Difference between revisions of "Feather"

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(Created page with '== Help on feather task: == <pre> Combine two images using their Fourier transforms This algorithm, called feathering, is a simple method for combining two image…')
 
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== Help on feather task: ==
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{{feather}}
<pre>
 
Combine two images using their Fourier transforms
 
 
 
        This algorithm, called feathering, is a simple method for combining two
 
        images with different spatial resolution.  The processing steps are:
 
 
 
              0. regrid the low resolution image to a temporary copy matching the
 
                  high resolution image,
 
              1. transform each image to the gridded visibility plane,
 
              2. sum the gridded visibilities
 
              3. transform back to the image plane.
 
 
 
        The task name comes from the  smooth switching from
 
        one data set to the other using weights assigned according to the
 
        sensitivity of each at any given spatial frequency.  Gaps, if any,
 
        between the spatial frequency ranges are not filled.
 
 
 
        Each image must have a well-defined beam shape (clean beam) for
 
        feathering to work well.  The two images must have the same flux
 
        density normalization scale.
 
 
 
        This task is somewhat experimental and will improve as more experience
 
        with single-dish and interferometric data is obtained over the next few years.
 
 
 
 
 
        Keyword arguments:
 
        imagename -- Name of output feathered image
 
                default: none; example: imagename='orion_combined.im'
 
        highres -- Name of high resolution (interferometer) image
 
                default: none; example: highres='orion_vla.im'
 
            This image is often a clean image obtained from synthesis
 
                observations.
 
        lowres -- Name of low resolution (single dish) image
 
                default: none; example: lowres='orion_gbt.im'
 
            This image is often a image from a single-dish observations
 
                or a clean image obtained from lower resolution synthesis
 
                observations.
 
 
 
        Comments:
 
 
 
            The advantage of feathering is that one does not have to go back to
 
            the visibility data and then image and deconvolve.  It starts with
 
            the high-quality image (with the accurate clean beam).  This is
 
            particularly useful for combining a high-resolution interferometric
 
            image with a lower-resolution single-dish image, although
 
            D-configuration and A-configuration EVLA data can also be combined.
 
            There are often uncertainties in the relative flux density scales
 
            between the two images, and the current implementation of feathers
 
            does not adjustment.
 
 
 
            The clean task also has a method of combining two sets of data with
 
            different resolution.  The high resolution visibility data begins
 
            deconvolution, starting with a modelimage of the lower-resolution
 
            image.  The lower-resolution image must be clean components (or a
 
            sky model), not the low resolution image with its intrinsic
 
            resolution.
 
</pre>
 

Latest revision as of 19:30, 6 May 2015