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Realigning after new lights are obtained

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  • Robert
    Q: If I have it right, when lights are aligned, they are resampled, so a little of good data is lost. In MaximDL, for example, one can sift through lights
    Message 1 of 2 , Feb 3, 2012
      Q:
      If I have it right, when lights are aligned, they are resampled, so a little of good data is lost.
      In MaximDL, for example, one can sift through lights based on criteria, and save the good ones to a new folder, after alignmet.
      If later later collect new lights, sift, and add to the same folder, and then process that good group, that would be a convenient workflow, but is it a bad practice, or is the dataloss insignificant (pretty pictures, not photometry).
      TIA for your thoughts.
      Bob Hertel
    • Stan
      ... That s a somewhat complicated topic that hinges on sampling (pixel size as a function of fwhm), number of frames, and method of resampling. But essentially
      Message 2 of 2 , Feb 3, 2012
        --- "Robert" <robert.hertel@...> wrote:
        > If I have it right, when lights are aligned,
        > they are resampled, so a little of good data is lost.

        That's a somewhat complicated topic that hinges on sampling (pixel size as a function of fwhm), number of frames, and method of resampling.

        But essentially you will always have to resample all but 1 frame as a part of the registration process. If you try to avoid registration by not offsetting (dithering) the sub-exps then you are asking for much more trouble in regards to persistent noise and outliers; and even if you do not deliberately dither, it is difficult to avoid field rotation and drift, so you should still register/resample.

        Maybe you are asking about double-registration? (e.g. register frames from night 1 then register night 2 frames to a different master, then have to register master 1 to master 2). Double registration should generally be avoided and it is easy to avoid. If you have several nights of sub-exp then simply process all frames for all nights at the end of the total run. Or use the combined image from night 1 as the registration master for night(s) 2+. Generally it is best to create a master from all sub-exps rather than create a master from sub-masters unless you really know what you are doing visa-vie weighting the master combine.

        Stan
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