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FEATHER Algorithm

      FEATHER use the following steps
    - Make oversampled Fourier Transform of both HIGHres and LOWres images
    - Compute the truncation function f(r)
    - Make the Truncated compact Fourier Transform, f(r) x T(LOW)
    - Make the complement long baseline Fourier Transform, (1-f(r)) x T(HIGH)
    - Sum them T(ALL) = R x f(r) x T(LOW) + (1-f(r)) x T(HIGH)
         where is taken from FEATHER_RATIO
    - Make the inverse Fourier Transform
    - Truncate the resulting image to original size and Mask of the HIGHres
      images

    If LOWres is a single-dish image, f(r) should normally be  the  beam  of
    that  telescope to use optimal Signal-to-noise ratio from that data set.
    However, because of pointing errors and other calibration issues such as
    spectral  baseline, using a sharper transition function gives better re-
    sults. FEATHER uses a  exp(-(r/Radius)^Expo) function, where  Radius  is
    taken from FEATHER_RADIUS and Expo from FEATHER_EXPO.


Gildas manager 2023-06-01