Multiple speaker audio system used to deliver 'surround sound'. Uses 5 'satellite' speakers - Centre, Front Left, Front Right, Left Surround & Right Surround (rear speakers), and subwoofer(s) for the single low frequency effects (LFE) channel, hence '5.1'.
Most common consumer or 'home theatre' surround format. Can be compressed using Dolby AC-3.
Advanced Audio Coding. Lossy compression technique for audio which uses perceptual modelling. Allows file size reduction with minimal audible side-effects. Part of MPEG-2 and MPEG-4 standards. For full explanation see AAC - Advanced Audio Coding.
Art and Architecture Thesaurus, a structured vocabulary relating to fine art, architecture and decorative arts.
Consideration given to ensure that a service (web site etc.) is made available to users whether or not they have a disability.
Based on red, green and blue light which when all combined in equal amounts will appear white. Varying the combination of these three hues creates other colours. Computer monitors and televisions are the most common applications of additive colour.
A sequence of instructions (usually to a computer) to process the data set of an object according to a defined set of rules. e.g. compression of file sizes.
Errors introduced during the digitisation process, a result of the fact that digital recording of sound or image takes discrete samples as opposed to continuous measurements. Aliasing errors in the audio domain can result in unwanted frequencies which may be eliminated by filtering out all sound above some frequency. Examples of aliasing errors in the still and moving image domains include Moiré and jaggies. They can be ameliorated by changing the size of the samples or changing the colour information of pixels where the error is apparent. See also anti-alias.
This is the existing light found in a scene before the photographer introduces additional lights. Also referred to as available light.
Any method of storing information where the changes in value of the characteristics of the source are modelled in a different medium. Thus the vibrations of sound waves may be recorded as wavy grooves on an LP and the variations in light intensity on a television as varying degrees of magentisation on a tape. See also digital.
animated raster image
A term used to denote an unwanted feature in a digital image, recording or moving image which was introduced in the process of converting it to its digital form , e.g during scanning, conversion or compression.
Refers to the relationship between the width and height of an image or screen - e.g. 4:3 means for every 4 units the screen is wide, it will be 3 units high. Common aspect ratios are 4:3 and 16:9 (video); 4:3 and 3:2 (photography); 1.85:1 and 2.39:1 (cinema).
A recording of the ambient noise of a location. Useful in video editing to fill in places where the sound has been removed.
automatic sheet feeder
A device attached to a scanner, printer or photocopier which enables automatic processing of large numbers of documents.
An artefact in an image or moving image where a gradual change in colour or brightness is replaced by a series of discrete, visible changes, e.g. when a printer fails to recreate a subtle gradient of tone or colour a banded area of flat colours are printed instead.
In digital systems bandwidth is a measure of data speed, usually measured in megabits per second. The higher the bandwidth, the faster data files can be transferred or processed. Colloquially, bandwidth is used to refer to the overall speed of a system, as in, “We don’t have the bandwidth to process all of those images in one day.”
This is an optical distortion common to wide angle lenses where the centre of the image appears larger than the edges. With rectangular camera formats this distortion gives rectangular subjects a barrel shape.
As opposed to processing a data file individually, in batch processing a number of files are collected together and sent for processing at the same time (perhaps overnight), thus requiring less operator attention.
A grid of red, blue and green elements used to enable a single-chip CCD to record colour imformation. By determining the colour of light which can reach each sensor it dedicates half of the chip’s elements to the recording of green light (which is effectively the luminance of the image) with the other half equally divided between red and blue (effectively the chrominance of the image).
Business and Community Engagement - see JISC website for further details.
A sample of the file or job which can be used as a reference to measure subsequent work against. During the feasibility study, benchmarks should be set to determine the technical standards to which the material should be digitised. Quality Assurance procedures should measure the digitised images against these benchmarks.
Magnetic video recording format developed by Sony. The dominant format used in the broadcast industry during the 1980s and 90s. Still in use in non-broadcast sectors. Not to be confused with Betamax.
Magnetic video recording format developed by Sony. Lost the home video recording format war to VHS, despite some early technical advantages (e.g. hi-fi, superior picture quality). Generally regarded as obsolete but is still in use by dedicated enthusiasts. Not to be confused with Betacam.
Anything which is binary has only two possible values. All computer data is represented in binary form, as a series of bits which have the value 0 or 1.
The bit depth of an image (also known as colour depth) refers to the number of bits used to describe the colour of each pixel - see colour depth for more on this. For audio, bit depth refers to the number of bits used in a recorded sample and determines the range of values available per sample. Not to be confused with bit rate. See also our Introduction to Digital Audio for more details.
See Raster Image.
Bit rate, which is commonly confused with bit depth, refers to the rate at which digital data is transferred or processed (most commonly bits per second). In audio and video it refers to the amount of information (number of bits) stored per second, e.g. 192 kilobits per second (typical mp3 audio) or 10 megabits per second (typical DVD video). See also our Introduction to Digital Audio for more details.
The British Library
The combination of established methods of teaching and learning, with methods supported by digital technology - online learning, e-learning, mobile learning, remote learning.
Blu-ray is a storage medium and does not refer to a specific type of data on that medium. It is commonly used for video and data storage and has a capacity of 25 GB in its single-layer format.
Used in combination with digital cameras, a directional microphone is attached to the end of a long pole or ‘boom' and can then be held just out of shot by the boom operator and directed towards the subject(s). If used in combination with a radio transmitter - as is increasingly common - the radio receiver is then connected to the camera/recorder microphone input.
In digital terms, increasing the brightness of an image means increasing the colour components of each pixel without changing the relative amounts so that no hues are altered.
Broadcast Wave Format. An extended form of WAV audio file, with an additional data header used for storing metadata and synchronisation data to describe the audio. Metadata chunk usually in BEXT or iXML format. Standard audio archival format.
Computer Aided Design - a type of software widely used in design and architecture to assist in precise draftsmanship and allow greater options in how the design can be viewed, e.g 3-D models, 3-D images, moving perspective.
Short for camera-recorder. A video camera which has the recording apparatus built into the camera. This is now the norm for all video cameras save for those used in a multi-camera situation where the signals from all the cameras will be sent to a single location where they can be individually recorded and/ or mixed for recording or immediate broadcast.
Movement of the camera during an exposure, this leads to a bluring of the image. A faster shutter speed or stable camera support such as a tripod will normally resolve the problem.
The acquisition of data in a digital form, be it a digital recording, image or moving image.
An electronic device which captures digital images, audio or video. Capture devices include flatbed scanners, drum scanners, film scanners and digital cameras, digital recording software and video digitising hardware.
Content-based image retrieval, a retrieval method where pictures are located using the image content rather than with the metadata.
The CD (compact disc) is a storage medium and does not refer to a specific type of data on that medium: CDs were originally designed for audio recordings, but can store video of any other type of data. They have a maximum capacity of around 800 MB. Various other, newer media are competing with the CD in different areas ( DVD for data, DVD and Blu-ray for video, SACD and Flash memory for audio).
Compact disk read-only memory, a system for recording, storing, and retrieving data on a compact disk. This can then be read using an optical drive. A CD-ROM can only be written once. Compare with CD-RW.
A method of reducing the amount of data needed to represent an image. The idea of chroma subsampling stems from the fact that the human eye is far less sensitive to colour information ( chrominance) than it is to brightness information ( luminance). Thus far less colour information need be recorded than brightness information and a good quality image will still result. The degree of chroma subsampling is represented as a ratio of three numbers. No subsampling gives a ratio of 4:4:4, while DigiBeta and DV use, respectively, 4:2:2 and 4:2:0 subsampling. A Bayer filter is a physical means of implementing a chroma subsample of 4:2:2, though with a different arrangement of samples than with DigiBeta.
When the value of a datum is greater or smaller than the maximum or minimum that can be represented by the format in which it’s stored, we say it’s been clipped. For example, each colour of a pixel may have a value of from 0 to 255. Any values which are brighter than 255 will still be represented as 255. Thus, in an image or a video an overly bright image may have its brightest parts represented by a solid white area. Similarly, a very loud recording may have its loudest portions represented by a constant period of maximum volume. In audio recordings this has the added effect of creating a usually unwanted high-frequency distortion, although the creative use of this distortion has been a staple of electronic music, both popular and classical, for decades.
A common tool found in image optimisation programs which allows image data to be sampled and placed elsewhere in a picture. Often used to remove blemishes from an image.
Complementary metal oxide semiconductor, a type of semiconductor technology used for the detector within a digital camera.
Colour management system, the calibration of system components which allows predictability in colour reproduction and consistency of performance.
Cyan, magenta, yellow and black, the four ink colours of the subtractive colour system used in printing. The letter K is used for black because B is used for blue in other acronyms relating to colour systems.
Abbreviation of coder-decoder: a program which encodes or decodes data. Codecs are most commonly encountered in the digital audio and video domains, where they are used in the manipulation of audio and video data. A codec that decodes from one format and immediately re-encodes it in another is called a transcoder.
Fidelity of colour in the scanned image with that in the original.
colour cast removal
Removal of an unwanted 'wash' of colour, performed in an image editing application.
Performed with image editing software or scanning software, ensuring scanned colour fidelity with the original.
The colour depth of an image (also known as bit depth) refers to the number of bits used to describe the colour of each pixel. Greater bit depth allows more colours to be used in the colour palette for the image. 8 bits per pixel will allow 256 colours, while 8 bits per colour component in an RGB image will allow 16,777,216 colours (256 red x 256 blue x 256 green), usually referred to as "millions of colours." See also bit depth.
colour look-up table
A table containing the RGB values for 256 colours. Storage space is saved as each pixel needs only an 8 bit number to reference a colour in the lookup table rather than that colour’s actual 24 bit value. See also palette.
The degree to which gradations in colour are represented in a storage method. For example, a system which allows 256 different values of red will have higher colour resolution than one which only allows 8 different values. As colour resolution increases, so does the size of the data needed to represent it. See also bit depth.
Or colour model. Mathematical definitions of colour used for aiding communication of colour information.
A measure of the colour quality of a specific light source and is measured in degrees kelvin (K). Lower colour temperatures such as tungsten lighting at 2700 to 3300K have a warm yellow bias while higher values such as noon sunlight at 6500K have a cooler hue.
A type of analogue or digital video signal format. Component ins and outs are normally sets of three BNC connectors. Component signals carry picture only, are very high quality and are generally only found in high-end professional equipment. Common component signals include RGB, YUV and YIQ. See also composite, S-video, IEEE 1394 and USB.
A type of analogue video signal format. Composite ins and outs are normally either single phono connectors or mini-jacks. Composite signals carry picture only and are the lowest quality format. See also S-video, component, IEEE 1394 and and USB.
content management system
A content management system helps the user to view, manage, edit and distribute files in their collection. A content management system for digital images is sometimes referred to as an image management system.
Increasing or decreasing the difference between the lightest and darkest areas of an image.
In metadata, a set of correct values that a datum can have. For example, the datum ‘Month’ might be defined only to accept the values ‘January', 'February' etc. A thesaurus is an example of a controlled vocabulary document.
Copyright is an intellectual property right that protects the creator or owner of a work by regulating the use of that work.
Reduction in the dimensions of an image or video, possibly to remove artefacts created during digitisation (e.g. borders created during the scanning process) or simply to change the content of the image or video.
Crosstalk is an example of an artefact. In digital images or video it can refer to the bleeding of bright areas into darker ones or vice versa. In audio it commonly refers to sound from one channel bleeding over into other channels.
A powerful tonal adjustment function found in some scanner drivers and image optimisation programs.
In video and filmmaking, a shot of something other than the main subject or action of a scene. Cutaways are shot to provide the editor with material to insert in an edited scene (i.e. "to cut away to") to cover discontinuities in the main shot, such as when a portion of a person's speech is edited out. See noddy.
database management system
Software that controls the organisation, storage, retrieval, security and integrity of data in a database.
Digital Audio Workstation. A computer-based media production and/or editing system. Consists, as a minimum, of computer, audio and/or video recording software, and audio interface.
Dewey decimal classification. A numerical system for classification, originally devised for the classification of books.
A copy of the original digital file used for delivery purposes. This could be an identical copy of the original file or perhaps a lower quality version with a smaller file size suited for delivery over the Internet. See also master archive, access images and surrogate image.
depth of field
While camera lenses focus on a specific point at a specific distance from the lens the image may also appear sharp in front and behind the focus point. This distance of acceptable sharpness is know as depth of field and it can be increased or reduced by adjusting the size of the camera's aperture.
Removal, during scanning, of the matrix of dots in printed materials.
Correction of distortion caused by image capture from a viewpoint other than on the perpendicular.
A piece of software on a computer which enables it to communicate with and control a device connected to it such as a scanner or printer.
A professional digital video format. DigiBeta is a standard in the broadcast industry because of its excellent picture qualities and extremely robust nature.
Any method of storing information where the changes in value of characteristics of the source are converted into numerical data which is then recorded: in effect we record instructions to recreate the information rather than a model of that information. See also analogue.
A camera that does not contain any film but records the image as a digital object. The image is then downloaded into a computer system.
An image, whether displayed on a monitor, projected on a screen or printed on a sheet of paper, which has been created from a data file which contains colour information for all of the pixels which make up the image.
A term used generally to describe the process of creating and manipulating digital images
A visible or invisible mark added to a digital image which identifies its ownership. Visible watermarks are often used to prevent unauthorised use of copyright images.
See image capture.
Directionality and Pick-up Patterns
An important feature of any microphone is its pick-up pattern - how sensitive it is to sounds coming from different directions around it. This is represented as a polar diagram, usually taken to be a view of the microphone’s pattern as seen from above, with the microphone positioned at the centre of the circle.
Thus an omnidirectional microphone, which is equally sensitive to sound from any direction, has a circular pattern. A directional microphone has greatest sensitivity at the front, reducing as the source goes ‘off axis’, until reaching its minimum sensitivity directly behind; this produces a heart-shaped or ‘cardiod’ pattern.
Precise patterns will vary between microphones or even different frequency ranges on the same microphone, though they will all be variations of the generic pattern for that microphone. For example a cardioid directional microphone may be more directional at high frequencies than low. More expensive microphones may be supplied with a polar and/or frequency plot for that particular microphone.
This is common with wide angle lenses, though can also be seen with longer lens. The most common types of image distortions are 'barrel' and 'pincushion'. Barrel distortion will make a rectangular subject appear swollen in the middle while pincushion distortion will make it appear pinched.
The darkest tone that can be printed or displayed.
Digital negative graphics, an open source format under development by Adobe.
A piece of hardware that is mounted on a flat bed scanner to assist in scanning a number of unbound pages automatically.
Compressed audio format for encoding 5.1 surround sound. Widely used in cinema and for commercial DVDs. Developed by Dolby corporation.
An increase in the size of a printed dot, due to paper absorbency, ink type and temperature.
Digital rights management, strategies or technologies that are intended to protect digital resources from illegal copying or unauthorised access.
A 'high end' device using photomultiplier tube technology to capture images which are mounted on a cylinder.
A consumer digital video format. Note that the DV format supports both the PAL and NTSC standards and that an NTSC DV camera (i.e. one purchased in North America, for example) is not compatible with UK televisions (although a black and white picture may be viewable). See also DVCAM.
Digital Video Broadcasting-Terrestrial. A technical standard specifying the framing structure, channel coding and modulation for digital terrestrial television broadcasting in Europe. See DVB (Digital Video Broadcasting Project) website for further details.
A prosumer and low-end professional digital video format. It is almost identical to DV but is a bit more robust. DVCAM tapes can be used in DV cameras and vice versa, although the manufacturers warn against this.
The DVD (digital versatile disc, originally digital video disc) is a storage medium and does not refer to a specific type of data on that medium. It is commonly used for video recording and data storage, having a maximum capacity of around 4.7GB (higher when double-sided or double-layer). While it at first glance resembles a CD the two media are incompatible.
Referring to the range of values a datum can have. In the case of images or video it refers to the difference between the brightest and darkest parts of an image. In the case of audio, it refers to the difference between the loudest undistorted sound and the quietest audible sound.
Automatic brightness adjustment during the scan.
A JISC-funded national datacentre based at Edinburgh University Data Library. EDINA (not an acronym) is the ancient and poetic name for Edinburgh, Scotland.
In the most general sense, encoding is simply the conversion of information from one format into another. Thus a film camera can be said to encode the patterns of light passing through the lens into an arrangement of crystals on a piece of photographic film. More commonly we use the term to refer to the re-conversion of information from one digital into another digital format, often with some form of compression. See codec.
error detection and correction
File formats, optical storage media (CDs, DVDs) and hard drives use error detection and correction techniques to deal with data loss or corruption. Information can be lost from digital files through such things as incorrect copying, deterioration of media, human error and computer malfunction. In order to deal with such losses, redundant information can be stored in digital files which enables the user (a) to determine that errors have occurred (error detection) and (b) to repair these errors (error correction). Examples of such methods include parity bits, cyclic redundancy checking and various types of RAID storage.
Exchangeable image file format stores capture data such as shutter speed, aperture, ISO and lens type in the image file.
A preliminary study undertaken before the real work of a project starts to ascertain the likelihood of the project's success.
The way that data is represented and organised in a computer file.
The Apple Computer Corporation’s name for the IEEE 1394 interface.
Tape recorders pass magnetic tape over a recording head, which creates a pattern of magnetisation on the tape to store the audio or video information being recorded. In the case of most audio recorders the tape moves over the recording head and the head itself does not move. Recorders that have a higher bandwidth of information to record (e.g. video recorders and some digital audio recorders) often use a rotating head. See helical scan.
Adobe Flash is the 'industry standard' software for producing and displaying animation on the web. Flash can be used for everything from simple 2D animations to interactive 'rich content' web sites, video, and mobile device content. An example of a simple 'interactive' Flash animation can be seen in our Using Images in Education advice document.
Generic term used to describe compact storage devices used in digital cameras.
A digitisation device delivering scanned image data to a computer, the glass face on which the original is placed being flat.
Refers to the private copying of a legally owned work (e.g. music CD) into another format for playback on another device (e.g. MP3 player). UK law currently does not allow this, but the Gowers Review of Intellectual Property recommended a limited form of format shifting.
The rate at which video and film cameras make consecutive images, measured in number of frames per second (fps).
The dimensions of an individual frame in a still or moving image. The size depends on the film format. See also aspect ratio.
Not to be confused with Open Source software, free software is software which does not cost anything to acquire or use. Often, but not always, free software will consist of cut-down or demonstration versions of purchasable software. Such free software will serve either to generate goodwill in the prospective buyer or to advertise the purchasable version.
A popular example of free software which is not open source is the AVG Anti-Virus Free Edition, which has had tens of millions of downloads since its inception. Perhaps the most famous example of free software which is open source is the Linux operating system (although Linux is sold by companies which provide additional services with it, the OS itself is free).
This relates to how sensitive a microphone is to sounds at different frequencies. The human ear has a frequency response of around 20Hertz (20 cycles per second) - a very low tone to shake your fillings out - to 20kiloHertz (20,000 cycles per second) - a very high pitched whine. High frequency hearing decreases with age and prolonged exposure to loud noise.
Some microphones - especially good quality condensers - can pick up this entire range and beyond fairly evenly, but cheaper designs may sound ‘duller’ if their high frequency response is less extended, or ‘tinny’ if they do not capture low frequencies well. Some designs of microphone will accentuate a certain frequency range, making them suitable for particular jobs, but for vocal recording you will usually want a wide and fairly even (or ‘flat’) response.
Many good microphones come with a ‘frequency plot’, which will give an idea of their frequency response. These two examples show how the two microphones accentuate different frequencies in the 3-12 kHz range, and show markedly different treble and bass ‘roll-off’, with the SM58’s response curtailed at both extremes (which incidentally makes it a very popular live vocal mic, with good feedback rejection, but generally a poor recording microphone - unless you are Bono), and far better extension from even a relatively inexpensive condenser.
If the possible values of light coming from the subject of a photograph are plotted against the values by which that light is represented in a photograph, the resulting curve is called the gamma. Informally, the gamma of a medium is the way in which its representation of a subject differs from the subject itself. Since perfect representation is not possible, gamma can be seen to be describing an artefact of the image.
Used to calibrate devices, smoothing out any irregularities between input and output signals.
Graphic Interchange Format, a bitmap file format widely used on the Web. It has a limited colour palette (256 colours) which makes it more suited to graphics rather than photographs. It can also be used for limited animation.
In a photograph, grain can be thought of as the amount of noise in the image. On photographic film it is the inaccuracy in the recording of the image due to the clumping of the silver atoms, present after exposure and development. In the print it will appear as the negative of this - the printed gaps between the clumps. In photographic film there is an inverse correlation between grain and film speed: the faster a photographic film is, the grainier the images it reproduces will be.
A number of greys ranging from black to white. An 8 bit greyscale image could have 254 greys plus black and white for a total of 256 possible values. See also bitonal.
A hand-held, generally low quality, device for digitising images.
Methods employed to handle the original materials during the process of digitisation that result in minimal damage to the object.
Human computer interface or human computer interaction.
High-definition video generally refers to video with either 720 or 1080 lines, either interlaced or progressive. The definition is necessarily vague due to differing standards in a number of countries as well as ongoing changes in the video world. See also SD.
Because video and digital audio require greater bandwidth than analogue audio and consequently much higher recording speeds, they use rotating tape heads. The high speed rotating head is tilted so the slow moving tape passes at an angle (helical scan), recording the signal across the tape in diagonal stripes. The combination of the tape's movement over the head and the head's rotation permit the recording of data at a much higher rate than with a fixed head recorder. Recording at the same rate with a fixed head would require the tape to pass over the head at an extremely high speed. This would be impractical both because of the amount of tape needed and the difficulty of moving the tape at such a speed.
helical scanning head
See helical scan.
Hypertext Markup Language, a compupter language derived from SGML and used to write pages for the World Wide Web.
The Sony Equipment Corporation’s name for the IEEE 1394 interface.
International Association of Sound and Audiovisual Archives. Authority on archiving best practice for audio and video resources.
International Colour Consortium. The ICC have developed a cross platform, independent system of colour management based on profiles.
A type of digital video signal format. IEEE 1394 has two different types of connector which are unique to it. Unlike analogue formats, the IEEE 1394 format carries both picture and sound. It is found on many consumer and prosumer camcorders but in many less expensive models in recent years has been replaced with and USB. See also composite, S-video and component.
Institute for Learning and Research Technology, hosted at the University of Bristol.
Collection of images kept in secure storage.
Place where image files are kept in an organised form. Software that facilitates organised storage and retrieval of digital images.
Length of time over which an image serves a purpose or length of time before degradation begins.
image management system
Modification of images. Digitally this would be through the use of image manipulation or editing software. In print-based photography it might refer to the way the image is printed.
Type of original, e.g. painting, photograph, 35mm slide, etc.
Corrections made to a digital image to make it more closely match the original. Optimisation can also involve preparing the image for final delivery.
Making use of services available within an organisation.
The identification and labelling of data to assist in archiving and retrieval.
Continuance of intellectual content from original into the digital image.
intellectual property rights
Automatic rights afforded to a creator giving him or her economic rights of control over copying, adaptation and issuance of copies to the public.
This refers to a type of television signal where only half of the picture is redrawn at each refresh, either all the odd-numbered or even-numbered lines. Thus an interlaced signal at 50fps actually only redraws a complete picture 25 times over the course of a second. See also progressive.
If a datum, instead of being measured, is calculated based upon the data either side of it, it is said to be interpolated. Thus, for example, the effective resolution of a scanner could be increased if between each of the pixels it measures we create an additional pixel with values mid-way between its neighbours. Note that this can add errors such as the softening of hard edges since the calculated value isn’t necessarily correct. This is an artefact of this type of digitisation.
inverse square law
The inverse square law is commonly used in sound, photography and video to predict how energy will reduce as distance between the source and the measuring device increases. As the distance between an energy source and the point of measurement doubles the amount of measurable energy is quartered. In photography for example, the user can increase or decrease the intensity of light by moving the source closer or further away from the subject. The law is also regularly used in sound for example, if the distance between a microphone and the sound source is doubled the sound volume measured by the microphone is quartered.
Also known as aliasing or staircasing, these refer to the stepped effect observed along a diagonal line of square pixels. Especially apparent in low resolution graphical images, jaggies can be reduced or eliminated by the application of anti-aliasing techniques.
Open source file validation program available from the Library of Congress, intended to be integrated into archiving workflow.
The JISC TechDIS service aims to be the leading educational advisory service, working across the UK, in the fields of accessibility and inclusion. Their mission is to support the education sector in achieving greater accessibility and inclusion by stimulating innovation and providing expert advice and guidance on disability and technology.
JPEG or JPG
An image compression file format named after the Joint Photographic Experts Group who devised it. The JPEG format compresses images but sacrifices image detail ( lossy compression). See also Motion-JPEG.
JPEG 2000 or JP2
Searching text, in metadata associated with images, for a descriptive word.
Low Frequency Effects. Low frequency '1' channel of surround formats 5.1, 7.1 etc
If light shines directly on a lens it will normally produce a series of bright circular shapes accross the image and degrade the contrast. This is referred to as lens flare and can be reduced or eliminated by using a lens hood or shade.
A feature offered by some digital SLR cameras which allows the LCD screen to be used to compose an image instead of the eyepiece. It is often used to check focus under magnification. The live video feed to the LCD screen has resulted in some cameras now offering direct video capture.
A compression algorithm that reduces file size by actually removing imformation from the image, audio or video signal. The media object reconstituted from a lossy compressed file is different from the original uncompressed object, even though they may look or sound identical ( visually lossless).
Is the International System of Units (SI) unit of measurement for the intensity of light.
See Motion JPEG.
Alternative file extension for audio MP4 files. Introduced by Apple to indicate MP4 files with audio bias, but essentially identical in form and content to an MP4.
Machine readable cataloguing, a standard bibliographic format used in libraries.
A collection of digital files (images, video, audio) which have been stored in their original captured state. These master files are also referred to as master copies, preservation masters or preservation copies. See delivery copy.
See master archive.
Descriptive textual data associated with a data file.
A file containing information that describes or specifies another file.
A change from one hardware or software technology to another. For example, a database may be moved to a newer, faster server.
An interference pattern which may occur when scanning images with a halftone screen. An example of aliasing error.
Descriptive of an image which is made up of only one colour in varying brightness. Conventional black and white photographic images are monochrome: the single colour which is varied is most often grey or sepia, but any colour could be used and the result will still be monchrome. See also greyscale and bitonal.
Like a tripod but with only one leg. The photographer provides the other two legs to make a stable base for the camera.
Gained after copyright clearance has been gained and may be concerned with derogatory use of images, not crediting the creator, use of only part of an image etc. Must be asserted by creator.
An abbreviation of MPEG-1 Layer 3. A lossy compression technique for audio files, using perceptual modelling to reduce audio complexity and thus file size. Wide use for delivering audio (music, podcast etc) via the internet. ID3 tagging/metadata system. Superceded by AAC. See our User Guide to MP3.
Official file extension of files complying to MPEG-4 standard. Often contains video and/or audio, but can be any combination of media and metadata.
This is a large collection of compression standards used for everything from mobile phones to high-definition video. See also MPEG.
multiplexing / de-multiplexing
Multiplexing (aka 'muxing') is the process of interleaving small sections or 'blocks' of different file types - e.g. video, audio and subtitle text - into a single data stream, to allow simultaneous playback. De-multiplexing (or 'demuxing') is the reverse process of separating the individual data streams for decoding and playback. Muxing of two streams can be likened to the interlocking of the teeth of a zip.
ND (neutral density) filter
A filter which is placed in front of the lens or the lightsource to absorb light and reduce shutter speeds or allow the use of wider apertures.
A scanner accessed and operated over a computer network, shared by a number of users.
Non-Linear Editor. Video or audio software editing environment where video and/or audio 'tracks' or 'regions' can be edited and re-arranged in a non-linear, random access way.
A type of cutaway, a noddy is a shot of an interviewer nodding their head (or smiling, frowning, looking interested, etc.) and is a standard part of shooting an interview.
Any unwanted information introduced into data during the process of digitising or converting it is referred to as noise. In the case of audio data this may actually be noise, while in images and moving images it may refer to bright specks, snow, etc. Care should be taken to minimise the introduction of noise during digitising and transferring as it is either impossible to remove or only removable by degrading the data in other ways.
National Preservation Office - the old name for the British Library Preservation Advisory Centre
Nyquist sampling theorem
Also called the Nyquist-Shannon sampling theorem, it states that an analogue audio signal which does not go above N hz in frequency can be exactly reproduced digitally if the sampling rate of the digital recording is at least 2N Hz. Note that this is a theoretical result; in particular, for it to be true requires the samples taken to be infinitely large. it is nonetheless a good approximation of the limits of digital recording.
Open Archives Initiative Object Reuse and Exchange.
Not to be confused with Free Software, open source means that the actual code of the software is publicly and freely available. This means that anyone is free to modify the code and hence the workings of the software. As a result, open source software is usually, though not always, maintained by a (possibly quite large) group of volunteers. Even when the software is maintained by a private company (e.g. Moodle), the fact that it is open source means that suggestions and modifications can be made by anyone, and these changes may be incorporated into the official versions of the software by the maintaining company.
Open source software is often free as well, and when it is not free, the cost is generally very low. It should also be noted that open source software is not in the public domain, i.e. unlicensed. Rather, open source software is available under a licence (such as the GNU General Public Licence) which generally prevents users from incorporating it into proprietary products.
There are two important strengths to open source software. The first is that, since the creators/maintainers have no vested interest in keeping their code proprietary, decisions about the software are made solely to improve the software and not to protect its confidential nature. For example, a large corporation that makes a word processing package will change its file format frequently, either to make it difficult for its competitors to keep their products compatible with it or to require users to pay for new versions. Maintainers of an open source word processing package have no such motivation and hence changes made to the software will be done purely to improve the software.
The second strength is that it is unlikely that the software will ever cease to be supported. When a piece of software is proprietary to a private company, it may at any time decide to stop supporting the software at which point bugs will cease to be fixed and improvements to be made. With open source software, as long as there are programmers who are interested in maintaining the software there will be support for it. In fact, some software companies have made their products open source upon ceasing to provide support for them in order that such continuing support can flourish.
Sometimes free open source software will be sold by companies who add features such as ease of installation and technical support; a popular example of this is the versions of Linux sold by Red Hat. Linux is itself both free and open source.
A typical example of open source which is not free is Transana qualitative analysis software for video and audio data.
optical character recognition
The process of scanning printed type and converting it into editable text on a computer, e.g. converting a photograph of the word "cat" into the letters C, A and T stored in a data file.
The range of tones that can be captured by a device. Optical density is measured on a scale of 0 for white to 4 for black.
Using services provided by external organisations.
The set of colours assigned to a colour look-up table, thus the range of possible colours the image can have.
A sideways change in where the video camera is pointing as opposed to a tilt. Note that the camera doesn't change position but only the direction in which it points. See also tracking, dolly and crab.
Portable Document Format, an open file format developed by Adobe which is independent of the parent program. There are a range of programs available to open these documents some of which are also open source.
A technique used to analyse the way that we perceive sensory input, which can then be used to make decisions about which parts of an image, or of an audio or video signal can be removed with least subjective degradation. Used in MP3 and AAC audio compression.
Many microphones - usually condensers - require a small power source, needed either to polarize the capsule or to amplify the signal internally. This is often achieved by using an internal battery. If your microphone needs a battery always carry a spare.
Alternatively, a method was developed for delivering power through the microphone's audio cable which does not interfere in any way with the audio signal itself, hence it's name "phantom power". This 48V supply will meet the power needs of most professional and semi-professional microphones, and is provided by the microphone pre-amplifier. There will usually be a "48V" button on each channel, or a single global switch for a set of channels or the entire mixing console.
Phantom power does not affect the audio signal, and is ignored by microphones which do not require it. Only vintage ribbon microphones (very rarely encountered) are liable to damage by phantom power.
Substrate coated with emulsion containing light sensitive silver halide grains.
Compact Disk type storage technology developed by Kodak in the early 1990s.
Image editing computer application program widely used in imaging. Published by Adobe, it is generally regarded as the industry standard.
Picture element, smallest element of a digital image.
When an image is displayed at a normal viewing magnification and the pixels are apparent it is said to be pixelated.
A thin mesh or gauze shield, which can be placed a couple of inches in front of the microphone head to eliminate ‘popping' noise caused by plosives (‘b' and ‘p') in close-up vocal recording. These have a negligible effect on audio quality and are not required when speaker is more than 12-18” away.
See master archive.
Descriptive of equipment which is used for low-end professional work as well as the high-end consumer market.
A type of perceptual modelling specifically concerned with audio perception.
Personal video recorder. The term usually refers to devices used for recording TV in a digital format. These boxes may record to DVD, hard disk or both.
See quality assurance.
A system which provides confidence that the service will fulfil users' expectations.
Monitoring of systems and processes to ensure that quality of work is within defined tolerances.
quarter screen image
An image occupying one quarter of the area of a Web page.
A native file format offered by some of the more advanced digital cameras. While this format is proprietary it also offers higher quality than the standard TIFF and JPEG formats. Adobe is developing an open source format, DNG, which will retain all the data stored in the original proprietary RAW image while making the file more widely supported.
The Resource Discovery Network is an internet resource for further and higher education.
This is a common problem when using a camera mounted flash under low ambient lighting. The bright flash passes through the dilated pupils and iluminates the tissue at the back of the eye which glows red.
Transferring digital data to new storage media to avoid the effects of media deterioration. Also refers to the redrawing of the image on a CRT screen or the updating of information on a shared resource such as a database.
The encoding of a dynamically-applied effect into an audio, video or still image file to create a new file which incorporates that effect. The effect is generally something which is applied and observed in an editing program, e.g. a dissolve in a video editing program, an EQ setting in an audio editing program, or a change in gamma in a still image editing program. By rendering the image we combine it with the effect, allowing it to be exported from the editing program and observed independent of it. Note that rendering is not a reversible process; in editing programs this is not a limitation as the user can continue to use the unrendered components and make changes. However, once the rendered file is exported from the program the changes are permanent.
Changing the resolution of an image by increasing or decreasing the number of pixels. In the audio sphere, changing the highest recordable frequency of an audio recording by increasing or decreasing the sample rate.
residual current device
Residual current device,a device which cuts power to an electrical lead when an abnormal circuit is detected. While RCDs are similar to circuit breakers they perform a different function. Specifically, RCDs will shut off power when a person is about to be electrocuted, minimising the shock they get. They should be considered an essential part of a lighting kit and the presence of circuit breakers does not eliminate the need for them.
See resampling (of an image).
Spatial resolution is normally expressed as the number of pixels per linear unit e.g. 300ppi (pixels per inch), sometimes dpi (dots per inch) or spi (samples per inch). For colour resolution see bit depth.
A multi-channel uncompressed PCM audio format, defined by the European Broadcasters Union ( EBU), and an open standard. Up to 18 channels of surround audio + stereo mixdown channels and ability to incorporate additional non-PCM audio streams (e.g. MP3 or AAC). The 'raw' audio data portion of a Multi-channel Broadcast Wave file ( MBWF)
Red, green and blue, the three colours of light which can be mixed to make all other colours. Also a colour system (i.e. a way of encoding colour into a video signal) in which the colour information is broken down into red, green and blue components. See also YUV and YIQ.
A type of analogue video signal format. S-video carries picture only and is a slightly higher quality signal than composite. It normally uses 4-pin mini-DIN connectors. See also component, IEEE 1394 and USB.
All digital media, being composed of discrete elements, are produced through some sort of sampling. In the case of audio the samples are measures of the intensity of a sound at a moment in time. In the case of still images the samples are measures of the red, green and blue components of light falling on an array of discrete sensors. Video in a sense combines the two, measuring light values at siecific moments in time. By using these samples we are able to construct a replica of the original spound or image.
In digital audio, the sampling rate refers to how often the sound level is measured when making a digital recording. CD audio has a sampling rate of 44.1 KHz (44,100 times per second), and many digital audio systems sample at 48 KHz or 96 KHz. See Nyquist sampling theorem.
The maximum dimensions of the area on a flatbed scanner in which an original can be placed and digitised.
A device which delivers a digital image of that which is placed in it.
scanning area array
scanning linear array
Another way in which the detector within a digital camera can be arranged. The scanning linear array consists of one row each of red, green and blue detectors which travel across the image area. normally requires continuous (i.e. non-flash) lighting but gives high resolution images. See also area array and scanning area array.
A description of the structure given to a set of metadata elements.
A controlled vocabulary or authority list.
Small Computer Serial Interface. A system of connecting a chain of computer peripherals to a computer.
Standard-definition video is generally agreed to be video of not more than 576 lines interlaced with a refresh rate of not more than 30 frames per second. This definition is necessarily imprecise, particularly as some countries have a classification between standard- and high-definition vide called enhanced definition. See also HD.
search and retrieval
Action taken by database software after a request for an image has been submitted.
A securely backed-up copy of an original master archive file. See master archive.
The Special Educational Needs and Disability Act.
metadata schema for describing photographic collections. See
A software method of increasing the definition of edges in an image by increasing the contrast of the image. There is a trade-off when performing sharpening: as the image sharpness is increased, the subtleties of gradation between the darkest and lightest elements of the image are reduced. the result is a more "contrasty" picture.
An elastic suspension mount (aka shockmount or spider-mount) helps isolate the microphone from physical vibration and floor-borne noise (footsteps etc) - especially useful if the stand is placed on a suspended floor. Some generic shockmounts are available, but most professional microphones will be matched to a specific model, or have one bundled with the microphone.
The delay between pressing the shutter button of a camera and the taking of the photograph. This is common in budget digital cameras.
Signal-to noise ratio
All electronic audio equipment will have an element of background noise, no matter how small. In the case of microphones, signal-to-noise is particularly important, due to the need to amplify the very weak initial signal of the microphone by a large factor. In the process of amplification, all background noise will be made louder along with the signal. A higher signal-to-noises ratio (measured in decibels) is therefore desirable.
Single Lens Reflex or SLR
Single lens reflex cameras use a moving mirror which directs light from the lens to an optical eyepiece. This provides a bright image helps in composition and focussing. Most SLR cameras can accept interchangeable lenses which allow the camera to be used for a wide range of applications.
Describes the finest detail visible to the human eye. See visually lossless compression.
A candidate for becoming a standard.
A technology, format or method ratified by a respected authority.
Some stereo techniques - most notably X-Y pair or Blumlein pair - use a pair of microphones side by side. Special bars are available to allow two mics to be mounted in this way on a single heavy-duty stand or ceiling mount.
sticky shed syndrome
A problem that affects some magnetic tape sound and moving image recordings, particularly ones made in the 70s. Sticky shed syndrome occurs when the binder that holds magnetic particles to the base tape deteriorates. The binder becomes sticky and easily torn off the base tape, most often in a reel of tape by sticking to the next layer of tape in. This results in irreparable gaps in the recording. The most widely used treatment for this problem is the baking of tapes in an oven to dry the binder out. More information from the Library of Congress Preservation Directorate.
Delivering video or sound over a network in a way that allows users to watch or listen to it as it is streamed (as opposed to having to download the file and play it locally). Streaming files are often intended not to be downloadable, to prevent unlicensed copying.
See chroma subsampling.
A colour system based on reflected light. Colour CMYK printing is based on the subtractive colour system.
A colour look-up table containing information on a limited number of colours, normally 256. Computer manufacturers' system palettes may differ.
A storage medium consisting of a plastic ribbon coated with magnetic particles. Used in audio and video recording as well as for the storage of computer data. Note that the medium is distinct from the method of encoding the data: tape may be used for both analogue and digital recording, although tapes of the same physical size that are used for digital and analogue should not be mixed. While largely superseded by other media such as CD, DVD, hard disk and various solid state devices, tape is still widely used due to its low cost, the installed equipment base and its suitability for short-term archiving.
Technical Advisory Service for Images, the former name of JISC Digital Media.
A controlled vocabulary, structured into a hierarchy and presenting semantic relationships.
Small, low resolution preview, often hyperlinked to a high resolution version of the same image.
Tagged Image File Format, a widely used file format particularly suited to the storage of high quality archive images.
An up and down change in where the video camera is pointing as opposed to a pan. Note that the camera doesn't change position but only the direction in which it points. See also tracking, dolly and crab.
A tilt-shift lens allows the photographer to make corrections to image perspective. With the shift movement the lens is moved up/down left/right while remaining parralel with the sensor. This is mainly used to correct converging verticals or horizontals. The tilt movement allows the lens to be rotated or tilted in relation to the sensor, this allows the photographer to adjust the plane of focus and take greater control over depth of field.
Recording a broadcast so that it can be viewed or listened to at another time. This should not be confused with iPlayer and other video streaming technologies, recordings from which are not permitted under the ERA and ERA+ licences. See Intellectual Property Office for more information.
Tracking error refers to any problems in the retrieval of stored information due to the physical alignment of the recording or playback device. It is most noticeably encountered with analogue videotape recorders.
An audio or video tape-based recorder stores picture and/or sound information on the tape by magnetising a path of particles on the tape as it is pulled under the record head. The exact location of this path on the tape is determined by the physical position of the record head with respect to the tape. If, when the recording is played back, the playback head is not located in the exact same position as the record head was when the recording was made, the picture and/or sound recreated from the information on the tape will be compromised. This is tracking error. It is most easily apparent on VHS video recordings, where it is indicated by a band of 'snow' or 'static' running horizontally across the screen or at the top or bottom edge. All analogue video decks have either manual tracking controls or automatic tracking correction to eliminate this problem.
On analogue audio decks, tracking error is not as much of a problem due to the smaller amount of information being put onto the tape. Nonetheless, tape head alignment is a normal part of an audio deck's regular servicing.
Due to the nature of digital recording and storage, digital tracking error doesn't appear as a degradation in information but rather as a complete and catastrophic failure. As such, it can be mistaken for other data retrieval problems.
transparent media adaptor
The part of a flatbed scanner used to scan transparent media. Usually an optional extra.
true colour image
A 24 bit image.
Video format developed in the late 1960s and early 1970s. Originally developed for professional use with advanced editing features, U-matic was one of the first to use a video cassette system instead of the prevalent open reel. As such it was a precursor to home video formats VHS and Betamax.
A digital image, video or sound file which has not been subject to compression.
Uniform resource locator, the address of a Web page or other Web resource.
Universal Serial Bus, a standard connection between computers and peripherals such as mice, keyboards, printers, hard discs and scanners. USB is also used as an interface for transferring video from consumer camcorders. It carries both picture and sound. See also composite, S-video, component and IEEE 1394.
A system set into place that will confirm a registered user is who they say they are.
The way in which the user interacts with a device or piece of software.
The procedure where a user must submit information to a form before being granted permission to enter a system.
An image that is composed of individual elements e.g. arc, line, polygon, that have their own attributes. These attributes can be individually edited. A drawing type package is usually required to display such images. See also raster image and our Vector Graphics Illustrated Glossary.
Video Home System (originally Vertical Helical Scan). Magnetic video recording format and de facto home video recording standard developed by JVC. VHS was the winner over Betamax in the home video recording format war of the late 1970s and early 1980s.
video enabled SLR
A stills SLR camera which can also capture video clips. As SLR cameras use larger sensors than the typical camcorder video enabled SLRs can shoot film with a very shallow depth of field.
See metadata schema.
A problem that affects acetate-based film. As it starts to degrade, the film releases acetic acid which gives off a vinegar odour. Such decay can make the film unusable, but research has shown that vinegar syndrome can be delayed by proper storage. See our advice document on Analogue Film Types Used for Still and Moving Images.
visually lossless compression
A subjective term referring to a lossy compression technique that reduces the file size by removing information of fine enough detail that the eye does not notice. A visual comparison between the original file and the compressed file does not show any differences but a comparison of the binary file will.
A software system that provides online tools to support teaching and learning
Microsoft Wave Audio Format. The native audio file format of Windows operating system - also compatible with all other OS and most media devices. Uncompressed PCM audio format with a range of potential sampling rates and bit depth.
A very rapid pan, so fast that the image becomes a blur, whip pans are sometimes used to provide the editor with a point at which to cut to another scene.
An adjustment made by a capture device to correct for any colour bias due to the colour temperature of the light source.
wide angle lens
A lens that captures a larger field of view than a normal or standard lens. For full frame digital SLRs a standard lens is 50mm, any lens with a shorter focal length is normally referred to as wide-angle.
A hairy cover (sometimes called a ‘dead cat') will reduce the effects of wind noise in an outdoor location.
World Wide Web, the Internet.
Another name for S-video.
A colour system (i.e. a way of encoding colour into a video signal) in which the colour information is broken down into a luminance component (Y) and two chrominance components (I and Q), YIQ is used in the NTSC television system. See also RGB and YUV.
A colour system (i.e. a way of encoding colour into a video signal) in which the colour information is broken down into a luminance component (Y) and two chrominance components (U and V), YUV is used in the PAL television system. See also RGB and YIQ.
A protocol that is an international standard for information retrieval.
A technique used to examine a portion of an image in greater detail. The term zoom originally referred to lenses with variable focal length. A zoom lens allowed the photographer to change the focal length they were using without changing the lens. The development of faster zoom lenses resulted into their introduction into cinematography. Because the focal length could be changed while a shot was being taken the term became a verb as well as a noun: in a movie the camera could zoom into or out of a scene. It is important to recognise that zooming in does not change perspective, but rather magnifies the image. Thus the feature on much word processing and image manipulation software that allows the user to magnify a part of the viewing window is referred to as a zoom. In the digital domain it should be recognised that zooming in on a raster image results in a lower-resolution picture, since the pixels are simply being enlarged: this is why the digital zoom on cameras and camcorders gives poor results. By contrast, a zoom in on a vector image should maintain the same resolution.