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  1. Data Management
  2. DM-4232

Variance is set after dark subtraction

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    • Story
    • Status: Done
    • Resolution: Done
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    • ip_isr
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    Description

      In the default IsrTask, the variance is currently set after dark subtraction. This means that photon noise from the dark is not included in the variance plane, which is incorrect. The variance should be set after bias subtraction and before dark subtraction.

      hchiang2 also points out (DM-4191) that the AssembleCcdTask with default parameters requires amplifier images with variance planes, even though the variance cannot be set properly until after full-frame bias subtraction. I believe that AssembleCcdTask only requires a variance plane in the amp images because it does an "effective gain" calculation, but I suggest that this isn't very useful (an approximation of an approximation, and you're never going to use that information anyway because it's embedded in the variance plane with better fidelity). I therefore suggest that this effective gain calculation be stripped out and that AssembleCcdTask not require variance planes.

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            krughoff Simon Krughoff (Inactive) added a comment - - edited

            O.K. ci_hsc and validate_drp both passed, but validate_drp only took 18 sec. Should I be worried?

            Edit: Sorry I was confused. validate_drp and ci_hsc are not executed in the same way. validate_drp is currently down, but should be back up soon.

            krughoff Simon Krughoff (Inactive) added a comment - - edited O.K. ci_hsc and validate_drp both passed, but validate_drp only took 18 sec. Should I be worried? Edit: Sorry I was confused. validate_drp and ci_hsc are not executed in the same way. validate_drp is currently down, but should be back up soon.
            rowen Russell Owen added a comment - - edited

            validate_drp doesn't do much when you build it. You have to run it to see what happens. I suggest you run the demo for CFHT using the code before your changes and after to see what changes (if anything). You could run the DECam demo as well, but I suspect it does not run ISR.

            rowen Russell Owen added a comment - - edited validate_drp doesn't do much when you build it. You have to run it to see what happens. I suggest you run the demo for CFHT using the code before your changes and after to see what changes (if anything). You could run the DECam demo as well, but I suspect it does not run ISR.

            O.K. so I can't run validate_drp against a ticket branch, but ci_hsc passes, so I think that means my changes are o.k.

            If I don't hear a lot of shouting from price I'm going to merge this week.

            krughoff Simon Krughoff (Inactive) added a comment - O.K. so I can't run validate_drp against a ticket branch, but ci_hsc passes, so I think that means my changes are o.k. If I don't hear a lot of shouting from price I'm going to merge this week.
            price Paul Price added a comment -

            The changes to obs_subaru look fine, thanks. Just a couple of comments on the GitHub PR to clean things up.

            price Paul Price added a comment - The changes to obs_subaru look fine, thanks. Just a couple of comments on the GitHub PR to clean things up.

            People

              krughoff Simon Krughoff (Inactive)
              price Paul Price
              Hsin-Fang Chiang
              Hsin-Fang Chiang, Lauren MacArthur, Meredith Rawls, Paul Price, Robert Lupton, Russell Owen, Simon Krughoff (Inactive)
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