False colour image
A colour image where parts of the non-visible EM spectrum are expressed as one or more of the red, green, and blue components, so that the colours produced by the Earth's surface do not correspond to normal visual experience. Also called a false-colour composite (FCC). The most commonly seen false-colour images display the very-near infrared as red, red as green, and green as blue.

False color photograph
Another term for IR color photograph.

Far range
The portion of a radar image farthest from the aircraft or spacecraft flight path.

Film
Light-sensitive photographic emulsion and its base.

Film speed
Measure of the sensitivity of photographic film to light. Larger numbers indicate higher sensitivity.

Filter, digital
Mathematical procedure for modifying values of numerical data.

Filter, optical
A material that, by absorption or reflection, selectivity modifies the radiation transmitted through
an optical system.

Flight path
Line on the ground directly beneath a remote sensing aircraft or space craft. Also called flight line.

Fluorescence
Emission of light from a substance following exposure to radiation from an external source.
FMC Forward Movement Compensation. Mechanism that drives the film of a photogrammetric camera in the opposite direction and same apparent speed generated by the aircraft’s forward motion.

F-number
Representation of the speed of a lens determined by the focal length divided by diameter of the lens. Smaller numbers indicate faster lenses.

Focal length
In cameras, the distance from the optical center of the lens to the plane at which the image of a very distant object is brought into focus.

Foreshortening
A distortion in radar images causing the lengths of slopes facing the antenna to appear shorter on the image than on the ground. It is produced when radar wavefronts are steeper than the topographic slope.

Format
Size of an image.

Forward overlap
The percent of duplication by successive photographs along a flight line.

Fovea
The region around that point on the retina intersected by the eye's optic axis, where receptors are most densely packed. It is the most sensitive part of the retina.

Frequency (v )
The number of wave oscillations per unit time or the number of wavelengths that pass a point per unit time.

F-stop
Focal length of a lens divided by the diameter of the len's adjustable diaphragm. Smaller numbers indicate larger openings, which admit more light to the film.