IMSIM's image model consists of a background plus sources. The background distribution is taken from the input model dataset if present, otherwise is assumed to be flat. Sources (additional to any present in the model dataset, if used) can be added in two ways. Either a simple list of expected fluxes and positions can be supplied, or the user can specify a Log N vs. Log S relationship. In the latter case IMSIM generates a population of sources with the prescribed luminosity function and distributes them randomly in X,Y. Each psf for each source is scaled by its flux and added to the internal model.
The output images are generated by taking a total number of counts specified by the user and distributing them using the internal model.
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