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Glossary: C

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Calibration
The comparison of instrument performance to a standard of higher accuracy. The standard is considered the reference and the more correct measure. Calibrations should be performed against a specified tolerance.…
CFA
See Also Color filter array; Bayer color filter array
Channel (audio)
A single stream of recorded sound with a location in a sound field ("left front loudspeaker"). This definition reflects common (although not universal) usage. Some writers use the term more broadly (no requirement for sound field location) or apply it to a signal that has been stored on media ("a two-channel tape"). …
See Also Track (audio); Multitrack (audio); Multichannel (audio); Sound field
Checksum
See Hash algorithm
Chromatic
In common terms, chromatic refers to light having the perceived quality of color, as opposed to achromatic. More specifically, chromatic has the quality of hue. All colors other than the neutral colors of gray, black and white are chromatic.…
Chromatic aberration
An image defect caused when different wavelengths of light are focused at different distances from a lens. This results in varying degrees of sharp focus at the image sensor depending on the color or wavelength of light. Chromatic aberration is seen as "color fringing," and is most noticeable in an image at edges with…
Chromaticity
The characteristics of color associated with hue and saturation without reference to the aspect of brightness.…
CIE
The International Commission on Illumination (French Commission Internationale de l\'Eclairage). The CIE is an international forum involved in matters relating to the science, technology and art of light and lighting. The CIE conducts research, publishes standards and procedures and provides guidelines related to light and lighting.…
CIE illuminant
See Standard illuminant
Clipping
The abrupt truncation of a signal when the signal exceeds a system\'s ability to differentiate signal values above or below a particular level. In the case of images, the result is that there is no differentiation of light tones when the clipping is at the high end of signal amplitude, and no differentiation of dark…
See Distortion
Clocking (digital audio)
Although this term applies to many digital signal creation and processing activities, the focus for this definition is sound recordings, especially their creation by a-to-d converters. The converter\'s reference clock determines when a sample is taken and, if the clock is not particularly stable, then the interval between samples will vary. The key difference…
See Also A-to-D converter; Jitter
CMYK
A subtractive color model used in printing that is based on cyan (C), magenta (M), yellow (Y) and black (K). These are typically referred to as process colors. Cyan absorbs the red component of white light, magenta absorbs green, and yellow absorbs blue. In theory, the mix of the three colors will produce black,…
See Color model
Codec
A codec is a software or hardware application that compresses and decompresses data, combining the functions of an encoder and decoder.…
See Also Encoder; Decoder
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
Color channel
A color channel stores the color information for one of the primary color components of a color model. For example, the RGB color model has three separate color channels; one for red, one for green and one for blue.…
Color constancy
The high level of invariance of the visual system to the perception of hue relative to changes in the level of variance of the color qualities of a luminant.…
Color depth
See Bit depth (image)
Color filter array
Digital image sensors used in scanners and digital cameras do not respond in a manner that differentiates color. The sensors respond to the intensity of light: the pixel that receives greater intensity produces a stronger signal. A color filter array (CFA) is a mosaic of color filters (generally red, green and blue) that overlays…
See Also Array; Bayer color filter array
Color fringing
See Chromatic aberration
Color gamut
See Gamut
Color management
The use of software, hardware and procedures to measure and control color in an imaging system, including capture and display devices.…
Color misregistration
Color-to-color spatial dislocation of otherwise spatially coincident color features of an imaged object.…
Color model
A color model is a way of specifying or describing a color numerically; common examples include RGB, HSV and CMYK. For example, in the 24-bit-deep RGB color model, the intensity of each of the red, green and blue components of the model (8 bits for each channel) are represented on a scale…
See Also Color; Gamut; CMYK; HSV; RGB; sRGB
Color SFR Difference
The differential spread of light between color channels. …
Color space
A geometric representation of colors in space (generally in three dimensions) can be visually perceived or generated using a particular color model.…
Color temperature
Color temperature is a simplified characterization of the visible spectral properties of a light source. It refers to the absolute temperature (in degrees Kelvin, i.e., Celsius-sized degree units above absolute zero) to which one would have to heat a theoretical "black body" source to produce light in a continuous spectrum and of a certain color.…
Colorimeter
An optical instrument for measuring colorimetric quantities. Colorimeters are the primary device used to evaluate the color qualities of display monitors. There are two basic types of colorimeters: tristimulus colorimeter and spectrocolorimeters.…
Colorimetry
The science of measuring color and color appearance.…
Compression (data)
The process of encoding data in a manner that reduces the amount of information required than required for the uncompressed data. Compression techniques can be categorized into two major categories: lossless and lossy.…
Compression ratio
The ratio of a files uncompressed size over its compressed size. A file compressed ten-fold over its uncompressed size would be described as having a ten-to-one compression, expressed as 10:1. Some formats such as JPEG and JPEG 2000 allow the user to specify the compression ratio.…
Compression, lossless
Data compressed using a lossless compression technique will allow the decompressed data to be exactly the same as the original data before compression, bit for bit. The compression of data is achieved by coding redundant data in a more efficient manner than in the uncompressed format. The Compression ratios that can be achieved with…
Compression, lossy
Data compressed using a lossy compression technique results in the loss of information. The decompressed data will not be identical to the original uncompressed data. Conservative lossless compression can result in a form of lossy compression referred to as visually lossless compression.…
Compression, visually lossless
A form or manner of lossy compression where the data that is lost after the file is compressed and decompressed is not detectable to the eye; the compressed data appearing identical to the uncompressed data.…
Continuous tone
Generally referring to pictorial images where there is a non-broken range of tones from white to black that may have every shade of gray represented. There are theoretically an infinite number of tones. Traditional photography (photochemical photography) produces continuous tone images. When reformatting pictorial items, it is important to distinguish continuous tone originals from…
See Printed halftone
Contrast
Any difference in luminance level between regions of interest …
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.…
Contrast stretching
Contrast stretching is an informal nickname for an enhancement that may be considered for derivative images of documents (and possibly some drawings); its simplest definition is "making paper lighter and writing darker." …
Copy negatives and transparencies
Pertains to the copying of pictorial works, maps, illustrative plates in books, posters, etc., i.e., items viewed by reflected light. In order to have the ability to produce prints that reproduce such works--in effect, to produce physical replicas--library and archive preservation programs formerly created photographic copy negatives (generally in black-and-white, rarely in color) or copy…
See Also Interpositives, duplicate negatives, and transparencies; Physical replica
Cropping
Cropping is an image-editing/processing technique whereby an unwanted portion or portions of a digital image are removed. Cropping is usually performed to remove some portion of one or more outside edges of the image. Cropping may be performed in different manners to the same image depending on its intended use. For example, on…
CSF
See Contrast Sensitivity Function (CSF)