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Basic Information on imdiff
Purpose: Shift and expand an image to make it match another.
IMDIFF is a MIRIAD task which finds optimum parameters (in a
maximum likelihood sense) for making one image approximate
another image. The parameters are an amplitude scale factor, dc
offset, shifts in x and y direction and an expansion.
Alternately any of these parameters can be fixed at a given
value, and the others allowed to vary. This task assumes that
the rms noise levels in both images are identical (If this is
not the case then one of the images should be scaled to make it
the case). Also noise in the two images is assumed to be
uncorrelated. If either of these conditions are violated, the
algorithm will not perform optimally when the signal to noise
ratio is poor.
This task is intended to find only small shifts and expansions.
It will probably fail if large shifts and expansions are
present. The task SHIFTY can handle large, integral, shifts.
This task currently only handles a rectangular region of
interest. It does not handle blanked pixels correctly.
The first input image. This is considered to be the "reference"
image. No default.
The second input image. This is considered to be the image that
must be adjusted to make it look like IN1. No default.
This gives the name of an output image data-set, being a version
of second image after adjustment. The default is not to output
an adjusted image.
An output image consisting of the difference between IN1 and the
adjusted form of IN2. It is generally best to look at the
residuals, to check that they are noise-like. The residuals are
Resid(x,y) = In1(x,y)
- Amp*In2(Expand*x+Xshift, Expand*y+YShift)
(Here X and Y are relative to IN2's reference pixel).
The default is not to create the residuals.
The region of interest. Currently this must be a rectangular
region. The default is the entire image.
The task cannot work right to the edge of the image, because the
shifts and expansions might mean that there is no corresponding
point between images near the image edges. Consequently a guard
band is needed. GUARD gives the width of this band, in pixels.
In the output residuals, this band will be set to zero.
Default is 10.
The following five parameters give the initial estimates for the
various parameters that IMDIFF is trying to find. If the
parameters are fixed, then IMDIFF will not change them from
their initial settings.
This gives the initial value, in pixels, of the x-shift.
This should be only +/- a few pixels. Default is 0.
This gives the initial value, in pixels, of the y-shift.
Default is 0.
This gives the initial expansion. Only small expansions can be
handled (e.g. approximately in the range 0.95 to 1.05). This
should be adequate for proper motion studies. Give two values
if you are allowing the x- and y-expansions to vary
independently, one value otherwise. Default is 1.
This gives the initial amplitude scale factor. Default is 1.
This gives the initial dc offset to apply to IN2. The default
Task enrichment options. Minimum match is active. These
determine what to solve for. Possible values are:
noamplitude Do not adjust the amplitude of the second image.
The default is to adjust the amplitude.
nooffset Do not adjust the offset of the second image.
The default is to adjust the offset.
noxshift Do not shift the second image in x.
The default is to optimise the shift in x.
noyshift Do not shift the second image in y.
The default is to optimise the shift in y.
noexpand Do not apply an expansion factor to the second
image. The default is to apply an expansion
factor in y.
expand Expand the x and y axes independently. The
default is that the expansions for the two axes
are the same.
Generated by email@example.com on 21 Jun 2016