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Glossary: M

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MD5 (checksum)
The MD5 hash algorithm is a commonly used function for validating data integrity. The name is derived from Message-Digest algorithm 5. The algorithm is applied against the source data (typically a file and its content) in order to generate a unique, 128-bit hash value (often called a checksum, although strictly speaking it is not one).…
See Hash algorithm
Megapixel
A megapixel is one million pixels, and is commonly abbreviated "MP." The megapixel count of a camera sensor is one of the most common characteristics used in describing and comparing digital cameras.…
See Pixel
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
Metadata
Information about an analog or digital object, a component of an object, or a coherent collection of objects. Metadata describing digital content is often structured (e.g., with tagging or markup) and it may be embedded (Metadata, embedded) within a single file, incorporated within the "packaging" that is associated with a group of files (e.g., METS),…
See Also Exif; IPTC Metadata; Metadata, administrative; Metadata, descriptive; Metadata, embedded; Metadata, file characteristics; Metadata, preservation; Metadata, process; Metadata, rights; Metadata, source; Metadata, structural; Metadata, technical; TIFF Header
Metadata, administrative
Metadata used for the management of digital content, such as information about rights and permissions (see Metadata, rights) as well as other facts about a given digital object. Some speakers define administrative metadata to include technical metadata (see Metadata, technical), source metadata (see Metadata, source), and process metadata (see Metadata, process).…
See Metadata
Metadata, descriptive
Descriptive metadata provides information about the intellectual or artistic content of an object and may also contain data describing the physical attributes of the object. Descriptive metadata supports specific user tasks, such as discovery and identification of content. In libraries, this category is sometimes called bibliographic metadata.…
See Metadata
Metadata, embedded
Embedded metadata is a component of a digital file that exists alongside the content (usually binary data) within the file, making the digital file self-describing. In the realm of still images, embedded metadata may conform to specifications like the following: Exif, IPTC Metadata, TIFF Header and XMP. Other elements or chunks found in…
See Metadata
Metadata, file characteristics
Technical information about a digital file or multifile digital object. For example, for digital photographs, this category includes the shutter speed and lens aperture; for all digital images, the category includes such things as pixel dimensions; for sound recordings, the category includes sampling frequency and bit depth. File-characteristics metadata is commonly embedded within image files…
See Also Metadata, technical; Metadata, source; Metadata, process
Metadata, preservation
Term strongly associated with the Preservation Metadata for Digital Materials (PREMIS) working group. The group defined a core preservation metadata set, supported by a data dictionary, and identified strategies for encoding, storing, and managing this metadata. Many data elements that are important for preservation are found in other categories, especially those classified as…
See Metadata
Metadata, process
Metadata that documents the details of the processes used to reformat (convert) or transcode content, called digital provenance (<digiprovmd>) in METS. For images, this subcategory can be documented in MIX and, for sound recordings, in AES-X98C, a draft standard from the Audio Engineering Society called Process History.…
See Also Metadata, technical; Metadata, source; Metadata, file characteristics
Metadata, rights
Metadata concerned with the limitations and restrictions regarding the access to and use of content. Common elements include copyright status, use restrictions, and information about licensing agreements. Rights metadata is often included as a component of administrative metadata (Metadata, administrative).…
See Metadata
Metadata, sidecar
See XMP sidecar file
Metadata, source
Metadata that documents the technical features of the item that has been reformatted (from analog) or transcoded (from digital). This category is called source metadata (<sourcemd>) in METS, where it is classified as a subtype of administrative metadata. For a photographic negative, source metadata might include the dimensions of the original and its minimum…
See Also Metadata, technical; Metadata, file characteristics; Metadata, process
Metadata, structural
In digital library community usage, structural metadata describes the intellectual or physical elements of a digital object. For a file that represents a single page as a compound document (e.g., a JPEG 2000 jpm file), the structural metadata may include information on page layout. In a multi-file digital object (e.g., a scanned book with many…
See Metadata
Metadata, technical
Generic term for technical information about the digital files and multifile objects, as further defined by three terms for important aspects of technical information: (1) file-characteristics metadata for technical information about the formatted digital file in hand; (2) source metadata for technical information about the source item, whether analog or digital; and (3) process metadata…
See Also Metadata, file characteristics; Metadata, process; Metadata, source
Metameric match
See Metamerism
Metamerism
A phenomenon exhibited by a pair of colors that appear visually identical under one or more sets of light sources, but appear different under light sources with different spectral power distributions. The classic example of this is donning a pair of socks that look identically colored under home lighting but exhibit different colors under natural…
Metrology
Specifically, metrology is the study of measurement. It is practically related to Quality Assurance and Quality Control in that it ensures devices used to measure quality or performance are giving accurate and precise readings.…
See Also Quality assurance; Quality control
Microfilm
According to an exhibition at the University of California, microphotography is as old as photography itself, with some experiments dating to 1839. Many other developments followed. The generic term microform covers reels of microfilm, sheet-form microfiche, aperture cards, and other types. The 1930s saw the first microfilming of newspapers, journals, books, and dissertations together…
See Microfilm standards
Microfilm standards
Libraries and archives standardized microfilming practices during the latter third of the twentieth century. The Library of Congress published two guidelines in the 1970s, followed by the publication of a number of standards in the decades that followed. (Slightly out of date references to these standards will be found on Web pages provided by…
See Microfilm
Micron
Abbreviated as µm, a micron is a unit of distance equal to one thousandth of a millimeter or one millionth of a meter. The micron is the standard unit of measure to describe the pixel size on an image sensor.…
Modulation Transfer Function
The sharpness of an imaging system can be characterized by its Modulation Transfer Function (MTF), which is generally equivalent to the Spatial Frequency Response (SFR). One approach to measuring this parameter employs a target with black and white bands of increasing spatial frequency (see examples at http://www.normankoren.com/Tutorials/MTF.html). (There are also other methods for measuring MTF…
See SFR
Moiré pattern
A repeating low frequency geometric pattern induced by the interaction of two out-of-phase geometries of higher frequency. Moiré often occurs upon display of digitized halftone patterns caused by the out-of-phase interaction of the halftone pattern and sensor geometries.…
See Also Distortion; Artifact (defect)
Monochromatic
Light characterized by having a single wavelength. In more general usage, light or an image composed of a single hue.…
Mosaic image
An image produced by combining numerous individual images into a single image. A mosaic image is produced by images that have been combined or stitched together in rows and columns, creating a single image from a matrix of images as opposed to a stiched panorama image. Also referred to as a photo montage…
Multichannel (audio)
A multichannel recording is a mixed and edited presentation in which various channels of sound have been assigned locations in a sound field ("left front loudspeaker, right rear loudspeaker"). In this glossary, multichannel is distinguished from multitrack, which is defined as the "raw" (unmixed, unedited) output from a recording session. Some audio…
See Also Channel (audio); Multitrack (audio)
Multitrack (audio)
A multitrack recording consists of multiple, separate streams of sound without defined locations in a sound field. During a typical music-recording session, individual instruments or voices will be recorded on separate tracks. When these multiple tracks are mixed at the end of the session, combinations of sounds are assigned places in a sound field…
See Also Track (audio); Sound field; Channel (audio); Multichannel (audio); Interleaved sample audio
Museum-quality facsimile or print
Elaborated subtype of the physical replica, generally produced for sale to the public (examples are listed as resources associated with this term). In the days of film-based reproductions, it would have been unusual for library and archive preservation programs to produce museum-quality facsimiles, although they might have joined forces with a publisher to do so.…
See Also Physical replica; Virtual replica; Copy negatives and transparencies;Interpositives duplicate negatives and transparencies