Scope of Level 1 Single-Frame Processing

I’m trying to work out the differences between Single-Frame Processing in Level 1 and Level 2. Given that the DPDD only shows DIASource and image outputs for Level 1, I think that means the Level 1 Single Frame Processing is limited to just ISR and Image Characterization, or more precisely:

  • ISR
  • Defect / CR repair
  • Detection of bright stars
  • Basic PSF estimation
  • Basic measurement
  • Single-frame astrometric calibration
  • Single-frame photometric calibration
  • Background estimation
    Where “basic” essentially means “only what’s necessary to do astrometric/photometric calibration”.

The Level 2 version needs to include all of the above, using slower but more careful algorithms for most of them, as well as:

  • Detection to the single-epoch 5-sigma limit
  • Full single-epoch meblending
  • Full single-epoch measurement

In the parlance of our current Tasks, that pretty much means Level 1 is just CalibrateTask and IsrTask, while Level 2 is the full content of ProcessCcdTask. Does that match everyone else’s understanding?

I think it’s correct that calibrated science image detection, deblending, and measurement do not need to be done in Level 1; these are only done on the difference image. I’m not sure that PSF estimation can be just “basic” because we’ve promised it as a quality parameter; it kind of depends what the difference between “basic” and “more careful” is. But basically correct, according to my understanding and reading of the DPDD.