Sky and Telescope - July 2017 - 68
by Ron Brecher
Recover information in your deep-sky
images with this powerful technique.
Most of us don't have the luxury of imaging with an orbiting space telescope, where there's no atmosphere to degrade
our images. For us Earth-based imagers, the reality is that
turbulent air inevitably blurs detail in our deep-sky shots.
Even in the steadiest seeing conditions, the "true" image -
as it would be with no degradation - is convolved, or mixed,
with the blurring effect of the atmosphere and distortions
caused by imperfect optics. Fortunately, many image-processing software packages include powerful deconvolution and
sharpening tools that can recover much of the detail buried
in your frames.
Sharpening and deconvolution tools work in very different
ways. Sharpening primarily increases contrast along welldeﬁned edges in images, whereas deconvolution performs an
iterative pixel-by-pixel restoration using a mathematical model
of the blurring function, leading to an overall sharper image.
Deconvolution is rooted mainly in work done by Norbert
Wiener of MIT. He published these ﬁndings in the 1949 book
Extrapolation, Interpolation and Smoothing Stationary Time Series
with Engineering Applications. Since then, deconvolution has
been used in weather forecasting, seismology, spectroscopy,
microscopy, forensic photography, and many other scientiﬁc
and engineering applications, including, of course, astronomy.
In one famous example, deconvolution was used to improve
early Hubble Space Telescope images impaired due to the orbiting observatory's ﬂawed primary mirror (S&T: Oct. 1990, p.
352). In the nearly 70 years since its development, deconvolution has become an essential image-processing step for most
professional and many amateur astrophotographers.
t NOTABLE DIFFERENCE Deconvolution can restore faint stars and
small-scale detail hidden by the blurring effects of our atmosphere. This
pair of images show a close-up of Herbig-Haro Object 555 (circled) in
the Pelican Nebula. The bottom image uses Regularized RichardsonLucy deconvolution in PixInsight to tighten up many stars, as well as
features within the nebula itself.
J U L Y 2 0 1 7 * SK Y & TELESCOPE
ALL IMAGES COURTESY OF THE AU THOR
Sharpening vs. Deconvolution