Execution starts with the processing of the dome flat.
Then the task mkskycor creates a smoothed version of the image, retaining only the large-scale variations in the dome flat. The dome residual is multiplied by the smoothed skyflat and the resulting image normalized to yield the superflat. Finally, any values below 0.1 in the superflat are replaced by unity to avoid creating noisy regions at the corners of flatfielded images. You may need to revise the ccdproc parameters after running this task.