Cosmic-ray Events Correction

High energy particles, i.e., cosmic-rays, often hit the surface of a detector during integration of a frame. The pixels hit by cosmic-rays have high pixel values. Such cosmic-ray events are corrected by the COSMICRAYS task. This task detects the candidate pixels which exceed mean value of the surrounding pixels within a specified detection window (either 5$\times$5 or 7$\times$7) by the amount specified by the parameter `threshold'. The COSMICRAYS task replaces the pixel value of the candidate with the average of the four neighbors.

The COSMICRAYS task can be used to remove hot or cool pixels as well as cosmic-ray events. For this purpose, the COSMICRAYS task is applied two times: it is applied to the original frames and to their inverse frames that are the original frames multiplied by $-$1, and then the inverse frames are recovered to have the signs of the original frames again. Figure 38 shows an example procedure.

  

  

  

Figure 38: An example procedure to correct cosmic ray events for an object frame.