With the current implementation of pixel level simulation and extraction, output fluxes are biased because of a correlation between inverse variance (ivar) and fluxes in CCD images due to Poisson noise.
new field in image datamodel ?
One way to fix this is to weight pixels according to readout noise only, but this means tracking the readout noise scaled by the pixel level flat field along with the inverse variance. This would be a change in the data model of images (we cannot drop totally the ivar field because we still need it for chi2 evaluation).
evaluate loss of optimality
Some work is needed to evaluate if we can afford or not the loss of optimality with this simple readout noise weighting. It would be interesting to run 2 extractions of the same simulated images to test this even if a analytical formula exists.
This issue is also posted in desispec because of the data format issue.
With the current implementation of pixel level simulation and extraction, output fluxes are biased because of a correlation between inverse variance (ivar) and fluxes in CCD images due to Poisson noise.
This issue is also posted in desispec because of the data format issue.