INVERT with
        options=imaginary.  If the (u,v) coordinates for the holography
        data are in arcsec units then the images have units of nanosec
        (the inverse of the usual situation for astronomical imaging).
        Alternatively, the real and imaginary images can be obtained
        from images of the beam pattern using the MIRIAD task FFT.  The
        default units for the axes are in wavelengths.  Wild card
        expansion is supported.

Key: mag
        Up to two values; the output intensity image and
        optionally, its associated error image (which will be constant).
        Default is no output images.

Key: phase
        Up to two values; the output position angle image and
        optionally, its associated error image (which will not be
        constant).  These will be in degrees, radians or microns (see
        'options').  Default is no output images.

Key: sigma
        The mean standard deviation of the noise in the images.
        Required when debiasing or blanking; try to make it as accurate
        a value as possible.  The default is 0.

Key: sncut
        This is the S/N ratio below which the output images
        are blanked (see also options=zero below). It is STRONGLY
        recommended that SNCUT of at least 2 is used.
        The default is 0.

Key: pacut
        The output images are blanked if the error in the phase image
        (degrees, radians or mircrons depending on OPTIONS) is greater
        than this value.  This is active even if you don't output the PA
        image.   Note that there is no equivalent for the output error
        of the POLI image because the error is constant and equal to
        SIGMA.  Keyword SNCUT essentially takes care of this.
        The default is no position angle error based blanking.

Key: options
        Task enrichment options.  Minimum match is active.
          bias    If computing polarized intensity, do NOT remove the
                  Ricean bias in the image.  By default, the bias is
                  removed to first order with
                    P = sqrt(P_obs**2 - sigma**2).
                  You should have a very good reason for using this
                  option.  See VLA memo no. 161 by Patrick Leahy for
                  more details of bias removal.
          zero    When the output pixel is clipped, by setting CLIP(1),
                  setting OPTIONS=ZERO will cause the output polarized
                  intensity image (not the position angle image) pixel
                  to be set to 0.0 rather than being masked out.  This
                  is very important if you are interested in doing
                  statistics on a region of low polarized intensity S/N
                  ratio.  If you leave the region masked rather than
                  zeroed, you will bias the statistics in that region --
                  zero is a better estimate of the pixel than just
                  excluding it from the statistics (provided the clip
                  level is sufficiently small).  Residual bias in the
                  statistical results from the area then depend upon how
                  well the bias remover works and at what level clipping
                  was performed.  See VLA memo no. 161 by Patrick Leahy.
          radians Output the phase image in radians instead of degrees.
          microns Output the phase image as equivalent surface error in
                  microns.
          relax   Only warn about image axis descriptor mismatches
                  instead of giving a fatal error
          bmfit   Fit focus and pointing offsets to aperture E-field
                  maps.
 
Revision: 1.5, 2013/08/30 01:49:21 UTC