The Johnson Criteria assumes that the critical dimension for a human being is 0.75 meters. To get DRI, you need 1.5 pixels, 6 pixels and 12 pixels across 0.75 meters in the object pane.
That means:
- Detection
1.5 pixels / 0.75m = 2 pixels per meter
- Recognition
6 pixels / 0.75m = 8 pixels per meter
- Identification
12 pixels / 0.75m = 16 pixels per meter
Assuming that a man is 1.83m by 0.5m, the following would apply:
Detection
3.6 pixels by 1 pixel
(You can see
something is there)
Recognition
13 pixels by 5 pixels
(You can see that a person
is there)
Identification
28.8 pixels by 8 pixels
(You can see that the
person looks like a civil man)
Assuming that a vehicle is 4m by 1.5m, the following would apply:
Detection
2.8 pixels by 1 pixel
(You can see something
is there)
Recognition
13 pixels by 5 pixels
(You can see that a
vehicle is there)
Identification
26 pixels by 10 pixels
(You can see that the vehicle
may be a off-road vehicle)
