astroscrappy Package

Astro-SCRAPPY: The Speedy Cosmic Ray Annihilation Package in Python

An optimized cosmic ray detector

Author:Curtis McCully

Astro-SCRAPPY is designed to detect cosmic rays in images (numpy arrays), originally based on Pieter van Dokkum’s L.A.Cosmic algorithm.

Much of this was originally adapted from written by Malte Tewes. I have ported all of the slow functions to Cython/C, and optimized where I can. This is designed to be as fast as possible so some of the readability has been sacrificed, specifically in the C code.

L.A.Cosmic = LAplacian Cosmic ray detection

If you use this code, please consider adding this repository address in a footnote:

Please cite the original paper which can be found at:

van Dokkum 2001, PASP, 113, 789, 1420 (article :

This code requires Cython, preferably version >= 0.21.

Parallelization is achieved using OpenMP. This code should compile (although the Cython files may have issues) using a compiler that does not support OMP, e.g. clang.


There are some differences from original LACosmic:

  • Automatic recognition of saturated stars. This avoids treating such stars as large cosmic rays.
  • I have tried to optimize all of the code as much as possible while maintaining the integrity of the algorithm. One of the key speedups is to use a separable median filter instead of the true median filter. While these are not identical, they produce comparable results and the separable version is much faster.
  • This implementation is much faster than the Python by as much as a factor of 28 depending on the given parameters. This implementation is much faster than the original IRAF version, by a factor of ~90.

Note that arrays always must be C-contiguous, thus all loops are y outer, x inner. This follows the Pyfits convention.

scipy is required for certain tests to pass, but the code itself does not depend on scipy.


detect_cosmics(indat[, inmask, sigclip, …]) Detect cosmic rays in a numpy array.