Combine two images using their Fourier transforms
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
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.
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.
showplot -- If True will plot the cuts across the feathring function
Comments:
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.
1.8.0