Project: datamanagement
Issue DM-4366: Improve overscan correction for DECam raw data
Currently, the default overscan correction from IsrTask is used for processing DECam raw data. Overscan subtraction is done one amplifier at a time. However, a bias jump occurs due to the simultaneous readout of the smaller ancillary CCDs on DECam, some images show discontinuity in the y direction across one amplifier, as in the example screen shot. This ticket is to improve overscan correction for DECam data so to mitigate this discontinuity in the ISR processing. Arrangement of CCDs on DECam: http://www.ctio.noao.edu/noao/sites/default/files/DECam/DECamPixelOrientation.png h3. More details: There are 6 backplanes in the readout system, shown by the colors in DECamPixelOrientation.png. In raw data files, the CCD's backplane is noted in the header keyword "FPA". Examination of some images suggests that science CCDs on orange and yellow backplanes show bias jump at 2098 pixels from the y readout. That is the y size of the focus CCDs. h3. Actions: For CCDs on the affected backplanes, divide the array into two pieces at the jump location, and do overscan correction on the upper and lower pieces separately.
Story points: 5