Change to finding similar stars method.
Change to finding similar stars method.

The existing behavior finds the overall observational sum of the
sum of squared differences (SSD) of each frame. This leads to a singular
value where small numbers indicate "similarity".

This changes first finds the SSD of each stamp (frame), then constructs a weight
based on the signal to noise ratio for that stamp to the overall SNR for
the observation.

panoptes/PIAA