Selecting Field of View (FOV) Camera guidance
Johnson’s Criteria charts Thermal imaging cameras are specified with a Field of View (FOV) or a Focal Length and most cameras have a fixed focus non-zoom lens. Although dual FOV cameras are available in the HT07 and Osiris ranges below, but add to the cost.
The detection zones of a thermal imaging camera are often specified using the Johnson Criteria Charts, which allow the detection, recognition and identification ranges to be compared between thermal cores.
The minimum required resolution according to Johnson’s criteria are expressed in terms of line pairs of image resolution across a target, in terms of several tasks.
Detection, an object is present (1,0 +/-0.25 line pairs)
Recognition the type of object can be discerned, a person versus a car (4 +/- 0.8 line pairs)
Identification, a specific object can be discerned, a woman versus a man, the specific car (6.4+/- 1.5 line pairs)
These amounts of resolution give a 50% probability of an observer discriminating an object to the specified level.
Additionally, the line pairs refer to lines being displayed on an interlaced CRT monitor. Each line pair corresponds to 2 pixels of a film image, or image displayed on LCD monitor.