• REMOVE_BACKGROUND

REMOVE_BACKGROUND

Description

Fit and remove large-scale background variations from images using either KAPPA fitsurface or CUPID findback. See the Starlink documentation (SUN/95 and SUN/255) on both tasks for more information on the parameters shown below. The option exists to mask out a circular region centred on the source before removing the background.

Be aware that the subtraction of the background will add noise (i.e. increase the variance) proportional to the RMS deviation between the image and the background fit.

Creates an output file for each input file with the suffix "_back".

Available recipe parameters

• APERTURE_RADIUS
  • radius of aperture (in arcsec) for masking out source (otherwise 30 arcsec)
• BACKGROUND_FITMETHOD

  • the method for fitting the background, either fitsurface (default) or findback

• FINDBACK_BOX

  • size of box in pixels used by findback for smoothing the image

• FITSURFACE_FITTYPE

  • FITTYPE parameter for fitsurface: polynomial (default) or spline

• FITSURFACE_FITPAR

  • parameters for FITTYPE in fitsurface, up to 2 numbers corresponding to NXPAR/NYPAR for polynomial or KNOTS for spline fit

• FITSURFACE_KEEPSURFACE

  • a flag to request that the surface fitted by fitsurface is kept on disk after processing (1 = yes, 0 = no - default: filename ends "_surface.sdf")

• MASK_SOURCE
  • flag to mask out a circular region on the source before fitting a background (1 = mask out source; 0 = do not mask out source - the default)