... 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. ... By uniform weighting, we mean that the weight is a constant for all pixels in an input image. ...