Left: single raw VIS bias frame captured at L2. The image exhibits numerous CRs, and has been corrected with a fixed pedestal level per quadrant based on the median value in the overscan area. Right: correction using a smoothed vertical vector of the overscan area. The contrast here is maximised to highlight effects at the sub-ADU level. The solution adopted on the right still exhibits an instrumental signature (some quadrants, or entire detectors, have a non-zero signal), necessitating an additional two-dimensional bias correction.