Feathering is a simple method for combining two images with different spatial resolution.  The processing steps are:

  1. Regrid the low-resolution image to a temporary copy matching the resolution of the high-resolution image,
  2. Transform each image to the spatial-frequency plane (gridded).\
  3. Scale the low-resolution image (uv-grid) by the ratio of the volumes of the two 'clean beams' (high-res/low-res).
  4. Add to this, the uv-grid of the high-resolution image, scaled by (1-wt) where 'wt' is the Fourier transform of the 'clean beam' defined in the low-resolution image.
  5. Transform back to the image plane.

Both input images must have a well-defined beam shape for this task to work.  This could be a 'clean beam' for interferometric images, and a 'primary-beam' for a single-dish image.

The two images must also have the same flux density normalization scale.

    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
        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
         sdfactor -- value by which to scale the Single Dish image. Default is 1.0
                         Basically modifying the flux scale of the SD image
     effdishdiam -- New effective SingleDish diameter to use in m. Obviously one can only reduce the dish effective dish diameter in feathering. Default -1.0 means leave as is.
     lowpassfiltersd -- If True the high spatial frequency in the SD image is rejected.
                                   Any data outside the maximum uv distance that the SD
                                   has illuminated  is filtered out.


This task can be used as one method of combining single-dish and interferometric images after they have been separately made.

The clean task allows another method of combining single-dish and interferometric data. The single-dish image can be used as a starting model for the interferometric image-reconstruction. If there is some overlap between the spatial-frequencies contained in the single-dish image and the interferometer sampling function, then, such a starting model will help constrain the solutions on the short-baselines of the interferometric data.