Content-type: text/html Manpage of immerge


Section: User Commands (1)
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immerge - Linear merging of images.  




map combination  


IMMERGE is a Miriad task to linearly merge together two images with different resolutions. The two images must be of the same field and use the same coordinate system.

In combining the data, it is assumed that the low resolution image better represents the short spacing data, whereas the high resolution best represents the fine structure. Commonly, the low resolution image will be a single-dish observation, and the high resolution will be a mosaiced interferometric observation.  


This gives the two images to be merged. The first input must be the high resolution image, and the second the low. There is no default. The two images must be on the same coordinate grid. If necessary, use REGRID to achieve this.
The output image. No default.
The flux calibration factor. Ideally the two inputs will have correctly calibrated flux scales, in units like Jy/beam. In this case, the flux calibration factor would be 1. In practise, the calibration may not be perfect, and an extra calibration factor will be required to align the flux scales. "factor" gives the factor to scale the low resolution image to put it on the same flux scale as the high resolution image. Note that this factor is in addition to the scaling needed to convert Jy/beam at a low resolution to Jy/beam at the high resolution.

If no value is given for "factor", IMMERGE determines this by comparing the values in the Fourier plane, of data within an particular annulus (after accounting for the differing resolutions of the two inputs). IMMERGE finds the scale factor which minimises differences between the data of the two (in a robust/L1 sense) in the annulus.

This specifies an annulus, in the Fourier domain, where the high and low resolution images should agree (after allowing for resolution differences). This is the annulus of data used to deduce the flux calibration factor, and with options=feather.

Two or three values can be given. The first two give the inner and outer radius of the annulus in the Fourier domain. The third argument gives the units. Possible units are "klambda" (kilo-wavelengths), "meters", "feet" and "nanoseconds". The default is "klambda".

Values for "uvrange" must be given either if "options=feather" is used or if the flux calibration factor is being deduced.

Region-of-interest parameter. See the help on ``region'' for more information. NOTE: This parameter is ONLY used for determining the flux calibration factor. Only plane selection (e.g. via the ``image'' command) is allowed. Typically you would want to select a range of planes which contains significant signal in the overlap region.
PGPLOT device for a plot. When determining the flux calibration factor, IMMERGE can produce a plot showing the correspondence between the high and low resolution data points in the annulus (after correcting for resolution effects and the deduced flux calibration factor). Ideally it will show a line with "y=x". The default is not to produce a plot. It also plots the difference from this "y=x" line as a function of spatial frequency.
Before Fourier transforming, the images are padded with a guard band. "guard" gives one or two values, being the minimum width of this guard band in pixels, in the x and y directions. The actual guard band used is such that the size of the image plus guard band is a power of 2.
Task enrichment parameters. Several can be given, separated by commas. Minimum match is used.
  normalize  Rather than the output being the merged images, the
             output is the low resolution image corrected by
             the flux calibration factor.
  zero       By default, IMMERGE pads the guard band with data which
             minimizes FFT edge effects. If the input images are
             really zero beyond the edges of the two input images,
             then padding with zeros might be preferable. This is
             particularly so if IMMERGE is deducing the flux
             calibration scale factor.
  feather    This merges the two images together in a fashion similar
             to AIPS IMERG. This method is generally less desirable
             than the default scheme used by IMMERGE.
  shift      Determine the optimum shift to apply to the low
             resolution image to make it align with the high
             resolution one.
  notaper    Normally the low-resolution image is tapered to match any
             residual primary beam response in the high-resolution image.
             This option causes this step to be skipped.




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