New method of enhancement using wavelet transforms applied to SODISM telescope

Abstract

Ipson, Stanley S.; Hauchecorne, A.; Meftah, M Citation Alasta AF, Algamudi A, Qahwaji R, Ipson S, Hauchecorne A and Meftah M (2018) New method of Enhancement using Wavelet Transforms applied to SODISM Telescope. Advances in Space Research. 63(1): 606-616. Rights  Abstract: PICARD is a space-based observatory hosting the Solar Diameter Imager and Surface Mapper (SODISM) telescope, which has continuously observed the Sun from July 2010 and up to March 2014. In order to study the fine structure of the solar surface, it is helpful to apply techniques that enhance the images so as to improve the visibility of solar features such as sunspots or faculae. The objective of this work is to develop an innovative technique to enhance the quality of the SODISM images in the five wavelengths monitored by the telescope at 215.0 nm, 393.37 nm, 535.7 nm, 607.1 nm and 782.2 nm. An enhancement technique using interpolation of the high-frequency sub-bands obtained by Discrete Wavelet Transforms (DWT) and the input image is applied to the SODISM images. The input images are decomposed by the DWT as well as Stationary Wavelet Transform (SWT) into four separate sub-bands in horizontal and vertical directions namely, low-low (LL), low-high (LH), high-low (HL) and high-high (HH) frequencies. The DWT high frequency sub-bands are interpolated by a factor 2. The estimated high frequency sub-bands (edges) are enhanced by introducing an intermediate stage using a stationary Wavelet Transform (SWT), and then all these sub-bands and input image are combined and interpolated with half of the interpolation factor α/2, used to interpolate the high-frequency sub-bands, in order to reach the required size for IDWT processing. Quantitative and visual results show the superiority of the proposed technique over a bicubic image resolution enhancement technique. In addition, filling factors for sunspots are calculated from SODISM images and results are presented in this work.

Filling Factors of Sunspots in SODISM Images

“…The biggest advantage is the reduction in time consumption. There are only a few methods applied to segmented SODISM images; the first was applied by Meftah et al [11] to 393nm W.L. but needed manual interaction to optimize the threshold, which was calculated using the Otsu method [7].…”

“…but needed manual interaction to optimize the threshold, which was calculated using the Otsu method [7]. The second method developed by Ahmed et al shows a strong correlation coefficient of 98% [11] between the SODISM and SOHO images. This was only slightly less than that achieved in the same period in the third method by Alasta et al, which successfully detected sunspots on 535nm W.L.…”

“…Ashamari et al introduced internal work2 [11], which is a method for detecting sunspots from SODISM images (at a 535nm band). They first applied a Wavelet Harr filter to remove noise from the image and then used a band-pass filter to remove limb darkening.…”