Hot pixels or cosmics lying in the footprint are flagged using the Laplacian detection method published in van Dokkum (2001). The algorithm is based on the measurement of the seeing and the noise level of the image background to select cosmic-rays of arbitrary shapes by the sharpness of their edges.

The efficiency of the algorithm has been tested by measuring the number of cosmics in a dark image and a stellar field, then on the sum of both images. The ratio of the number of detections in both case being an assessment of its performance. The result is about 99% of common detections. In the 800 by 60 pixels rectangles of the footprints, the total number of flagged pixels is typically between 0 and 5.