Fill factor (image sensor)

The fill factor of an image sensor array is the ratio of a pixel's light sensitive area to its total area. For pixels without microlenses, the fill factor is the ratio of photodiode area to total pixel area,[1] but the use of microlenses increases the effective fill factor, often to nearly 100%, by converging light from the whole pixel area into the photodiode.[2]

Another case that reduces the fill factor of an image is, to add additional memory beside each pixel, to achieve global shutter effect on CMOS sensor.[3]

Additional memory to achieve global shutter effect for CMOS sensor[3].