What are reasonable dither strategies for cosmic rays, warm pixels, undersampling?
There is no single observing strategy that is entirely satisfactory in all circumstances for WFPC2. One must consider cosmic rays, warm pixels (i.e. pixels with high and time variable dark count), spatial undersampling of the image, and trading signal-to-noise for ability to recognize and deal with these features. The optimal strategy chosen depends crucially on the scientific question: is the underlying structure totally unknown, is spatial resolution of paramount importance, is photometric accuracy the most crucial aspect, etc.? 1) Cosmic Rays: The best way to deal with cosmic rays is to CR-SPLIT the exposures (take multiple exposures at a FIXED image location). Note that even with two exposures taken at a fixed position there will be some cosmic rays that overlap. As an example, for an observer that has two 2000s exposures, about 1000 pixels per chip will be unrecoverable because they have been hit in both images. Furthermore, because CR events typically affect ~7 pixels per event,
