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Glossary: D

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D50 is a designated CIE standard illuminant representing a daylight color temperature of 5,000 degrees Kelvin, corresponding to warm daylight near sunrise or sunset. D50 is the standard used in the graphics industry.…
See Also Standard illuminant; Color temperature
D65 is a designated CIE standard illuminant representing a daylight color temperature of 6,500 degrees Kelvin, corresponding to daylight near noon. The sRGB color space defines D65 as the illuminant for white.…
See Also Standard illuminant; Color temperature
Data rate
The number of bits that are conveyed or processed per unit of time, most often (but not exclusively) employed when discussing time-based media like sound or video. Often expressed in terms of kilobits per second (kbit/s or kbps, 10 to the third power), megabits per second (Mbit/s or Mbps, 10 to the…
See Decibel
De-mosaic interpolation
An image processing operation that estimates, through spatial interpolation, the count values of the unpopulated color pixels of a color filter array mosaic pattern.…
See De-mosaic interpolation
The decibel (dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity) relative to a specified or implied reference level. A decibel is one tenth of a bel (B). Although the term applies to digital data in a general way, most usage in a digital…
See Also Signal to noise ratio; Decibels relative to full scale
Decibels relative to full scale
The term dB FS (or dBFS) means decibels relative to full scale. It is used for amplitude levels in digital systems with a maximum available peak level, e.g., PCM encoding, where 0 dB FS is assigned to the maximum level. A signal that reaches 50 percent of the maximum level would, for example, have a…
See Decibel
An application or algorithm that decompresses data previously compressed by an encoder. …
See Encoder
An event or shortcoming that does not conform to specification. Defects are generally classed by severity, with class one being the highest severity.…
See Also Artifact (defect); Distortion
Delta E
A color difference metric that is intended to correlate with human visual judgments of small differences in perceived color between two color stimuli. The independent variables for the calculation use the values for the two color stimuli under consideration, expressed in terms of L*a*b* color space (sometimes called CIELAB, from the International Commission on…
Delta Sigma audio encoding (DSD)
Process for sampling an input signal. In the realm of digital content, this approach is generally seen as applied to sound, where it is often described as "oversampling." The delta-sigma (some say "sigma delta") converter digitizes the audio signal with a very low bit depth (generally 1-bit) but a very high sampling rate. The oversampling…
A device used to measure the amount of light reflected or transmitted by an object represented as density. The less the light is reflected or transmitted by an object, the higher its density. A transmission densitometer is used which measures the optical density of transparent materials such as negatives or slides while a a…
See Spectrodensitometer
Density can refer to either transmission density or reflection density. Transmission density refers to the opacity of the object and is measure of the percentage of light transmitted through the object when compared with the amount of light striking the object. The formula for calculating transmission density is Log10 1/T=D, where T = %…
See Densitometer
Depth of focus
The distance along the optical axis that remains within acceptable focus. …
Derivative file
Often called service, access, delivery, viewing, or output files, derivative files are by their nature secondary items, generally not considered to be permanent parts of an archival collection. To produce derivative files, organizations use the archival master file or the production master file as a data source and produce one or more derivatives, each optimized…
See Also Production master file; Archival master file
Descriptive metadata
See Metadata, descriptive
An image processing method to correct the skew exhibited in a digital image. Automated deskew functions are often features of scanning or OCR software applications.…
Digital Image Conformance Evaluation. A software application developed through funding of the Library of Congress. The DICE application provides detailed information on the performance characteristics of image targets. The application is designed to evaluate two types of image targets - a device target and an object target. The device target is imaged and evaluated…
Diffuse reflection
See Reflection, diffuse
Digital file
At a high level of abstraction, a digital or computer file is a stored segment or block of information that is available to a computer program. Files are so named because they are the counterparts of the paper documents traditionally kept in file folders, usually stored in a file cabinet. Computer operating systems consider files…
See Also Digital package; Digital package part
Digital image
The visual manifestation of a digitally encoded representation of the visual characteristics of an object. The term is also used as shorthand for a digital image file.…
Digital imaging
The process of creating digital images. The term may also be used more generally to include digital image processing .…
Digital negative
Digital object
See Object
Digital package
The set of files that comprise all of the parts of an item, e.g., the images for all the pages in a book or the sound files for both sides of a 78 rpm phonodisc. In addition, a package may include other files, e.g., the book\'s marked-up text, a transcription of the phonodisc\'s music,…
See Also Digital package part; Digital file; Representation (PREMIS term); Intellectual entity (PREMIS term); Object (PREMIS term)
Digital package part
One part of a digital package. Like the package itself, the digital item part is virtual or conceptual. It correlates to one part of the original item that has been reformatted. For example, a digital item part might represent a specific book page ("page 3") or the audio for side B of a…
See Also Digital package; Digital file
The process of recording an analog signal in a digital form. In relation to content of this site, it describes the process of translating analog signal data emanating from an object (light or sound) into a digitally encoded format. Audio, still and moving images are commonly digitized for increased access or for preservation purposes.…
See Digitization
Direct Stream Digital (DSD)
See Delta Sigma audio encoding (DSD)
The alteration of the original shape (or other characteristic) of an object, image, sound, waveform or other form of information or representation, usually unwanted.…
See Also Aliasing; Artifact (defect); Clipping; Defect; Distortion, geometric; Distortion, radiometric; Moiré pattern; Noise; Pixellation; Total harmonic distortion
Distortion, geometric
Distortion in which the true geometry of an object is not properly represented in the digital image, e.g., barrel (sides of a square bulge out) or pincushion (sides of a square curve inward). Some factors that can cause geometric distortion include: system optics, sensor defects, or mis-position of the image plane relative to the…
See Distortion
Distortion, intermodulation (audio)
See Intermodulation distortion (audio)
Distortion, radiometric
Distortion exhibited by incorrect luminance values in the pixels recorded in an image when compared to the reflectivity or density of the object being digitized.…
See Distortion
Distortion, total harmonic (audio)
See Total harmonic distortion
Dither is intentionally applied noise that is intended to randomize quantization error. This can have the effect of preventing visible or audible patterns in images and sounds such as contouring that are more objectionable than random noise. Dither is routinely used in processing of both digital audio and digital images.…
See Dither
Dmax / Dmin
Dmax is an abbreviation for maximum density and Dmin for minimum density. The abbreviations are used both in describing the characteristics of an image or an imaging device such as a scanner.…
Digital Negative (DNG) is a digital image file format designed by Adobe Systems. DNG is a file format that wraps camera sensor data ("camera RAW data") plus metadata to support image reconstruction, adjustment, and display based on the TIFF/EP standard. Thus it can be seen as a means to "normalize" a RAW…
Dots per inch
The reduction of an image's effective sampling frequency by means of image processing operations. …
DPI stands for dots per inch, and was originally used specifially as a term in printing, providing a measure of how many dots of ink are placed on a print in distance of one inch. The terms DPI and PPI (pixels per inch) are used somewhat interchangeably today, with scanner manufacturers often providing…
See Delta Sigma audio encoding (DSD)
Duotones results from halftone-printing a pictorial image (most often from a grayscale continuous tone image) in two different ink colors, thus producing a richer, longer tone scale than is possible using only one ink color.…
See Printed halftone
See Duplex scanner
Duplex scanner
A scanner that is able to automatically copy both sides of loose paper sheets. Many commercial sheetfed scanners have duplex capabilities.…
See Also Sheetfed scanner; Automatic document feeder
Duty cycle (scanner)
This term generally refers to the percentage of time a machine or piece of equipment can be in operation in relation to the time it must remain out of operation. For instance, a duty cycle of 100 percent means that the equipment will operate continuously (24x7). A duty cyle of 30 percent means it…
Dynamic range
Term used to describe the ratio between the smallest and largest possible values of a changeable quantity, frequently encountered in imaging or recorded sound. Dynamic range is another way of stating the maximum signal-to-noise ratio. To use sound as the example, this is the ratio of the loudest (undistorted) signal to that of the quietest…
See Also Bit depth (image); Bit depth (audio); Decibel; Gamma; Gamma correction; High dynamic range imaging; Signal-to-noise ratio
Dynamic thresholding
See Thresholding, adaptive