  Aims: To formulate, implement, and validate a user-independent release of
CLEAN for Fourier-based image reconstruction of hard X-rays flaring sources.
Methods: CLEAN is an iterative deconvolution method for radio and hard X-ray
solar imaging. In a specific step of its pipeline, CLEAN requires the
convolution between an idealized version of the instrumental Point Spread
Function (PSF), and a map collecting point sources located at positions on the
solar disk from where most of the flaring radiation is emitted. This
convolution step has highly heuristic motivations and the shape of the
idealized PSF, which depends on the user's choice, impacts the shape of the
overall reconstruction. Here we propose the use of an
interpolation/extrapolation process to avoid this user-dependent step, and to
realize a completely unbiased version of CLEAN. Results: Applications to
observations recorded by the Spectrometer/Telescope for Imaging X-rays (STIX)
on-board Solar Orbiter show that this unbiased release of CLEAN outperforms the
standard version of the algorithm in terms of both automation and
reconstruction reliability, with reconstructions whose accuracy is in line with
the one offered by other imaging methods developed in the STIX framework.
Conclusions: This unbiased version of CLEAN proposes a feasible solution to a
well-known open issue concerning CLEAN, i.e., its low degree of automation.
Further, this study provided the first application of an
interpolation/extrapolation approach to image reconstruction from STIX
experimental visibilities.
