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Registration and stacking

For templates that do not use chopping, please refer to the description given for SW data as the technique is the same.

For templates that use chopping, one registers the positive images. Since there are many hot pixels, it is very helpful if there are several images to register and if these images are offset from one another.

The final step is optional and depends on how crowded the field is. One can use the two negative images that are either side of the positive image to increase the S/N ratio of the central image. The end result will be a central positive image with an exposure scaling of 4*DIT seconds, two negative images with an exposure scaling of 3*DIT seconds and two additional positive images with an exposure scaling of DIT seconds. This step should not be applied to images for which the non-linearity correction was done on the chopped frames, unless the negative beams have been treated correctly.

Christopher Lidman