Solar Image Enhancement Based on Histogram Specification

The solar image contains a variety of different scales, different structures and different brightness active phenomena. These phenomena often causes the span of the image to be too large, resulting in hidden of faint detail structures. Furthermore, for the ground-based telescope, because of the influence of the earth atmosphere on the observations, the overall contrast of the image is decreased. These factors are not conducive for people to view the features of interest from images intuitively. To solve these problems, this paper uses the histogram specification method to deal with several targets (solar extreme ultra-violate image, sunspot, solar Hα active region and solar prominence) commonly encountered in solar observations. In this paper, the Rayleigh distribution, Double-Gaussian distribution and Triple-Rayleigh distribution is proposed to realize the contrast enhancement of these images. The effect of this method is demonstrated by the processing of solar ultraviolet images from Atmospheric Imaging Assembly on the Solar Dynamics Observatory (AIA/SDO), solar Hα image and sunspot image from New Vacuum Solar Telescope (NVST). The results show that this method can effectively improve the visibility of these solar active phenomena, and it is convenient for people to find interesting active phenomena in the early stage of the study.