Review of Image Quality Measures for Solar Imaging

• Published in: Solar physics 2017-12, Vol.292 (12), p.1-18, Article 187
• Main Authors: Popowicz, Adam, Radlak, Krystian, Bernacki, Krzysztof, Orlov, Valeri
• Format: Article
• Language: English
• Subjects: Astrophysics and Astroparticles; Atmospheric models; Atmospheric Sciences; Computer simulation; Data imaging; Discrete cosine transform; Frames; Granulation; Identification methods; Image quality; Image reconstruction; Parameter identification; Photosphere; Physics; Physics and Astronomy; Post-production processing; Quality; Quality assessment; Random waves; Routines; Satellite imagery; Solar imagery; Solar observations; Solar optical telescope; Solar physics; Solar system; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Turbulence
• ISSN: 0038-0938; 1573-093X
• DOI: 10.1007/s11207-017-1211-3

Observations of the solar photosphere from the ground encounter significant problems caused by Earth’s turbulent atmosphere. Before image reconstruction techniques can be applied, the frames obtained in the most favorable atmospheric conditions (the so-called lucky frames) have to be carefully selected. However, estimating the quality of images containing complex photospheric structures is not a trivial task, and the standard routines applied in nighttime lucky imaging observations are not applicable. In this paper we evaluate 36 methods dedicated to the assessment of image quality, which were presented in the literature over the past 40 years. We compare their effectiveness on simulated solar observations of both active regions and granulation patches, using reference data obtained by the Solar Optical Telescope on the Hinode satellite. To create images that are affected by a known degree of atmospheric degradation, we employed the random wave vector method, which faithfully models all the seeing characteristics. The results provide useful information about the method performances, depending on the average seeing conditions expressed by the ratio of the telescope’s aperture to the Fried parameter, D / r 0 . The comparison identifies three methods for consideration by observers: Helmli and Scherer’s mean, the median filter gradient similarity, and the discrete cosine transform energy ratio. While the first method requires less computational effort and can be used effectively in virtually any atmospheric conditions, the second method shows its superiority at good seeing ( D / r 0 < 4 ). The third method should mainly be considered for the post-processing of strongly blurred images.