A python package for over-sampled image construction, difference-imaging, transient detection, and difference-image PSF photometry for the Nancy Grace Roman Space Telescope.

The algorithms are described in the accompanying paper.

Albrow, M.D., 2025, AJ, 169, 297

The tests directory contains sample scripts for running the package. Typically they would be run in the order:

python test_difference_images.py config_paper_split.json

python test_detect.py config_paper_split.json

python test_photometry.py config_paper_split.json

The config file, and the scripts, should be edited for your specific purpose.

A sample json configuration file looks like:

{
  "data_dir": "/home/users/mda45/RomanISIM/Data/paper",
  "data_root": "dazzle_paper_t",
  "output_dir": "/home/users/mda45/RomanISIM/Data/paper_results",
  "input_xrange": [
    0,
    4088
  ],
  "input_yrange": [
    0,
    4088
  ],
  "image_splits": 4,
  "difference_image_iterations": 5
}

Most of this is self explanatory. Setting image_splits = 4 means that the 4088 x 4088 images are split into 16 x (1022 x 1022) size, processed in parallel, and with the output sent to different directories.

Simulated images used in the paper are available at http://www2.phys.canterbury.ac.nz/data/RomanISIM/