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Basic Information on 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
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.
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 degrees, 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
Revision: 1.5, 2013/08/30 01:49:21 UTC
Generated by email@example.com on 21 Jun 2016