Imaging Backend Selection

Overview

Karabo supports multiple imaging backends while migrating from RASCIL-based imaging to SKA-SDP imaging. For reproducible workflows, pass the backend explicitly in code rather than relying on environment defaults.

For backend-switched imaging, use:

  • karabo.imaging.imager_factory.ImagingBackend

  • karabo.imaging.imager_factory.get_imager

  • karabo.imaging.imager_interface.ImageSpec

Current default backend

If you do not explicitly choose a backend, Karabo uses sdp by default.

The default is resolved in parse_imaging_backend via:

  • environment variable IMAGING_BACKEND when set

  • fallback to ImagingBackend.SDP otherwise

How to select a backend

  1. In Python code (recommended for reproducibility):

from karabo.imaging.imager_factory import ImagingBackend, get_imager
from karabo.imaging.imager_interface import ImageSpec

imager = get_imager(ImagingBackend.SDP)  # or RASCIL / WSCLEAN
spec = ImageSpec(npix=1024, cellsize_arcsec=1.0, phase_centre_deg=(20.0, -30.0))
dirty, psf = imager.invert(vis, spec)
restored = imager.restore(dirty, psf)

  1. Via environment variable:

export IMAGING_BACKEND=sdp   # or rascil / wsclean

  1. Via CLI flag in entry points that expose it (for example):

python karabo/performance_test/time_karabo_reconstruction.py --imaging-backend sdp

Behavior notes

  • ImagingBackend.SDP: - invert uses the SDP imaging path. - restore runs SDP deconvolution + restore.

  • ImagingBackend.RASCIL: - Deprecated legacy backend. Selecting it emits a deprecation warning. - invert uses the RASCIL adapter path. - restore runs the legacy RASCIL cleaning workflow. The adapter reuses the

    visibility from the previous invert call because RASCIL cleaning does not consume an existing dirty/PSF FITS pair directly.

  • ImagingBackend.WSCLEAN: - invert uses the WSClean dirty imaging path and returns dirty + PSF. - restore runs WSClean cleaning through the common backend interface. - Direct WSClean classes remain available for compatibility and custom commands,

    but emit a warning. Prefer get_imager(ImagingBackend.WSCLEAN).

When to use each backend

  • Use sdp for current and preferred imaging workflows.

  • Use wsclean when you want WSClean imaging through the common backend API.

  • Use rascil only for legacy compatibility or result comparison.

Migration guidance

  • Prefer passing backend explicitly in workflows and notebooks.

  • Avoid direct imports of backend-specific imagers in user-facing notebooks.

  • Keep legacy RASCIL behavior only where needed for compatibility.