Review for DM-5161: Support a full background model when detecting cosmic rays

[jdswinbank]

No description provided.

[jdswinbank]

I see the logic here, but: what happens if we call estimateBackground even when nx*ny is less than 1?

• If it uses the median, can we just call it here? It simplifies the logic since we don't need to handle this case specially.
• If it doesn't just use the median, what's the justification for using the same technique here as in estimateBackground for small bins, and a different technique for large bins?

[laurenam]

The way I see it, the current logic is much simpler for the nx*ny<=1 case. This is because the estimateBackground function returns an exposure and a lsst.afw.math.mathLib.Background object (computed based on the config values, for which the default is indeed set to MEDIAN here). The variable bg fed into findCosmicRays is a double, so I would still need to compute that with afwMath.makeStatistics(bg.getImageF(), afwMath.MEDIAN).getValue() after having run bg, exposure = measAlg.estimateBackground(exposure, self.config.cosmicray.background, subtract=False) and note that I have set subtract=False in the above as we do not actually want a background subtracted copy of the image here (although I suppose we could do that as in the nx*ny>1 case, but that seems like an extra operation that is not required for the majority of cases).

I can confirm that the MEDIAN sky level is the same for the case I gave above as it is in the current implementation.

In all, I am inclined to leave the current logic.