Mr. Ali Khalil Benkhalil Profile

Ali Khalil Benkhalil

at Univ of Bradford

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Proceedings Article | 11 February 2003 Paper

Automated image standardization of the synoptic solar observations at the Meudon observatory

Stan Ipson, Valentin Zharkova, Ali Benkhalil, S. Zharkov, Jean Aboudarham

Proceedings Volume 4853, (2003) https://doi.org/10.1117/12.479499

KEYWORDS: Observatories, Image analysis, Distortion, Calcium, Image processing, Image segmentation, Sun, Image filtering, Algorithm development, Edge detection

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The robust techniques developed to put the synoptic solar images into a standardized form of a 'virtual solar image' are presented. The techniques include limb fitting, removal of geometrical distortion, centre position and size standardization and intensity normalization. The limb fitting starts with an initial estimate of the solar centre using raw 12-bit image data and then applies a Canny edge-detection routine. Candidate edge points for the limb are selected using a voting method and the chosen points fitted to a quadratic function by minimizing the algebraic distance using SVD. The five parameters of the ellipse fitting the limb are extracted from the quadratic function. Together with knowledge of cause of the geometrical distortion these parameters are used to define an affine transformation that corrects the image shape. Corrected images are generated using the nearest neighbor, bilinear or bicubic interpolation. Intensity renormalization is also required because of a limb darkening and variation in the atmosphere visibility over the solar disc. It is achieved by fitting a background function in polar co-ordinates to a set of sample points having the median intensities and by standardizing the average brightness. Representative examples of intermediate and final processed results are presented in addition to the algorithms developed. The techniques were also applied to the some images taken from BBSO, Kanzelhoehe and Kiepenheuer Institution observatories. The research is done for the European Grid of Solar Observations (EGSO) project, IST-2001-32409.

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