Electro-Optical/Infrared (EO/IR) Theory and Systems
https://spp.fas.org/military/program/track/eo-ir.pdf The instantaneous field of view (IFOV) is a fundamental sensor parameter. At range
R, a single IFOV covers a distance D = IFOV*R. As an example, detectors for visible
digital cameras (Nikon, Canon) are about 10 μm in size. With a 100-mm lens the IFOV =
(10*10-6)/(100*10-3) = 10-4. At a range of 1 ,000 meters, the IFOV covers 10 cm. If the
target were 1 meter x 1 meter, we might say there were 10 x 10 = 100 IFOVs on target;
this is usually replaced with the sloppier phrase, 100 pixels on target
The choice of optics and detector affect the magnification provided an d image
clarity. Image quality includes measures of:
• Contrast – Degree of difference between lightest and darkest portions of image
• Luminance – Brightness of image
• Noise – Random signal from sources outside the image itself
• Sampling – Digitization due to binning of signal into pixels
• Blur – Smearing of image due to diffraction and/or imperfect focus (e.g., due to
jitter)
• How many pixels are required to give a 50% probability of an observer discriminating
an object to a specified level?
• Experiments with observers yielded the following
− Detect (determine if an object is present) 1.5 pixels
− Recognize (see what type of object it is; e.g., person, car, truck) 6 pixels
− Identify (determine if object is a threat) 12 pixels
• These are the number of pixels that must subtend the critical dimension of the object,
determined by statistical analysis of the observations
− Critical dimension of human 0.75 m
− Critical dimension of vehicle 2.3 m
• Hence for a human, the requirements are
− Detect 2 pixels/meter
− Recognize 8 pixels/meter
− Identify 16 pixels/meter
• For a man who is 1.8 m x 0.5 m, this corresponds to requirements of
− Detect 3.6 pixels tall by 1 pixel wide
− Recognize 14.4 pixels tall by 4 pixels wide
− Identify 28.8 pixels tall by 8 pixels wide
Johnson Criteria