read rate: The percentage representing the number of successful reads per 100
attempts to read a particular symbol. An attempt is a single pass of the scanner,
or a single trigger pull, depending upon the application.
reader: A device used to capture the data encoded in a machine-readable
symbol or other automatic data capture media. Machine-readable symbol
readers consist of two parts: the transducer that sends signals proportional to
the reflectivity of each successive element of the symbol to the decoder, that
examines the signals from the scanner and translates them into recognizable or
computer-compatible data. The decoder itself is sometimes called a reader.
redundancy: Characteristic whereby information is repeated to increase the
probability of its being read or communicated successfully. In a bar code symbol
the height of the bars provides vertical redundancy by enabling multiple scan
paths to exist through the symbol, only one of which is necessary in theory for a
complete decode.
reference decode algorithm: The decode algorithm quoted in a symbology
specification as the basis for the derivation of tolerances, decodability values,
and the like.
reference threshold: In a decode algorithm, a reference point at which a
decision is made to select between two possible values.
reflectance: (1) The amount of light of a specified wavelength or range of
wavelengths that is reflected from a surface. (2) (sometimes called “reflectance
factor”). Reflectance is measured on a scale of 0 to 1, at a wavelength or
bandwidth of light (spectral response) specified in the particular application
specification. Reflectance = R/I where R = Reflected light, I = Incident light
Barium sulfate or magnesium oxide are used as 'near perfect' reference white
standards (a perfect standard of pure white would have a reflectance of 1.00 at
any wavelength of light). The absence of any light in a vacuum is used as
reference black standard. Samples (such as substrates, inks, and the like) are
tested against the standards under similar illumination.
reflectance (absolute): The ratio of the total reflectance by a substrate to the
total light incident on that substrate.
reflectance (difference): The difference between the reflectances of light and
dark elements of a machine-readable symbol.
reflectance (diffuse): Reflected light whose angle of reflection varies from the
angle of incidence of the illuminating light, such as in reflection from a rough
surface.
reflectance (factor): The ratio of reflected flux to the reference reflected flux.
reflectance (specular): Reflected light whose angle of reflection is equal, or
nearly equal, to the angle of incidence of the illuminating light, such as in
reflection from a mirror.
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