Design And Implementation Of Denoising And Star-Searching In CCD Astronomical Images

Astronomical CCD (Charge-Coupled Device) images are normally affected by kinds of noises during acquisition and transmission. It is necessary to research how to reduce the noises effectively and to realize the star searching and its centering. In this paper, a ROAD (Rank-Ordered Absolute Difference) algorithm to remove impulse noises and stellar-searching in CCD image are systematically introduced.Due to the interference of cosmic rays, some "salt noises" can systematically introduce into CCD images during their acquisition. The ROAD statistical values quantify how different in intensity the particular pixels are from their most similar neighbors. The noise removal filter based on a simple statistic to detect impulse pixels is to effectiVely remove noise from an image while keeping its features intact. The marginal distribution of a stellar image is a Gaussian on the whole, which is used to design the stellar searching algorithm, and some limits must be set to improve the function of the algorithm. A method called a 2D modified moment is chosen to calculate the center of a stellar image. With its initial center and background from its stellar searching, an accurate center and photometry of a star can be calculated.The implementation of the design with Visual C++ .Net 2003 is also described in the thesis. Many CCD images are used to test the mentioned-above algorithms. The results after compared with former ones show the feasibility and effectiveness of these algorithms.