The WIRCam images are correlated-sampling (CDS) images for the most part. The LowOH1 filters images are now Fowler=4 images since (since when???).

Near-IR imagers are usually shutter-less instruments which means that photons are detected immediately after the detector is RESET until it saturates. A CDS image is constructed by subtracting a REF (a read of the detector setting the start of the integration time, immediately after RESET) from the RAW (a read of the detector after the integration time) - see figure 1.

Each WIRCam detector is read in parallel using 32 amplifiers (see figure 2). Two electronic SDSU controllers are needed to read the whole 4-chip mosaic. A controller for the east chips (part #54 and #60), a second controller for the west chips (part #77 and #52). Each controller is equipped with 4 video boards with 8 amplifiers per videao boards. The numbers to keep in mind are 32 amplifiers per detector grouped in sets of 8 amplifiers per video board.

Early on, it was decided that only the CDS image be saved, the two independant reads are lost. This was to save disk space and mostly to keep things relatively simple for processing and displaying of raw images. In fact, there is no compelling reason to keep both reads as even the non-linearity correction can be effectively applied without them, with an iterative approach.