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		| Paper: | 
		Robust Estimation and Image Combining | 
	 
	
		| Volume: | 
		77, Astronomical Data Analysis Software and Systems IV | 
	 
	
		| Page: | 
		514 | 
	 
	
		| Authors: | 
		Zhang, C. Y. | 
	 
	
	
		| Abstract: | 
		A task GCOMBINE in the STSDAS package, for combining images, is briefly reviewed. With a stack of input images, one can identify bad pixels by comparing the deviation of a pixel from the mean with a user-specified threshold times the clipping sigma. It is crucial that estimation of the mean and sigma be robust against unidentified outliers, in order to reject cosmic ray events effectively. A variety of weighting schemes and means for storing noise characteristics are discussed. Information in neighboring pixels can also be used in a global way to identify cosmic rays. | 
	 
	
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