Content-type: text/html Manpage of imhol


Section: User Commands (1)
Index Return to Main Contents


imhol - Compute amplitude and phase images from real and imaginary  




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).  


Two values; the real and imaginary images, respectively. The imaginary image can be made using the INVERT task 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.
Up to two values; the output intensity image and optionally, its associated error image (which will be constant). Default is no output images.
Up to two values; the output position angle image and optionally, its associated error image (which will not be constant). These will be in degress, radians or microns (see OPTIONS). Default is no output images.
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.
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.
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.
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
  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.




This document was created by man2html, using the manual pages.
Time: 18:35:38 GMT, July 05, 2011