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Photopic sensitivity
Photopic sensitivity refers to visual sensitivity under conditions of bright light, where radiant energy stimulates the cones (retinal photo-receptors responsible for color perception). Photopic spectral sensitivity differs from scotopic spectral sensitivity (see scotopic sensitivity).…
See Also Photopic (general); Scotopic sensitivity; Mesotopic sensitivity
Mesopic sensitivity
Mesopic sensitivity refers to visual sensitivity under conditions of intermediate light levels, where radiant energy stimulates both the rods and the cones (the two types of retinal photo-receptors). Mesopic vision is a combination of photopic vision (see photopic general) and scotopic vision (see scotopic sensitivity).…
See Also Photopic (general); Scotopic sensitivity
Photopic (general)
Having sensitivity characteristic similar to the human eye response.…
See Also Photopic sensitivity; Mesopic sensitivity; Scotopic sensitivity
Visible spectrum
The band of electromagnetic radiation that human eyes can detect. This ranges from wavelengths of approximately 400 to approximately 700 nanometers (nm). Normal human vision responds slightly beyond this range to both shorter and longer wavelength radiation, but with very little sensitivity. Maximum sensitivity of the human vision in bright-light conditions is…
Scotopic sensitivity
Scotopic sensitivity refers to visual sensitivity under conditions of low light, where radiant energy stimulates the rods (retinal photo-receptors that are achromatic, containing only one type of pigment). Scotopic vision does not involve the perception of color.…
See Also Photopic sensitivity; Mesopic sensitivity
ISO (film speed)
Used colloquially in the context of film photography, ISO followed by a number (e.g., 400) represented the sensitivity of a given film emulsion to light, often referred to as "film speed." Higher ISO numbers indicated a greater sensitivity to light. The emulsion speed sensitivity was determined by the standards of the International Standards Organization…
See ISO (Standards Organization)
Contrast Sensitivity Function (CSF)
A functional description of the visual systems threshold sensitivity to peak-to-peak luminance differences ( i.e., contrast) of a range of sine wave spatial frequencies. While the CSF is dependent on the average luminance viewing conditions, a single one is usually adopted for typical conditions.…
Sensitivity
The reciprocal of the amount of light necessary to achieve a desired output response.…
Acutance
An objective SFR-derived metric weighted by the Contrast Sensitivity Function (CSF) used to predict the subjective impression of sharpness.…
Flat fielding
Process that corrects for irregularities in pixel values caused by variations in pixel sensitivity in the camera sensor, dust or damage on a lens, uneven lighting, or distortions in the optical path to produce an image of uniform brightness. Flat fielding software can reduce non-uniformity in images. Lenses designed specifically for digital flat field imaging…
Photometry
Photometry is the science of measuring the intensity of light (luminous intensity) in relation to the sensitivity of the human eye. Photometry is analogous to radiometry, weighted by the response function of the eye. The science of photometry does not deal with the perception of color, which is the realm of colorimetry.…
Gain (image)
In practical discussions of digital cameras and scanning devices, gain is described as a means of increasing the ISO of the device and apparent sensitivity to light. In more technical terms, gain in a digital imaging device represents the relationship between the number of electrons acquired on an image sensor and the analog-to-digital units (ADUs)…
Color
Color is one of the most difficult areas in digital imaging to specify, digitally encode, and reproduce, and for the verification that specifications have been met. The primary reason it is so challenging is that color is a perceptual phenomenon and cannot be described in an absolute and objective manner as can many other…
See Also Color model; Gamut; Spectral power distribution; Metamerism

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