Summary of CR Treatment

The correction factor computed from each image is set to zero at the positions of CR hits. The contribution to the correction factor which is then missing due to those zeros, , is filled with contributions from all images, where each image contributes proportional to its local weight. If for example the PSF is undersampled, a hole in image 1 will closely resemble an otherwise flat image that is zero at the affected pixels. In that case, the missing contribution, , will be filled only by the other images which are not affected. On the other hand, for a well sampled PSF, only little information is locally lost, but many pixels are affected. Therefore, the weight of the not affected images is only slightly increased relative to the affected images, but over a large number of pixels. In other words, CR hits do not only destroy information about the flux at the position of the hit, but also some information for neighboring pixels within the PSFs. This is accurately taken care of by this procedure.