DRI ranges enable one to easily estimate the maximum range that an object can be either detected, recognized or identified. It is important to note that these estimates are based solely on geometrical parameters – the target size, distance, lens focal length and camera detector pixel size. Signal level, detector sensitivity, atmospheric conditions and other factors are not considered!
The calculations used here are based on the “Johnson Criteria”. According to the Johnson Criteria, the minimum resolution, pixels on target, required to achieve a 50% probability for an observer to discriminate an object are:
- Detection: An object is present – 2 pixels on target (Lower Bar)
- Recognition: discern the type of object, a human vs. a vehicle – 8 pixels on target (Middle Bar)
- Identification: discern specific objects, a man vs. a woman, a car model – 12.8 pixels on target (Upper Bar)