The STIPS PSF Grid

Overview

Starting with STIPS 2.0.0, STIPS uses WebbPSF PSF grids to implement an ePSF. The ePSF uses a 3x3 grid of PSFs to handle PSF variation across the detector, and an oversample of 4x4 to handle sub-pixel positioning. Each point source has its PSF calculated individually as it is added to the detector.

Internal Image Size

The size of the STIPS pre-convolution image is set by the size of the detector. In addition, the image is padded by half of the PSF size on each side in order to include sources that fall off the detector, but whose PSF may land on the detector.

PSF Image Size

The size of the STIPS generated PSF image depends on the source brightness. For most sources, a 45x45-pixel PSF is created via an ePSF oversampled to a factor of 4. For bright sources (magnitude < the bright limit, default 14), a 91x91-pixel PSF is created to provide flux from the extended wings. For extra-bright sources (magnitude < the extra-bright limit, default 3), a 181x181-pixel PSF is created to provide even more wing flux to the model.