Schematic view of the photo-sensitive area of the CCD. The 200 × 200 square inside the 1024 × 1024 full CCD is the region of interest, called subarray, transmitted to ground. Margins in the left: 4 prescan columns, 8 blank columns (unused), and 16 + 16 dark columns. Margins in the top: 6 overscan rows, 3 dark rows. The bottom storage section, not represented, mirrors the CCD, including margins. The arrows on the top and right of the diagram represent the x- and y-axis of the pixels of the full CCD, respectively.