Controlling Dynamic Range
Compared to film, digital sensors are much more sensitive to light. This sensitivity can lead to problems when there is a wide tonal variation in the scene—in these contrasting instances it’s often difficult for the sensor to record detail in the highlight areas.
The larger the photodiode, the greater the sensitivity and the wider the dynamic range, but this is in conflict with the need for smaller photosites on the sensor to increase the resolution. The photodiode must fit within the total photosite area, and still leave sufficient room for other components. Moreover, typical photodiodes still reach saturation (that is, a full tonal range) faster than is ideal.
In highlight areas, digital sensors ...