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Basic Information on immerge


Task: immerge
Purpose: Linear merging of images.
Categories: map combination

        IMMERGE is a Miriad task to merge linearly 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.

Key: in
        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.

Key: out
        The output image. No default.

Key: factor
        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
        that minimises differences between the data of the two (in a
        robust/L1 sense) in the annulus.

Key: uvrange
        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.

Key: region
        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.

Key: device
        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.

Key: guard
        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.

Key: options
        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
                     that 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 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.
 
Revision: 1.7, 2013/08/30 01:49:21 UTC

Generated by miriad@atnf.csiro.au on 21 Jun 2016