An image sensor comprising: an imaging array of optically active pixels each comprising (i) a photosensitive area and (ii) a vertical CCD, VCCD, region associated therewith; proximate the imaging array, a dark-reference region of optically inactive pixels each comprising (i) a photosensitive area and (ii) a VCCD region associated therewith; a first opaque light shield (i) disposed over the dark-reference region of optically inactive pixels and (ii) defining a plurality of openings therein over the dark reference region; and a second opaque light shield (i) defining a plurality of openings therein over the dark reference region and (ii) disposed over the first light shield, wherein: within the dark-reference region, the openings in the first light shield are disposed over photosensitive areas or over VCCD regions but not over both, characterized in that, if the openings in the first light shield are disposed over photosensitive areas, then the openings in the second light shield are disposed over photosensitive areas but not over VCCD regions such that each photosensitive area in the dark-reference region has not more than one opening thereover, and if the openings in the first light shield are disposed over VCCD regions, then the openings in the second light shield are disposed over VCCD regions but not over photosensitive areas such that each VCCD region in the dark-reference region has not more than one opening thereover. an imaging array of optically active pixels each comprising (i) a photosensitive area and (ii) a vertical CCD, VCCD, region associated therewith; proximate the imaging array, a dark-reference region of optically inactive pixels each comprising (i) a photosensitive area and (ii) a VCCD region associated therewith; a first opaque light shield (i) disposed over the dark-reference region of optically inactive pixels and (ii) defining a plurality of openings therein over the dark reference region; and a second opaque light shield (i) defining a plurality of openings therein over the dark reference region and (ii) disposed over the first light shield, wherein: within the dark-reference region, the openings in the first light shield are disposed over photosensitive areas or over VCCD regions but not over both, characterized in that, if the openings in the first light shield are disposed over photosensitive areas, then the openings in the second light shield are disposed over photosensitive areas but not over VCCD regions such that each photosensitive area in the dark-reference region has not more than one opening thereover, and if the openings in the first light shield are disposed over VCCD regions, then the openings in the second light shield are disposed over VCCD regions but not over photosensitive areas such that each VCCD region in the dark-reference region has not more than one opening thereover. within the dark-reference region, the openings in the first light shield are disposed over photosensitive areas or over VCCD regions but not over both, characterized in that, if the openings in the first light shield are disposed over photosensitive areas, then the openings in the second light shield are disposed over photosensitive areas but not over VCCD regions such that each photosensitive area in the dark-reference region has not more than one opening thereover, and if the openings in the first light shield are disposed over VCCD regions, then the openings in the second light shield are disposed over VCCD regions but not over photosensitive areas such that each VCCD region in the dark-reference region has not more than one opening thereover.