builddate=Sat Mar 3 13:36:27 2007n char-precedence= description=Personal technical glossary of terms relating to vision sciences including stereoscopy, video coding, algorithms, geometry and standards. dict-size=91672 id=Image, Video Processing and Computer Vision index=02DFSn00eigengraun328510parallax barriern65741 items=491 maintainer=Lyndon Hill max-entry-length=649 max-word-length=33 search-ignore-chars=-. 2DFS {s} {ct}video proc.{/ct} {ss}Two Dimensional Full Search. A block matching algorithm (see {sa}BMA{/sa}) for {sa}motion estimation{/sa}. 2DFS, also known as exhaustive block matching, will always find the optimal result therefore all BMA search strategies must compare against 2DFS.{/ss} {/s}a posteriori {s} {ct}math.{/ct} {ss}Posterior probability, calculated based on the observed frequency.{/ss} {/s}a priori {s} {ct}math.{/ct} {ss}Prior probability, assigned in advance based on any empirical evidence.{/ss} {/s}aberration {s} {ct}optics{/ct} {ss}The failure of an optical lens to produce an exact point-to-point correspondence between the object and its resulting image. Various types are chromatic, spherical, coma, astigmatism and distortion.{/ss} {/s}absorption {s} {ct}optics{/ct} {ss}The loss of light of certain wavelengths as it passes through a material and is converted to heat or other forms of energy.{/ss} {/s}absorption spectrum {s} {ct}optics{/ct} {ss}The relationship between the wavelength of light striking a pigment and how strongly the light is absorbed.{/ss} {/s}accidental view {s} {ss}A special view of an object in which small perturbations in lighting or viewing direction drastically change its appearance. For example, imagine looking at a pencil straight on from the tip. (As opposed to {sa}generic view{/sa}).{/ss} {/s}accommodation {s} {ct}HVS{/ct} {ss}Adjustment of eye focus for near and far objects.{/ss} {ss}Adjustment of the optics of an eye to keep an object in focus on the retina as its distance from the eye varies. Process of adjusting the focal length of a lens.{/ss} {/s}achromatopsia {s} {ss}A loss of colour vision unaccompanied by attendant loss of other perceptual functions.{/ss} {/s}action potential {s} {ss}Action spectra.{/ss} {ss}A photoreceptor's relative spectral sensitivity.{/ss} {/s}active illumination {s} {ct}image proc.{/ct} {ss}Lighting a scene with a light source coordinated with the acquisition of an image. Strobed flash tubes, pulsed lasers and scanned LIDAR beams are examples.{/ss} {/s}acuity {s} {ss}The highest spatial frequency resolvable with a grating of unity contrast (i.e. the maximum possibly contrast).{/ss} {/s}AdaBoost {s} {ct}comp. vis.{/ct} {ss}AdaBoost (adaptive boosting) is a classification algorithm aimed at producing a very accurate prediction rule by combining rough and moderately inaccurate "rules of thumb." AdaBoost is adaptive in the sense that subsequent classifiers built are tweaked in favour of those instances misclassified by previous classifiers.{/ss} {/s}adaptation {s} {ss}A change in the sensitivity to light of a photoreceptor or the visual system as a whole to match the average light intensity present.{/ss} {/s}afferent {s} {ss}Heading towards. A system's afferent signals are those entering the system from elsewhere. (As opposed to {sa}efferent{/sa}).{/ss} {/s}aftereffect {s} {ct}biol.{/ct} {ss}afterimage{/ss} {ss}A long lasting change in perceived brightness that occurs after prolonged viewing of a given luminance that remains after the luminance has been changed. Presumably due to adaptation in the exposed region.{/ss} {/s}AIC {s} {ct}alg.{/ct} {ss}Akaike's Information Criterion. Akaike wanted it to be known by the letter "A" as he expected there to be a series of criteria, B Information Criterion, etc.{/ss} {/s}albedo {s} {ct}optics{/ct} {ss}The fraction of light reflected by a surface.{/ss} {/s}aliasing {s} {ct}sig. proc.{/ct} {ss}Results when density of sampling is less than density of signal. One can only measure the portion of the input falling over the sampled positions. Sampled values for two different signals can be the same when the in-between values are different.{/ss} {/s}allelotropia {s} {ss}A depth percept can cause a shift in perceived form, namely change in the perceived distance between patterns in a configuration. For example that a pattern AB C is viewed in one eye and the pattern A BC is viewed through the other, the letter B is seen in depth at a position halfway between A and C.{/ss} {/s}amacrine cell {s} {ct}biol.{/ct} {ss}A type of neuron seen in the retina.{/ss} {/s}ambient light {s} {ct}comp. vis.{/ct} {ss}Light which is present in the environment of the imaging front end of a vision system and generated from outside sources. This light, unless used for actual scene illumination, will be treated as background noise by the vision system.{/ss} {/s}ambient vision {s} {ct}biol.{/ct} {ss}The role of vision involved in orienting an animal in space and guiding its larger movements. Sensitive to motion and dependent on peripheral vision. (As opposed to {sa}focal vision{/sa}).{/ss} {/s}amblyopia {s} {ct}biol.{/ct} {ss}An abnormal development of spatial vision associated with anisometropia or strabismus in early life. Visual acuity is reduced in the defocused or deviated eye as a result.{/ss} {/s}ametropia {s} {ct}biol.{/ct} {ss}An abnormal refractive condition of the eye in which images fail to focus on the retina.{/ss} {/s}amodal {s} {ss}Perceptually present, but not having a real phenomenological presence. (As opposed to {sa}modal{/sa}). {/ss} {/s}amodal completion {s} {ss}The creation of a subjective contour that is without local sensory attributes e.g. contrast difference. It is neither a cognitive inference nor a projection but a direct perception. Seen most often in displays that have partially occluded objects. (See also {sa}modal completion{/sa}).{/ss} {/s}anaglyph {s} {ct}3D{/ct} {ss}Device for creating 3D images using red and blue filters for the two eyes.{/ss} {ss}3D image formed using glasses with different lens colours or polarisation.{/ss} {/s}anchoring {s} {ss}In any scene, the object which is the lightest is perceived as being white, or is 'anchored' to white.{/ss} {/s}angle of incidence {s} {ct}optics{/ct} {ss}Angle between an incident ray of light and the perpendicular to a surface.{/ss} {/s}angle of reflection {s} {ct}optics{/ct} {ss}Angle between a reflected ray of light and the perpendicular reflecting surface.{/ss} {/s}angle of refraction {s} {ct}optics{/ct} {ss}Angle between a refracted ray of light and the perpendicular to the refracting surface.{/ss} {/s}anisometropia {s} {ss}A disorder involving unequal refractive errors in the two eyes.{/ss} {/s}anisotropic {s} {ss}Any process or filter which is directionally selective or biased. (As opposed to {sa}isotropic{/sa}).{/ss} {/s}anisotropy {s} {ct}geom.{/ct} {ss}Having unequal scale in orthogonal directions{/ss} {/s}aperture problem {s} {ct}video proc.{/ct} {ss}Any motion detecting device with a field of view which is small relative to an edge moving through it can only detect the component of velocity at right angles to the edge, while the component parallel to the edge is invisible.{/ss} {/s}apparent motion {s} {ss}A observer presented with a display in which two items (lines, dots) in different locations are alternately exposed at certain interstimulus intervals will report seeing the item move from the first position to the second position. Illusion depends on the spatial separation, luminance and duration of the items.{/ss} {/s}area array camera {s} {ct}hw.{/ct} {ss}A solid state imaging device with both rows and columns of pixels, forming an array which produces a 2D image.{/ss} {/s}area contrast {s} {ss}A contrast effect which is not limited to the borders of an enclosed region. The change of brightness produced by contrast at the edges of the region spreads uniformly over the entire enclosed region.{/ss} {/s}array processor {s} {ct}hw.{/ct} {ss}A specially designed vision engine peripheral which attaches to the host to speed up arithmetical calculations by using parallel processing techniques. The host manages image data access and analysis results.{/ss} {/s}assimilation {s} {ss}A neutral pattern of intermediate luminance appears brighter if a superimposed pattern is made of high luminance lines, yet darker if the pattern consists of low luminance lines. This effect is in the opposite direction as is seen in simultaneous contrast.{/ss} {/s}AST {s} {ct}geom.{/ct} {ss}Arbitrary Shape Transform. Many transforms such as {sa}DCT{/sa} work over a rectangular area. An AST does not have this constraint.{/ss} {/s}astigmatism {s} {ct}optics{/ct} {ss}A defect in a lens which causes blur or imperfect image results, since the rays from a given point fail to meet at the focal point.{/ss} {/s}autofocus {s} {ct}hw.{/ct} {ss}The ability of an imaging system to control the focus of the lens to obtain the sharpest image on the detector. Edge crispness is a typical control variable.{/ss} {/s}automatic gain control {s} {ct}hw.{/ct} {ss}A fast gain control that aims to achieve a constant output by changing gain in proportion to signal strength.{/ss} {/s}autostereogram {s} {ct}3D{/ct} {ss}Unlike classical Random Dot Stereograms which require two separate images presented dichoptically, an autostereogram consists of just one image viewed by two eyes simultaneously. A depth percept is attained from this image.{/ss} {/s}autostereoscopic display {s} {ct}3D, hw.{/ct} {ss}A type of 3D display where additional viewing apparatus such as special glasses are not required.{/ss} {/s}background {s} {ss}The part of a scene behind the object to be imaged.{/ss} {/s}backlighting {s} {ss}Placement of a light source behind an object so that a silhouette of that object is formed. It is used where outline information of the object and its features is important rather than surface features.{/ss} {/s}backpropagation {s} {ct}alg.{/ct} {ss}A training technique which adjusts the weights of the hidden and input layers of a neural net to force the correct decision for a given feature vector data input set.{/ss} {/s}baffle {s} {ct}optics{/ct} {ss}A type of shield that prohibits light from entering an optical system.{/ss} {/s}bandwidth {s} {ct}sig. proc.{/ct} {ss}The ratio of the spatial frequencies at which half the maximum contrast sensitivity is obtained.{/ss} {/s}barber pole illusion {s} {ct}HVS{/ct} {ss}The direction of motion of a diagonal grating pattern drifting behind a rectangular aperture depends upon the elongation of the aperture. The prevailing explanation is that the perceived direction of motion results from the integration of motion signals from grating terminators at the edges of the aperture. As a vertically elongated aperture has larger number of terminators with vertical trajectories, vertical motion prevails.{/ss} {/s}barrel distortion {s} {ct}optics, image proc.{/ct} {ss}An optical imperfection which causes an image to bulge convexly on all sides similar to a barrel. {/ss} {/s}BDM {s} {ct}vid. proc.{/ct} {ss}Block Distortion Metric. Used for motion estimation, metrics include MSE, SSE, MAD, SAD, etc.{/ss} {/s}beamsplitter {s} {ct}optics{/ct} {ss}An optical device which divides one beam into two or more separate beams. A simple coated piece of glass in the optical path might reflect 60% of the light down onto the object, while allowing the other 40% to pass.{/ss} {/s}Benussi ring illusion {s} {ss}See {sa}Koffka-Benussi ring illusion{/sa}.{/ss} {/s}binding problem {s} {ss}If colour, form, and motion are processed in separate areas of the brain, how/where is this information reassembled to create a single unified percept? (e.g. a purple box moving to the left).{/ss} {/s}binocular disparity {s} {ct}3D{/ct} {ss}The difference in position of two retinal images of an object that do not fall on exactly corresponding retinal positions.{/ss} {/s}binocular field {s} {ct}3D{/ct} {ss}A receptive field which responds to a cells optimal stimulus if it is presented to either eye.{/ss} {/s}binocular overlap {s} {ct}3D{/ct} {ss}The segment of the optic array sampled by both eyes.{/ss} {/s}binocular rivalry {s} {ct}3D{/ct} {ss}Occurs when the two eyes are presented with different stimuli. Instead of seeing a summation of the two images, our perception switches from one image to the other.{/ss} {/s}binocular vision {s} {ct}3D{/ct} {ss}Vision performed with two eyes/sensors whose outputs are often used to extract relative stereoscopic depth.{/ss} {/s}binocular zone {s} {ct}3D{/ct} {ss}The central region of the visual field from which light enter both eyes. (See also {sa}monocular zone{/sa}).{/ss} {/s}binoptic stimulation {s} {ct}3D{/ct} {ss}When the same image is presented to each eye. (See also {sa}dichoptic stimulation{/sa} and {sa}monoptic stimulation{/sa}).{/ss} {/s}birefringence {s} {ct}optics{/ct} {ss}Change of refractive index with respect to orientation and polarisation of light into a transparent material.{/ss} {/s}blanking (period) {s} {ct}TV{/ct} {ss}The time during a raster scan retrace when the video signal is suppressed.{/ss} {/s}bleaching {s} {ct}biol.{/ct} {ss}Photoreceptors, most notably rods, can be driven to saturation by bright visual stimuli and become insensitive to light changes in this region, then they are said to be 'bleached'.{/ss} {/s}blind spot {s} {ct}biol.{/ct} {ss}The location where optic nerve fibres leave the retina. This area has no photoreceptors and therefore no visual input. The cortex appears to fill in this missing information so we are not conscious of the blind spot.{/ss} {/s}blindsight {s} {ss}A phenomenon reported in individuals suffering from cortical blindness (i.e. damage to the primary visual cortex resulting in blindness). Individuals with blindsight report that they are unable to see, yet under forced choice conditions are able to indicate the presence and location of visually presented objects.{/ss} {/s}block artefacts {s} {ct}image proc., video proc.{/ct} {ss}Visual artefacts created when an image is compressed with an algorithm using block coding is reconstructed. (See also {sa}block coding{/sa}).{/ss} {/s}block coding {s} {ct}video proc., image proc.{/ct} {ss}Any image representation that subdivide the image into blocks. (See also {sa}block artefacts{/sa}).{/ss} {/s}block distortion metric {s} {ss}See {sa}BDM{/sa}.{/ss} {/s}BMA {s} {ct}video proc.{/ct} {ss}Block Matching Algorithm. Used for motion estimation.{/ss} {/s}border contrast {s} {ss}A localised contrast effect which is limited to the border immediately adjacent to the contrast discontinuity. (As opposed to {sa}area contrast{/sa}).{/ss} {/s}Brewster's angle {s} {ct}optics{/ct} {ss}The angle at which incident light, by reflecting at a boundary between two mediums of different refractive indices (ie air/glass or air/water), becomes plane polarised. For air/glass it is about 67.4 degrees.{/ss} {/s}brightness {s} {ct}optics{/ct} {ss}The total amount of light or incident illumination on a scene or object per unit area. Also called intensity.{/ss} {/s}brightness constancy {s} {ss}The perceived brightness of real objects in a natural environment is largely independent of changes in the overall illumination.{/ss} {ss}Often mistakenly used for lightness contrast. However there is evidence that luminescent objects can be perceived to be of the same luminance despite changes in ambient illumination or background.{/ss} {/s}Brow-Sulzer effect {s} {ss}An enhancement of brightness/darkness perception is found in the time domain. Stimuli of short duration evoke stronger sensations than stimuli of long duration.{/ss} {/s}bush hogging {s} {ct}image proc.{/ct} {ss}Perceptually thresholding low energy pixels.{/ss} {/s}cafe wall illusion {s} {ct}HVS{/ct} {ss}Although the lines composing the image are parallel, they do not appear to be.{/ss} {/s}camera calibration {s} {ct}comp. vis.{/ct} {ss}Process to determine the configuration of 2 cameras, given images taken with the cameras overlapping the field of view. Results in a {sa}fundamental matrix{/sa}.{/ss} {/s}campro {s} {ct}comp. vis.{/ct} {ss}Camera-Projector. A system where a camera is used to capture information about the scene so that images can be preprocessed before being projected. See also {sa}procam{/sa}.{/ss} {/s}canonical viewpoint {s} {ss}A particular viewpoint of an object that people are more likely to imagine, quicker to name and more likely to classify as the best view of an object. Suggests that object representation may not be viewpoint independent.{/ss} {/s}cardboard effect {s} {ct}3D{/ct} {ss}A phenomenon when 3D objects set at different depths appear flat to the viewer, as if made from paper; i.e. each object has only one depth rather than a detailed surface.{/ss} {/s}catadioptric {s} {ct}optics{/ct} {ss}Belonging to, produced by, or involving both the reflection and the refraction of light.{/ss} {/s}CATV {s} {ct}TV{/ct} {ss}Community Area Television. Another name for cable TV.{/ss} {/s}CCD {s} {ct}hw.{/ct} {ss}Charge Coupled Device. A photo-sensitive image sensor implemented with large scale integration technology.{/ss} {/s}centroid {s} {ct}geom.{/ct} {ss}Points that are, respectively, the centre of a given area or midpoint of a given line segment.{/ss} {/s}CFF {s} {ss}See {sa}critical flicker frequency{/sa}.{/ss} {/s}cheirality {s} {ct}geom., comp. vis.{/ct} {ss}Property of a point that specifies if it lies in front of or behind the camera.{/ss} {/s}chroma {s} {ct}image proc.{/ct} {ss}The quality of a colour including both the hue and saturation. Not present in grey.{/ss} {/s}chromostereopsis {s} {ct}3D, HVS{/ct} {ss}Use of colour can give a feeling of depth: for some people reds advance and blues recede but this is not universal.{/ss} {ss}The optics of the eye are such that short wavelengths are refracted slightly more than long wavelengths creating a positional disparity on the retina. When viewed by two eyes a stereoscopic disparity is obtained. This is termed chromostereopsis or chromatic stereopsis.{/ss} {/s}CID {s} {ct}hw.{/ct} {ss}Charge Injection Device - A photo-sensitive image sensor implemented with large scale integration technology. Based on charge injection technology, a CID can be randomly addressed, non-destructively read, can be subscanned in a small region and is less susceptible to charge overflow from bright pixels to neighbours. The pixel structure is contiguous with maximum surface to capture incident light which is useful for sub-pixel measurement.{/ss} {/s}CIE {s} {ct}image proc.{/ct} {ss}An acronym for a chromaticity coordinate system developed by the Commission Internationale de l'Eclairage, the international commission on illumination. In the CIE system, a plot of ratios (x, y and z) of the three standard primary colours (tristimulus values) to their sum. The most common diagram is the 2 dimensional CIE (x,y).{/ss} {/s}classification {s} {ct}comp. vis.{/ct} {ss}Assignment of image objects to one of two or more possible groups. Decisions are made by evaluating features either 1) structurally based on relationships or 2) statistically. For example, 1) a penny is round, a certain diameter (+/- a tolerance) and has a histogram of a mean value; or 2) statistically, the object is measured a number of times, then the average and standard deviation are recorded. After training the features are weighted based on significance in object identification. For multiple features, absolute values are used.{/ss} {/s}clique {s} {ct}alg.{/ct} {ss}A subset of sites in which every pair of distinct sites are neighbours.{/ss} {/s}closing {s} {ct}image proc.{/ct} {ss}A dilation followed by an erosion. A morphological operator useful to close holes and boundaries.{/ss} {/s}coaxial illumination {s} {ct}optics{/ct} {ss}Front lighting with the illumination path running along the imaging optical axis and usually introduced with a 45 degree angle beam splitter.{/ss} {/s}coherent fibre optics {s} {ss}A bundle of optical fibres with the input and output spatial x-y relationship maintained, resulting in near spatially correct image transmission.{/ss} {/s}colinear {s} {ct}geom.{/ct} {ss}When two points are on the same line.{/ss} {/s}colinearity {s} {ct}geom.{/ct} {ss}A straight line is imaged as a straight line, in projective geometry.{/ss} {/s}collimate {s} {ct}optics{/ct} {ss}To produce light with parallel rays.{/ss} {/s}collimated lighting {s} {ct}optics{/ct} {ss}Radiation from a given point with every light ray considered parallel. In actuality, even light from a very distant point source (i.e. a star) diverges somewhat. Note that all collimators have some aberrations.{/ss} {/s}colour {s} {ss}A visual object attribute which may be described by a "coordinate system" such as hue, saturation and intensity (HSI), CIE or LAB. Wavelengths in the visible part of the electromagnetic spectrum to which retinal rods respond.{/ss} {/s}colour constancy {s} {ss}Despite changes in wavelength (such as at sunset, or on cloudy days) objects are perceived to maintain their surface colour.{/ss} {/s}colour opponency {s} {ct}biol.{/ct} {ss}When a cell is excited by one part of the visible spectrum and inhibited by another. First observed in ganglion cells in the retina.{/ss} {/s}colour space {s} {ss}A two or three dimensional space used to represent an absolute colour coordinate. RGB, HSI, LAB and CIE are all representations of colour spaces.{/ss} {ss}A mathematical construct that allows us to visually denote the mixture of different colours.{/ss} {/s}colour temperature {s} {ss}A colourimetric concept related to the apparent visual colour of a source, but not its actual temperature.{/ss} {/s}colourimetry {s} {ss}Techniques used to measure colour of an object or region and to define the results in a comparison or coordinate system.{/ss} {/s}composite video {s} {ct}TV{/ct} {ss}A television signal which is produced by combining both a video or picture signal with horizontal and vertical sync and blanking signals.{/ss} {/s}condensation {s} {ct}comp. vis.{/ct} {ss}A probability based tracking algorithm, the name derives from Conditional Density Propagation.{/ss} {/s}condenser lens {s} {ct}optics{/ct} {ss}Used to collect and redirect light for the purpose of illumination. Often used to collect light from a small source and project even light onto an object.{/ss} {/s}cone {s} {ct}biol.{/ct} {ss}Photoreceptor for day vision. Higher acuity and temporal resolution than rods. Mediates colour vision. Highly concentrated in fovea. Graded responses (no action potential). There are three classes of cones, short, medium and long wavelength cones.{/ss} {/s}cone opsin {s} {ct}biol.{/ct} {ss}Light absorbing molecule in cone cells.{/ss} {/s}conformal structure {s} {ss}A natural geometric structure on surfaces, which governs many physics phenomena, such as heat diffusion, electromagnetic fields, etc.{/ss} {/s}contrast {s} {ss}The difference of light intensity between two adjacent regions in the image of an object. Often expressed as the difference between the lightest and darkest portion of an image. Contrast between a flaw or feature and its background is the goal of illumination.{/ss} {ss}The ratio between the maximum and minimum intensities in a light pattern.{/ss} {/s}contrast enhancement {s} {ct}image proc.{/ct} {ss}Stretching of the grey level values between dark and light portions of an image to improve both visibility and feature detection.{/ss} {/s}contrast sensitivity function {s} {ss}The reciprocal of the threshold contrast required to obtain a criterion response from a cell or a human subject as a function of spatial frequency. Falls off in sensitivity as the spatial frequency of the test pattern increases. (See also {sa}modulation transfer function{/sa}){/ss} {/s}corona affect {s} {ct}video proc.{/ct} {ss}Artefact where non-zero motion vectors affect a stationary background.{/ss} {/s}correspondence problem {s} {ct}3D{/ct} {ss}In stereopsis the challenge of matching elements in one eye with elements in another eye. Also known as the matching problem.{/ss} {/s}corridor illusion {s} {ss}The cylinders of equal size in a picture are perceived to be of different sizes when they lie in distinct positions within a rectangular grid whose spatial scale diminishes toward a fixation point on the horizon which create depth perspective cues.{/ss} {/s}CPD {s} {ct}biol.{/ct} {ss}Cycles per degree of visual angle. The human limit is about 30 cpd in the fovea for an individual with 20/20 vision.{/ss} {/s}Craik-O'Brien cornsweet effect {s} {ss}Two identically luminant rectangles except for a luminance cusp near the border appear to have different luminance levels.{/ss} {/s}critical flicker frequency {s} {ss}The frequency of flicker where the alternating levels of brightness are seen as a single level. The frequency is dependent on brightness levels and retinal location.{/ss} {/s}crosstalk {s} {ct}hw.{/ct} {ss}In the case of 3D, crosstalk is where some of the left image can be seen in the right image and vice-versa. For a multiview display, crosstalk reduces the effectiveness of the 3D effect. A rule of thumb is that it should be less than 20%.{/ss} {/s}CSS image {s} {ss}Curvature Scale Space image. A multiscale organisation of inflection points of a closed planar curve.{/ss} {/s}curvature scale space {s} {ss}See {sa}CSS image{/sa}.{/ss} {/s}CV {s} {ss}Computer Vision.{/ss} {ss}Composite Video.{/ss} {/s}dark light {s} {ct}biol.{/ct} {ss}Rods spontaneously produce a signal that is indistinguishable from a photon elicited event even in complete darkness about once every 160 msec.{/ss} {/s}darkfield illumination {s} {ss}Lighting of objects, surfaces or particles at very shallow or low angles, so that light does not directly enter the optics. Objects are bright with a dark background. This grazing illumination causes specular reflections from abrupt surface irregularities.{/ss} {/s}DCT {s} {ss}See {sa}discrete cosine transform{/sa}.{/ss} {/s}DDC {s} {ct}hw.{/ct} {ss}Display Data Channel. Specified in VESA's VGA standard to allow a display to communicate to the driving electronics information about timings and resolutions. See also {sa}EDID{/sa}.{/ss} {/s}degree of convergence {s} {ss}The angle of inclination of the two eyes used in depth perception {/ss} {/s}delayed match to sample {s} {ss}Subject is shown a stimulus and then after a delay is required to choose the same stimulus from a number of stimuli to obtain reward.{/ss} {/s}depth capture {s} {ss}Objects in an image with no apparent depth information can be captured by surrounding surfaces which do contain depth information.{/ss} {/s}depth of field {s} {ct}optics{/ct} {ss}The range of an imaging system in which objects are in focus.{/ss} {/s}depth perception {s} {ct}HVS{/ct} {ss}The perception of solidity of a visual object and its location in the spatial field, through the fusion in the brain of the two slightly dissimilar images from the two eyes.{/ss} {/s}DFD {s} {ct}video proc.{/ct} {ss}Displaced Frame Difference. The error between pixels from two frames, where the relative position of one frame (or a local area of it) is displaced. Used in motion estimation.{/ss} {/s}dichoptic stimulation {s} {ct}optics{/ct} {ss}When different images are presented to each eye. (See also {sa}binoptic stimulation{/sa} and {sa}monoptic stimulation{/sa}.){/ss} {/s}dichroic filter {s} {ct}optics{/ct} {ss}A filter used to transmit light based on its wavelength, rather than on its plane of vibration. Transmits one colour, while reflecting a second when illuminated with white light. Often used in head up displays.{/ss} {/s}dichromatic colour vision {s} {ct}HVS{/ct} {ss}Colour vision based on two cone photoreceptor pigments in the retina. (See also {sa}trichromatic colour vision{/sa} and {sa}tetrachromatic colour vision{/sa}.){/ss} {/s}diffraction {s} {ct}optics{/ct} {ss}The scattering of rays of light by collision with particles of matter as they pass through a medium such as air or water, or pass by a edge or narrow aperture. Plays a role when the pupil is small.{/ss} {/s}diffuse reflection {s} {ss}Light which bounces off an object surface in many different directions. Light radiated from a matte surface is highly diffused.{/ss} {/s}diffused lighting {s} {ss}Scattered soft lighting from a wide variety of angles used to eliminate shadows and specular glints from profiled, highly reflective surfaces.{/ss} {/s}dilation {s} {ct}image proc.{/ct} {ss} A morphological operation which moves a probe or structuring element of a particular shape over the image, pixel by pixel. When an object boundary is contacted by the probe, a pixel is preserved in the output image. The effect is to "grow" the objects.{/ss} {/s}dioptre {s} {ss}A dioptre is a reciprocal metre. It is a measure of the power of a lens or optical system in bringing rays to a focus. The dioptric power of a thin lens is the reciprocal of the distance between the centre of the lens and its focal point as measured in metres.{/ss} {/s}diplopia {s} {ct}HVS{/ct} {ss}When the disparity between two images is too great, the human visual system cannot fuse the two images resulting in image doubling.{/ss} {ss}Double vision.{/ss} {/s}discounting the illuminant {s} {ss}Illumination of the visual world tens to be non-uniform, and fluctuates. in order for the visual system to create a consistent perception of colour and lightness it must somehow discount fluctuation and gradient in the lighting source.{/ss} {/s}discrete cosine transform {s} {ct}standards{/ct} {ss}An image coding technique used in JPEG.{/ss} {/s}disparity gradient {s} {ct}3D{/ct} {ss}The ratio of the difference between two feature's disparities and their cyclopean separation. Steeply slanted surfaces have large disparity gradients. Human binocular fusion will only tolerate a disparity gradient of about 1. {/ss} {/s}dispersion {s} {ss}Separation of a beam of light into its wavelength components, each of which travel at slightly different speeds. Also called chromatic dispersion.{/ss} {/s}DJVU {s} {ct}image proc.{/ct} {pr}deja vu{/pr} {ss}A standard for compressing scanned documents.{/ss} {/s}DLP {s} {ct}hw.{/ct} {ss}Digital Light Processing (using micromirrors i.e. a {sa}DMD{/sa}).{/ss} {/s}DMD {s} {ct}hw.{/ct} {ss}Digital Micromirror Device. Texas Instruments' chip with thousands of tiny mirrors, one for each pixel.{/ss} {/s}DMIF {s} {ss}Delivery Multimedia Integration Framework.{/ss} {/s}DPCM {s} {ct}sig. proc.{/ct} {ss}Differential Pulse Code Modulation.{/ss} {/s}DSM-CC {s} {ct}standards{/ct} {ss}Digital Storage Media - Command and Control.{/ss} {/s}duality principle {s} {ct}geom.{/ct} {ss}Any 2D projective geometry theorem has a corresponding dual theorem that may be derived by interchanging the roles of points and lines in the original theorem.{/ss} {/s}DVB {s} {ct}standards{/ct} {ss}Digital Video Broadcasting. Standard for digital television broadcasting. DVB-T is for terrestrial services, DVB-S is for satellite services, DVB-C is for cable services and DVB-H is for handheld receivers.{/ss} {/s}DVI {s} {ct}standards{/ct} {ss}Digital Video Interface. Standard for transmitting uncompressed RGB data, usually by a cable.{/ss} {/s}dynamic programming {s} {ct}opt.{/ct} {ss}An optimisation technique. Walk through possible solutions recording the solution state. Recognise and discard suboptimal solutions.{/ss} {/s}Ebbinghaus illusion {s} {ct}HVS{/ct} {ss}Although the two central circles are the same size the one surrounded by smaller circles usually appears larger than the one surrounded by large circles.{/ss} {/s}eccentricity {s} {ss}Angular distance of a point on the retina from the centre of the fovea.{/ss} {/s}edge detection {s} {ss}The ability to determine the edge of an object or feature in an image.{/ss} {/s}edge integration {s} {ss}Describes a model of lightness perception in which a region's lightness is computed by integrating over the contrast edges in an image.{/ss} {/s}edge operator {s} {ss}Templates for finding edges in images.{/ss} {/s}EDID {s} {ct}hw.{/ct} {ss}Extended Display Identification Data. Part of {sa}DVI{/sa} that communicates information about the display that is connected. The equivalent in VGA is {sa}DDC{/sa}.{/ss} {/s}efferent {s} {ss}Heading away. A system's efferent signals are those exiting to elsewhere. (As opposed to afferent){/ss} {/s}egomotion {s} {ct}comp. vis.{/ct} {ss}When the camera moves but the scene is stationary.{/ss} {/s}Ehrenstein illusion {s} {ct}HVS{/ct} {ss}A series of radial lines create an illusory circle that appears to be brighter than the background. {/ss} {/s}eigengrau {s} {ct}HVS{/ct} {ss}German word for 'intrinsic grey'. When both entire retinal images are stabilised, the observer does not perceive black but a non-descript grey fog.{/ss} {/s}EM {s} {ct}alg.{/ct} {ss}Expectation-Maximimisation.{/ss} {/s}emmetropia {s} {ss}An eye whose image is focused on the retina, rather than in front of behind it.{/ss} {/s}end-inhibition {s} {ss}A property of some cells in the visual cortex which respond strongly to either an edge, a bar or a slit which ends within the receptive field.{/ss} {/s}end-stopped cell {s} {ss}An orientation selective cell which is also sensitive to the end of a line or edge, responding to short but not long lines or edge stimuli.{/ss} {/s}epipolar line {s} {ct}comp. vis.{/ct} {ss}For a given point in space, this is the line on which a point will fall in the opposite eye. This line is tilted out of the horizontal unless the eyes are fixated on a very distant object.{/ss} {/s}equilluminant stimuli {s} {ss}Visual stimuli that vary only in colour but not in luminance. Stereopsis and motion perception disappear at equiluminance indicating the presence of separate processing channels for colour, motion and stereopsis.{/ss} {/s}erosion {s} {ct}image proc.{/ct} {ss}The converse of the morphology dilation operator. A morphological operation which moves a probe or structuring element of a particular shape over the image, pixel by pixel. When the probe fits inside an object boundary, a pixel is preserved in the output image. The effect is to "shrink or erode" objects as they appear in the output image. Any shape smaller than the probe (ie noise) disappears.{/ss} {/s}etendue {s} {ct}optics{/ct} {ss}Geometric etendue (geometric extent) characterises the ability of an optical system to accept light. Etendue is a constant of the system and is determined by the {em}least{/em} optimised segment of the entire optical system.{/ss} {/s}extrinsic camera parameters {s} {ct}comp. vis.{/ct} {ss}The parameters that relate the camera to the scene, such as the position of the camera in the global co-ordinate system.{/ss} {/s}false match {s} {ct}video proc.{/ct} {ss}Problem in {sa}motion estimation{/sa} where a motion vector is found that does not correspond to the true motion. Often caused by a lack of texture in the window/block that is being compared.{/ss} {/s}feature extraction {s} {ct}comp. vis.{/ct} {ss}Determining image features by applying feature detectors to distinguish or segment them from the background.{/ss} {/s}feature matching {s} {ct}comp. vis.{/ct} {ss}In binocular vision and stereopsis, disparity can be extracted from an image if features in the two corresponding binocular images are matchable; e.g. lines to lines, dots to dots.{/ss} {/s}feature vectors {s} {ct}comp. vis.{/ct} {ss}A set of features of an object (such as area, number of holes, etc) that can be used for its identification or inspection.{/ss} {/s}features {s} {ct}comp. vis.{/ct} {ss}Simple image data attributes such as pixel amplitudes, edge point locations and textural descriptors, centre of mass, number of holes in an object with distinctive characteristics defined by boundaries or regions.{/ss} {/s}Fechner's paradox {s} {ss}The fact that a monocular view may look brighter than a binocular view. Suppose that a scene is viewed through both eyes but that one eye sees it through a neutral filter that attenuates all wavelengths by a constant ratio. The filter does not distort the reflectances or ratios of light reaching the eye, but only its absolute intensity. If the filtered eye is entirely occluded the scene looks brighter and more vivid than with the filter despite the fact that less total light is reaching the two eyes and the reflectances are still the same.{/ss} {/s}fiducial {s} {ss}A line, mark or shape used as a standard of reference for measurement or location.{/ss} {/s}field {s} {ct}TV{/ct} {ss} One of the two parts of a television frame in an interlaced scanning system. The odd plus the even field comprise one video frame.{/ss} {/s}field of view {s} {ct}optics{/ct} {ss}The 2D area which can be seen through the optical imaging system (FOV).{/ss} {/s}filling-in theory {s} {ss}Idea that the brightness and colour of interiors of homogeneous regions are determined by a process of lateral spread of neural activation that is initiated by units responding to abrupt changes in luminance and wavelength.{/ss} {/s}first-order motion mechanisms {s} {ss}Captures motion information from moving objects or features that differ from the background in luminance. See {sa}second-order motion mechanisms{/sa}.{/ss} {/s}fixation {s} {ss}Alignment of the eyes so that the image of the fixated target falls on the area centralis. For animals with immobile eyes the alignment of the head towards the fixated target.{/ss} {/s}flicker {s} {ss}Alternating levels of brightness.{/ss} {/s}flicker photometry experiment {s} {ss}Stimuli consisting of a pair of different colour test lights alternate. When the lights alternate slowly the pattern appears to change between the colours of the two lights. When the lights alternate rapidly observers fail to see the colour modulation and instead perceive a dark-light modulation. Demonstrates that the temporal resolution for distinguishing blue-yellow is less than red-green which in turn is less than light-dark.{/ss} {/s}floater {s} {ct}biol.{/ct} {ss}A blurry spot that appears to float around in the eye but does not block vision. The blur is the result of debris from the vitreous humour casting a shadow on the retina.{/ss} {/s}fluorescence {s} {ss}The emission of light or other electromagnetic radiation at longer wavelengths by matter as a result of absorption of a shorter wavelength. The emission lasts only as long as the stimulating irradiation is present.{/ss} {/s}F-number or f-stop {s} {ct}optics{/ct} {ss}The ratio of the focal length to the lens aperture. The smaller the f number, the larger the lens diameter and brighter the image and narrower the depth of field.{/ss} {/s}focal length {s} {ct}optics{/ct} {ss}The distance from a lens' principal point to the corresponding focal point on the object.{/ss} {ss}Relates the distance between an image source and a lens ds and the distance of the lens to the image di by the lenses focal length f.{/ss} {/s}focal plane {s} {ct}optics{/ct} {ss}Usually found at the image sensor, it is a plane perpendicular to the lens axis at the point of focus.{/ss} {/s}focal vision {s} {ss}The role of vision involved in the examination and identification of objects associated with the fovea and exploratory eye movements. As opposed to {sa}ambient vision{/sa}.{/ss} {/s}focus {s} {ct}optics{/ct} {ss}The point at which rays of light converge for any given point on the object in the image. Also called the focal point.{/ss} {/s}focus following {s} {ss}A ranging and tracking technique that uses image processing to measure object range based on best focus.{/ss} {/s}focus pulling {s} {ct}TV{/ct} {ss}Changing the focus to a nearer object for dramatic effect.{/ss} {/s}foreshortening {s} {ct}3D, geom.{/ct} {ss}Perspective foreshortening is an effect that occurs when a surface is viewed at a sharp angle, can reduce the precision of stereo methods.{/ss} {/s}fovea {s} {ct}biol.{/ct} {ss}The area of the retina associated with the highest concentration of cones and therefore the highest acuity. Humans move their eyes so that images of interest are projected onto their foveas.{/ss} {/s}foveola {s} {ct}biol.{/ct} {ss}The centre of the fovea.{/ss} {/s}frame {s} {ct}video proc.{/ct} {ss}The total area scanned in an image sensor while the video signal is not blanked. In interlaced scanning, two fields comprise one frame.{/ss} {/s}frame cancellation effect {s} {ct}3D, HVS{/ct} {ss}When an object appears in front of a 3D display, the bezel of the display may appear to occlude the object destroying the illusion of depth.{/ss} {/s}Freedericksz transition {s} {ct}hw.{/ct} {ss}State where deformation of liquid crystal molecules occurs due to an external electric or magnetic field.{/ss} {/s}frustum {s} {ct}comp. graph.{/ct} {ss}The portion of a solid which lies between two parallel planes cutting the solid. Degenerate cases are obtained for finite solids by cutting with a single plane only.{/ss} {/s}fundamental matrix {s} {ct}comp. vis.{/ct} {ss}Matrix that describes the intrinsic and extrinsic camera parameters.{/ss} {/s}gamma {s} {ss}The numeric value for the degree of contrast in a television picture. The exponent in the power law relating output to input signal magnitude. Non-linear camera tube.{/ss} {/s}Ganzfeld phenomenon {s} {ss}A uniformly illuminated surface of a uniform field (a ganzfeld) quickly disappears from visual perception and one experiences a grey fog.{/ss} {/s}Gaussian filter {s} {ct}image proc.{/ct} {ss}Algorithm smoothing spatial or temporal variation in an image by averaging neighbouring values of light intensity, the contribution of values to the average being weighted according to a Gaussian function.{/ss} {/s}Gelb-experiment {s} {ss}A spinning black disc is illuminated by a projector in a darkly illuminated room. The disk appears to be white until a small white piece of paper is placed in front of the projected light at which time the true colour of the disk is perceived (i.e. black).{/ss} {/s}generic view {s} {ss}A view of an object that is not special. In other words, the view won't change drastically with small perturbations in lighting or viewing direction. (As opposed to {sa}accidental view{/sa}).{/ss} {/s}glints {s} {ss}Shiny, specular reflections from smooth objects or surfaces.{/ss} {/s}GOP {s} {pr}gop{/pr} {ct}standards{/ct} {ss}Group Of Pictures. An MPEG video stream may package a number of images together.{/ss} {/s}gradient {s} {ss}The rate of change of pixel intensity (first derivative).{/ss} {/s}gradient space {s} {ss}A matrix containing values for the rate of change of pixel values or grey level intensity of the image.{/ss} {/s}gradient vector {s} {ss}The orientation and magnitude of the rate of change in intensity at a point or pixel location in the image.{/ss} {/s}grey level {s} {ss}A quantised measurement of image irradiance (brightness), or other pixel property typically in the range between pure white and black.{/ss} {/s}greyscale image {s} {ss}An image consisting of an array of pixels which can have more than two values. Typically, up to 256 levels (8 bits) are used for each pixel.{/ss} {/s}haploscopic stimulation {s} {ss}Different stimuli for the two eyes.{/ss} {/s}Harris corner {s} {ct}image proc.{/ct} {ss}A type of image feature point.{/ss} {ss}A locally averaged moment matrix is computed from the image gradients then the eigenvalues are combined to compute a corner "strength", maximum values indicate corner positions.{/ss} {/s}HCF {s} {ct}opt.{/ct} {ss}Highest Confidence First. An optimisation algorithm: all sites are labelled as uncommitted. Once assigned a site cannot be unassigned. A stability measure is calculated for each site, unreliable sites do not affect through neighbour interaction. Terminate when reassignment brings no improvement.{/ss} {/s}HDMI {s} {ct}TV{/ct} {ss}High-Definition Multimedia Interface. An all digital audio-video interface for transmitting uncompressed audio and video streams.{/ss} {/s}HDTV {s} {ct}HDTV{/ct} {ss}High Definition TV, approximately 1920x1080 pixels comprise one frame. Although some claim that 720 lines progressive is "high" definition too.{/ss} {/s}Hermann grid illusion {s} {ct}HVS{/ct} {ss}Dark blobs appear at the intersections of black rectangles except when viewed foveally.{/ss} {/s}heterophoria {s} {ct}biol.{/ct} {ss}When the two eyes are misaligned when focusing on a point.{/ss} {/s}histogram analysis {s} {ss}Determination of the presence or absence of a feature or flaw based on the histogram values in a certain grey scale region.{/ss} {/s}histogram equalisation {s} {ss}Modification of the pixel values to evenly distribute a narrow range of image grey scale values across the entire available range.{/ss} {/s}HOE {s} {ct}optics, hw.{/ct} {ss}Holographic Optical Element.{/ss} {/s}hollow face illusion {s} {ct}HVS{/ct} {ss}A concave hollow mask of a face viewed from a few feet gives the impression of a normal face. The cognitive interpretation overrides the stereoscopic information.{/ss} {/s}homography {s} {ct}comp. vis., geom.{/ct} {ss}A 3x3 matrix that describes a 2D to 2D projective transformation.{/ss} {/s}horizontal cells {s} {ss}Cells in the retina connected via gap junctions that mediate lateral information transfer over large distances.{/ss} {/s}horopter {s} {ct}optics{/ct} {ss}Given a binocular system, to be seen as a model of the human eyes. The horopter then, is a 3D curve that can be defined as the set of points for which the light falls on corresponding areas in the two retinas. This definition seems to be equivalent to the intersection of a cylinder and a hyperbolic paraboloid. The term horopter seems to be derived from the words 'horizon' and 'optical'.{/ss} {ss}For a given fixation point, the set of points on the retina that are perceived to have zero retinal disparity. The points sweep out an arc in space that intersects a fixated point in space.{/ss} {/s}Hough transform {s} {pr}huff transform{/pr} {ss}A voting procedure working globally. Often used for locating both curved and straight lines. All points on the curve map into a single location in the transform space.{/ss} {/s}HSI {s} {ss}An acronym for the Hue Saturation Intensity colour representation. A mathematical conversion from RGB. Often used for machine vision analysis.{/ss} {/s}hue {s} {ss}One of the three properties of HSI colour perception. A colour attribute used to express the amount of red, green, blue or yellow a certain colour possesses. White, grey and black do not exhibit any hue.{/ss} {ss}The perception of colour. (See also {sa}saturation{/sa}).{/ss} {/s}Hueckel operator {s} {ct}image proc.{/ct} {ss}An edge finding operator which fits an intensity surface to the neighbourhood of each pixel and selects surface gradients above a specified threshold.{/ss} {/s}I2P {s} {pr}eye to pee{/pr} {ct}video proc.{/ct} {ss}Interlaced to Progressive conversion. A video sequence in interlaced format is converted to progressive format.{/ss} {/s}IBR {s} {ct}comp. vis.{/ct} {ss}Image Based Rendering. Technique used to fill in image details using parts of images taken from other viewpoints thus avoiding the need for 3D reconstruction.{/ss} {/s}ICM {s} {ct}opt.{/ct} {ss}Iterated Conditional Modes. An optimisation algorithm used for Markov random fields.{/ss} {/s}iconic memory {s} {ss}Short-lived visual sensory memory which lasts about 500 msec. Disrupted by masking (i.e. by a bright light). Tied to anatomical coordinates. (See also {sa}short-term visual store{/sa}).{/ss} {/s}illuminance {s} {ss}Amount of light falling onto a surface. (See also {sa}luminance{/sa}).{/ss} {/s}illumination {s} {ss}Normally a wavelength or range of wavelengths of light or visible light used to enhance a scene so the detector, normally a camera, can produce an image.{/ss} {/s}illusory contours {s} {ss}Contours which can be perceived in the absence of any real lines or edges.{/ss} {/s}image enhancement {s} {ss}Image processing operations which improve the visibility of image detail and features. Usually performed for humans.{/ss} {/s}image formation {s} {ss}Generation of an image of an object or scene on the imaging sensor. It includes effects from the optics, filters, illumination and sensor itself.{/ss} {/s}image intensifier {s} {ss}Usually an electron tube equipped with a light sensitive electron emitter at one end and a phosphor screen at the other. Used to provide electron gain for imaging in low light conditions such as night vision.{/ss} {/s}index of refraction {s} {ss}A property of a medium that measures the degree that light bends when passing between it and a vacuum.{/ss} {/s}integral image {s} {ct}3D{/ct} {ss}3D image formed using camera and display with microlens arrangement, see De Montfort University work, invented by Lippmann.{/ss} {/s}intensity {s} {ss}The relative brightness of a portion of the image or illumination source.{/ss} {/s}interlaced scanning {s} {ss}A scanning process in which all odd lines then all even lines are alternately scanned. Adjacent lines belong to different fields.{/ss} {/s}interocular motion display {s} {ss}A motion display in which the motion stimulus in each eye of the observer is ambiguous, yet perception of coherent motion is possible if the subject combines motion information from both the eyes.{/ss} {/s}intrinsic camera parameters {s} {ct}comp. vis.{/ct} {ss}Camera parameters relating specifically to the camera, such as focal length, position of the principal point and lens distortion.{/ss} {/s}IRLS {s} {ct}math.{/ct} {ss}Iteratively Reweighted Least Squares.{/ss} {/s}isomorphic {s} {ct}alg.{/ct} {ss}The property where two graphs have a one-one correspondence between their vertices and edges.{/ss} {/s}isophote {s} {ct}image. proc.{/ct} {ss}A curve on a graph joining points of equal light intensity.{/ss} {/s}isotropic {s} {ct}math.{/ct} {ss}The property where components remain unchanged under an arbitrary change of basis.{/ss} {ss}Any process or filter which is not directionally selective or biased. (As opposed to anisotropic).{/ss} {/s}Johnson's criteria {s} {ss}The number of raster lines of a display required to interpret different levels of objects within a displayed scene. These levels are: 1. No detection 2. Detection 3. Shape orientation 4. Shape recognition 5. Detail recognition. Sometimes used in training.{/ss} {/s}JPEG {s} {pr}jay-peg{/pr} {ct}standards, image proc.{/ct} {ss}Joint Photographic Experts Group.{/ss} {ss}An image-compression standard based on a linear transform called the discrete cosine transform (DCT). The image is first block coded, each block transformed using the DCT, the transform coefficient quantised, and then subjected to a lossless compression algorithm. Loses some information about high spacial frequencies and suffers from some block artefacts.{/ss} {/s}Kalman filter {s} {ct}sig. proc.{/ct} {ss}An optimal filtering algorithm.{/ss} {/s}Kell or Kell factor {s} {ct}TV{/ct} {ss}Used to quantify the loss of vertical resolution in a line-scan imaging system due to artefacts of sampling.{/ss} {/s}Keplerian view (of stereopsis) {s} {ss}Suggest two monocular views are projected point-by-point along diagonal rays and that their crossing-points are loci from which the depth of objects may be computed.{/ss} {/s}kinetic depth effect {s} {ct}HVS{/ct} {ss}In a dynamic scene, the motion of 2D lines may give the appearance of structure, e.g. a rotating wire cube.{/ss} {ss}{/ss} {/s}KLT {s} {ss}Karhunen-Loeve Transform.{/ss} {/s} {s} {ss}Kanade-Lucas-Tomasi feature.{/ss} {/s}Koffka-Benussi ring illusion {s} {ss}The addition of an intervening line can change the perceived lightness of the two sides of a ring with uniform luminance.{/ss} {/s}Kronecker delta function {s} {ct}sig. proc.{/ct} {ss}A 2D delta function.{/ss} {/s}L cones {s} {ct}biol.{/ct} {ss}Long wavelength sensitive cones (red). Are most sensitive to a wavelength of approximately 558 nm. (See also {sa}M cones{/sa} and {sa}S cones{/sa}).{/ss} {/s}LAB {s} {ss}CIELAB colour gets its name from a colour space that uses three values to describe the precise three-dimensional location of a colour inside a visible colour space CIE stands for Commission Internationale de l-Eclairages an international body of colour scientists whose standards make it possible to communicate colour information accurately L describes relative lightness; A represents relative redness-greenness,and B represents relative yellowness-blueness.{/ss} {/s}Lambertian surface {s} {ct}optics{/ct} {ss}An ideal diffuse surface for which reflected light brightness is dependent on viewing angle.{/ss} {/s}Laplacian operator {s} {ss}The sum of the second derivatives of the image intensity in both the x and y directions is called the Laplacian. The Laplacian operator is used to find edge elements by locating points where the Laplacian in zero.{/ss} {/s}laser radar {s} {ss}See {sa}LIDAR{/sa}.{/ss} {/s}layering {s} {ct}HVS{/ct} {ss}Creating illusion of depth by using parallax layers.{/ss} {/s}LCOS {s} {ct}hw.{/ct} {ss}Liquid Crystal on Silicon.{/ss} {/s}LCS {s} {ct}hw.{/ct} {ss}Liquid Crystal Shutter (eye wear), usually used to deliver time multiplexed images to each eye so that stereo is achieved.{/ss} {/s}lenticular display {s} {ct}3D{/ct} {ss}See {sa}integral image{/sa}.{/ss} {/s}LIDAR {s} {ct}hw.{/ct} {ss}An acronym of Light Detection And Ranging. A system that uses light instead of microwaves for range and tracking measurements. LIDAR uses a laser light source to measure velocity, altitude, height, range or profile {/ss} {/s}lightness {s} {ss}The perception of reflectance. Related to the perception of an object's surface.{/ss} {/s}lightness constancy {s} {ss}Objects are perceived to maintain a relatively constant surface lightness despite changes in illumination (Type I) or background colour (Type II).{/ss} {/s}line scan camera {s} {ct}hw.{/ct} {ss}A solid state video camera consisting of a single row of pixels. Also called a linear array or pushbroom camera.{/ss} {/s}linear array {s} {ss}See {sa}line scan camera{/sa}.{/ss} {/s}linespread {s} {ss}The distribution of how the image of a very thin line is blurred on the retina (due to diffraction). Depends on pupil size.{/ss} {/s}LM {s} {ct}opt.{/ct} {ss}Levenberg-Marquardt. Approximation to second order gradient descent method.{/ss} {/s}lossless compression {s} {ss}An image compression method which preserves image information perfectly. For example, as nearby pixels in an image are usually similar (highly correlated), one can eliminate this redundancy by coding one pixels intensity I(x,y), and subsequent pixels by their difference rather than the values themselves. The new representation has a lower correlation and requires less storage space despite preserving all information. The best possible lossless compression is one in which the values are completely decorrelated as correlation (the ability to predict one value from another) is a sign of redundancy.{/ss} {/s}lossy compression {s} {ct}image proc.{/ct} {ss}Image processing techniques which save space but do lose some information about the contents of an image.{/ss} {/s}low angle illumination {s} {ss}Very useful to enhance and highlight surface texture features.{/ss} {/s}luminance {s} {ss}Amount of light coming off of a surface. Subjectively, the unit of brightness measured in candela per meter squared (cd/m2).{/ss} {/s}M cones {s} {ct}biol.{/ct} {ss}Medium wavelength sensitive cones (green). Are most sensitive to a wavelength of approximately 531 nm. (See also {sa}L cones{/sa} and {sa}S cones{/sa}).{/ss} {/s}M estimator {s} {ct}math.{/ct} {ss}Estimates the optimal parameters for an error metric based on the structure of the data. From robust statistics and influence functions.{/ss} {/s}Mach bands {s} {ct}HVS{/ct} {ss}Bright and dark lines that appear near the brighter and darker borders of a blurred edge between two uniform regions of different luminance. Luminance ramps which are too steep or too shallow do not create mach bands.{/ss} {/s}machine vision {s} {ss}The use of devices for optical non-contact sensing to automatically receive and interpret an image of a real scene, in order to obtain information and/or control machines or processes. {/ss} {/s}MAD {s} {ss}See {sa}mean absolute difference{/sa}.{/ss} {ss}Median Absolute Deviation. A measure of statistical scale, often used in robust statistics.{/ss} {/s}MAP {s} {ct}alg.{/ct} {ss}Maximum a Posteriori. Principle used when performing stochastic optimisation.{/ss} {/s}mass function {s} {ct}math.{/ct} {ss}The PDF of a discrete random variable.{/ss} {/s}matrix array camera {s} {ct}hw.{/ct} {ss}See area array camera.{/ss} {/s}MC {s} {ct}video proc.{/ct} {ss}See {sa}motion compensation{/sa}.{/ss} {/s}MDL {s} {ct}alg.{/ct} {ss}Minimum Description Length.{/ss} {/s}mean absolute difference {s} {ss}An error metric, commonly used in motion estimation.{/ss} {/s}mesopic {s} {ss}Intensities of light under which both rods and cones operate. (See also {sa}photopic{/sa} and {sa}scotopic{/sa}).{/ss} {/s}MHP {s} {ct}standards{/ct} {ss}Multimedia Home Platform. Defined by the DVB project, MHP describes a generic interface between an application and the terminal it is running on.{/ss} {/s}ML {s} {ct}alg.{/ct} {ss}Maximum Likelihood.{/ss} {/s}MLE {s} {ct}alg.{/ct} {ss}Maximum Likelihood Estimation.{/ss} {/s}monochromatic {s} {ss}Refers to light having only one colour or a single wavelength of radiation.{/ss} {/s}monochrome {s} {ss}Refers to a black and white image with shades of grey but no colour.{/ss} {/s}monocular depth cues {s} {ss}Relative size, texture gradients, perspective, shadow, height of retina image, interposition, motion parallax.{/ss} {/s}monotonicity constraint {s} {ct}geom., comp. vis.{/ct} {ss}The relative ordering of points along epipolar lines is preserved.{/ss} {/s}morphology {s} {ct}image proc.{/ct} {ss}Image algebra group of mathematical operations based on manipulation and recognition of shapes. Also called mathematical morphology. Operations may be performed on either binary or grey scale images.{/ss} {/s}mosaic {s} {ct}comp. vis.{/ct} {ss}Image formed from joining multiple images that have been registered to one another.{/ss} {/s}mosquito noise {s} {ct}image proc., video proc.{/ct} {ss}Sometimes seen around the edges of moving objects, and characterised by moving artefacts around edges and/or by blotchy noise patterns superimposed over the objects, resembling a mosquito flying around a person's head and shoulders. Often found in images compressed using the {sa}DCT{/sa} at low bit rates.{/ss} {/s}motherglass {s} {ct}hw.{/ct} {ss}Large, high quality area of glass used to cut into multiple pieces as substrates for liquid crystal displays.{/ss} {/s}motion compensation {s} {ct}video proc.{/ct} {ss}Using motion vectors obtained from {sa}motion estimation{/sa} to transform an image.{/ss} {/s}motion estimation {s} {ct}video proc.{/ct} {ss}Determining the apparent motion of objects in a video sequence by finding motion vectors that map the position of objects in one frame to their corresponding position in another frame.{/ss} {/s}motion parallax {s} {ss}Movement of the image of an object over the retina. The rate of movement depends upon the velocity of the object relative to the eye and its distance from the eye.{/ss} {/s}motor fusion {s} {ct}3D, biol.{/ct} {ss}Changing the vergence of the two eyes so that images that fall on different points in the two retinas come to fall upon corresponding places in the central retinas. (As opposed to {sa}sensory fusion{/sa}).{/ss} {/s}MP@ML {s} {ct}standards, video proc.{/ct} {ss}Main Profile at Main Level. From MPEG-2.{/ss} {/s}MPEG {s} {pr}em-peg{/pr} {ct}standards, video proc.{/ct} {ss}Motion Picture Experts Group. MPEG produce a number of standards for video coding and video metadata. While MPEG defines what form the information is stored in their standards do not specify what method is used to generate the representation, therefore there is no "MPEG algorithm".{/ss} {/s}MPEG-PS {s} {ct}standards{/ct} {ss}MPEG Program Stream. Audio and video packaged together.{/ss} {/s}MPEG-TS {s} {ct}standards{/ct} {ss}MPEG Transport Stream. A program stream in suitable packetised format for broadcasting.{/ss} {/s}MSE {s} {ss}Mean Squared Error. An error metric, often used in block matching algorithms.{/ss} {/s}Muller-Lyer illusion {s} {ss}Two lines of equal length appear to unequal.{/ss} {/s}myopia {s} {ss}An eye is myopic when the "far point"; a point at which light from an object is focused on the retina, is located at a finite distance in front of the eye. Myopia can be due to either an eye which is too long relative to the optical power of the eye (axial myopia), or because the optical power of the eye is too high relative to the length of the standard eye (refractive myopia). The focus is correctly adjusted with a "minus" power lens, or concave lens. Myopia is often referred to as "short-sightedness" or "near-sighted".{/ss} {/s}nematic {s} {ct}hw.{/ct} {ss}The phase of a liquid crystal characterised by arrangement of the long axes of the molecules in parallel lines but not layers.{/ss} {/s}neon-colour spreading {s} {ss}A phenomenon in which the colour certain stimuli seem to "leak" into surrounding areas. For example using a red cross and an Ehrenstein figure. When the solid red-cross is perceived in isolation it looks normal. When the Ehrenstein figure is viewed in isolation it generates an illusory contour. When the red cross is places in the Ehrenstein figure, the red colour flows out of the cross and tends to fill the illusory figure.{/ss} {/s}NTSC {s} {ct}TV, standards{/ct} {ss}National Television Standards Council. NTSC is a standard for encoding the colour in analogue TV transmissions. See also {sa}PAL{/sa} and {sa}SECAM{/sa}.{/ss} {/s}NVS {s} {ct}comp. vis.{/ct} {ss}Novel View Synthesis. Technique to create new views using images from calibrated cameras, disparity maps etc.{/ss} {/s} OBASC {s} {ct}alg.{/ct} {ss}Object Based Analysis Synthesis Coding. Used for video coding.{/ss} {/s}object centred coordinate system {s} {ss}A structural description of an object independent of viewpoint.{/ss} {/s}occlusion {s} {ct}video proc.{/ct} {ss}When part of an image is hidden behind another part, such as a moving object in the foreground, or self occlusion when protrusion on an object covers part of itself.{/ss} {ss}Occlusion is a strong monocular depth cue.{/ss} {/s}opening {s} {ct}image proc.{/ct} {ss}An erosion followed by a dilation, it is the opposite of the closing morphological operator.{/ss} {/s}opsin {s} {ct}biol.{/ct} {ss}Protein portion of rhodopsin.{/ss} {/s}opthalmoscope {s} {ct}optics{/ct} {ss}Device for seeing light reflected from the interior of the eye.{/ss} {/s}optic chiasm {s} {ct}biol.{/ct} {ss}Location where the optic nerve axons from the two retinae join and are reorganised into two separate groups (the optic tracts) that encode information about the right and left visual fields.{/ss} {/s}optical power (of a lens) {s} {ct}hw.{/ct} {ss}Measure of how strongly a lens bends incoming rays. Measured in dioptres and equal to the reciprocal of focal length. Human eye has an optical power of about 58.8 dioptres.{/ss} {/s}orthoscopic {s} {ct}3D, geom.{/ct} {ss}Giving an image in correct and normal proportions. Used to denote a correctly arranged stereo pair of images. Opposite of {sa}pseudoscopic{/sa}.{/ss} {/s}Ouchi illusion {s} {ct}HVS{/ct} {ss}A {sa}peripheral drift{/sa} illusion using a small orthogonal checkerboard pattern on a background with the checkerboard in an orthogonal aspect.{/ss} {/s}PAL {s} {ct}TV, standards{/ct} {ss}Phase Alternate Line. Method for encoding the colour on a TV broadcast. The phase of the colour vector is inverted on alternating lines in order to reduce the error. See also {sa}NTSC{/sa} and {sa}SECAM{/sa}.{/ss} {/s}palinopsia {s} {ct}biol., HVS{/ct} {ss}(Literally 'seeing again') is a form of visual perseveration. It refers to reappearance of an image after some time when the original external stimulus is no longer available. Neural basis of palinopsia is unknown but many palinopsia patients have some right-hemisphere disturbances.{/ss} {/s}Panum's fusional area {s} {ct}HVS, 3D{/ct} {ss}The area in which fusion can occur.{/ss} {ss}Region of space within which perception of a single object is possible. (See also {sa}stereopsis{/sa}).{/ss} {/s}Panum's limiting case {s} {ct}HVS, 3D{/ct} {ss}The minimum conditions for the perception of stereopsis consisting of three lines, one for one eye and two for the other.{/ss} {/s}parallactiscope {s} {ct}3D{/ct} {ss}A version of a stereoptiplexer but using a CRO with 360 degrees freedom.{/ss} {/s}parallax {s} {ct}3D{/ct} {ss}The change in perspective of an object when viewed from two slightly different positions. The object appears to shift position relative to its background, and also appears to rotate slightly.{/ss} {/s}parallax barrier {s} {ct}3D{/ct} {ss}A series of lines covering a display with the correct geometry can block light from some pixels and thus achieve a series of zones in front of the display where only part of the display can be seen. This allows a 3D display to be created.{/ss{ {/s}parallax panoramagram {s} {ct}3D{/ct} {ss}An extension to the {sa}parallax barrier{/sa} method, reducing the width/pitch ratio giving a wider viewing angle for each viewing zone.{/ss} {/s}pathological motion {s} {ct}video proc.{/ct} {ss}A motion estimation scenario where the type of motion or the two images being used to estimate the motion do not contain enough information in order to estimate a reasonably accurate motion vector.{/ss} {/s}pattern recognition {s} {ct}comp. vis,{/ct} {ss}A process which identifies an object based on analysis of its features.{/ss} {/s}PBS {s} {ct}optics, hw.{/ct} {ss}Polarisation Beam Splitter.{/ss} {/s}PCA {s} {ct}alg.{/ct} {ss}Principal Component Analysis.{/ss} {/s}PCOS {s} {ct}optics, hw.{/ct} {ss}Polarisation Conversion Optical System.{/ss} {/s}PDP {s} {ct}hw., TV{/ct} {ss}Plasma Display Panel. A type of display.{/ss} {/s}perceptual constancy {s} {ss}The phenomenon that the perception of an object remains constant despite changes in its size, lighting conditions and orientation.{/ss} {/s}perceptually lossless compression {s} {ct}image proc.{/ct} {ss}An image processing technique which loses some information about contents of the image, but the distortions produced by the loss aren't visible to the human image processing system.{/ss} {/s}peripheral drift {s} {ct}HVS{/ct} {ss}An anomalous motion illusion that can be observed in peripheral vision.{/ss} {/s}photodiode {s} {ct}hw.{/ct} {ss}A single photoelectric sensor element, either used stand-alone or a pixel site, part of a larger sensor array.{/ss} {/s}photometry {s} {ss}Measurement of light which is visible to the human eye (photopic response).{/ss} {/s}photon noise {s} {ss}The fact that a stream of photons is not steady but fluctuates in intensity around an average value.{/ss} {/s}photopic {s} {ct}biol.{/ct} {ss}Bright light conditions where only the cones are functional. (See also {sa}mesopic{/sa} and {sa}scotopic{/sa}).{/ss} {/s}photopic response {s} {ct}biol.{/ct} {ss}The colour response of the eye's retinal cones.{/ss} {/s}phototransduction {s} {ss}The transformation of incoming light to a neural impulse.{/ss} {/s}picket fence effect {s} {ct}3D{/ct} {ss}An effect that can occur when a {sa}parallax barrier{/sa} is very visible.{/ss} {/s}POCS {s} {ct}alg.{/ct} {ss}Projection Onto Convex Sets.{/ss} {/s}Poggendorf illusion {s} {ct}HVS{/ct} {ss}Perception of collinearity can be distorted by an intervening figure.{/ss} {/s}point spread {s} {ss}A measure of optical blur produced by natural imperfections of the lens of the eye. The response to a point of light produces a certain amount of blur, the amount of this blurring is known as the point spread.{/ss} {/s}polarised light {s} {ct}optics{/ct} {ss}Light which has had the vibrations of the electric or magnetic field vector typically restricted to a single direction in a plane perpendicular to its direction of travel. It is created by a type of filter which absorbs one of the two perpendicular light rays. Crossing polarisers theoretically blocks all light transmission.{/ss} {/s}polariser {s} {ct}optics{/ct} {ss}An optical device which converts natural or unpolarised light into polarised light by selective absorption of rays in one direction, and passing of rays perpendicular to the polarising medium. Usually fabricated from stretched plastic sheets with oriented, parallel birefringent crystals. The first polarisers were constructed with parallel wires.{/ss} {/s}Ponzo illusion {s} {ct}HVS{/ct} {ss}When two horizontal rods of equal length are drawn over an upside down V the upper rod appears longer than the lower rod.{/ss} {/s}pool hypothesis {s} {ss}Hypothesis for the mechanism for stereopsis. Suggests the visual system contains three pools, one for crossed disparities, one for uncrossed disparities and one for non-zero disparities. A particular depth is signalled by the relative activity of crossed and uncrossed pools rather than by a sharply tuned neuron coding a particular depth.{/ss} {/s}pop-out {s} {ss}Target items in a visual search that have features which allow them to be detected quickly regardless of the number of distractors presents are said to "pop-out".{/ss} {/s}Prewitt filter {s} {ct}image proc.{/ct} {ss}Edge detecting 3x3 kernel filter. Very similar to {sa}Sobel filter{/sa} but with no emphasis on the central edge.{/ss} {/s}procam {s} {ct}comp. vis.{/ct} {ss}Projector-Camera system. A projector is used as a programmable flash in order to capture information about the scene with a camera(s). See also {sa}campro{/sa}.{/ss} {/s}protocols {s} {ct}3D, HVS, comp. graph.{/ct} {ss}{sa}Sharp{/sa} in-house term for controlling the amount of depth in a 3D image so that the amount of depth in the scene comfortably fits within acceptable limitations from psychological studies, also preventing apparent scaling of objects as a stereo camera moves. See also {sa}squinching{/sa}.{/ss} {/s}pseudoscopic {s} {ct}3D, geom.{/ct} {ss}Where the left and right images of a stereo pair are swapped so each eye is seeing the wrong image. Opposite of {sa}orthoscopic{/sa}.{/ss} {/s}PSNR {s} {ct}image proc.{/ct} {ss}Peak Signal to Noise Ratio. Used to measure image similarity (in dB), although like all such metrics can easily be fooled by images that are not similar.{/ss} {/s}Pulfrich effect {s} {ct}3D, HVS{/ct} {ss}The brain processes dim images more slowly than bright images so a 3D effect is achieved if an object or image is continually rotating and one eye is covered with a dark filter.{/ss} {/s}pulldown {s} {ct}video proc., TV{/ct} {ss}Process used by a {sa}telecine{/sa} to convert from film frame rate to TV frame rate. Consecutive images from film are repeated in 3:2 ratio (NTSC) or 2:2 (PAL) in order to upconvert the frame rate.{/ss} {/s} puppet theatre effect {s} {ct}3D{/ct} {ss}When 3D objects look unnaturally small, due to the mismatch between perceived depth of an image on a display and the real world image.{/ss} {/s}QBIC {s} {ct}comp. vis.{/ct} {ss}Query By Image Content. Search term used for video databases. Uses image properties such as colour percentages, colour layout, and textures.{/ss} {/s}radial basis function {s} {ct}geom.{/ct} {ss}The response decreases monotonically from a fixed point.{/ss} {/s}radiometry {s} {ct}optics{/ct} {ss}Measurement of light within the entire optical spectrum.{/ss} {/s}random dot stereogram {s} {ct}HVS{/ct} {ss}A pair of images consisting of a uniform randomly generated texture of dots. No form is recognisable in the pair, but when fused, displacement of textural elements produces the perception of depth. Evidence against the use of monocular contours for stereopsis.{/ss} {/s}raster scan {s} {ct}hw., TV{/ct} {ss}A scanning pattern, generally from left to right while progressing from top to bottom of the imaging sensor or the display monitor. Generally comprised of two fields composed of odd and even lines.{/ss} {/s}RBF {s} {ct}geom.{/ct} {ss}See {sa}radial basis function{/sa}.{/ss} {/s}rectification {s} {ct}comp. vis.{/ct} {ss}Process of using the {sa}camera calibration{/sa} to reproject images so that they lie on the same plane.{/ss} {/s}rectilinear {s} {ct}comp. vis.{/ct} {ss}Parallel, side by side camera set up (not requiring {sa}rectification{/sa}).{/ss} {/s}redescending {s} {ct}opt.{/ct} {ss}An optimisation function property where all observations lying farther away than some upper bound are discarded.{/ss} {/s}reflectance {s} {ct}optics{/ct} {ss}The fraction of incident light that is reflected toward the eye by an object. (See {/ss} {/s}reflective LCD {s} {ct}hw.{/ct} {ss}Reflective displays rely on light entering the front of the display, either from a natural or integrated front light. Other types include {sa}transmissive LCD{/sa} and {sa}transflective LCD{/sa}.{/ss} {/s}refraction {s} {ss}The bending of light rays as they pass from one medium (e.g. air) to another (e.g. glass), each with a different index of refraction.{/ss} {/s}refringence {s} {ct}optics{/ct} {ss}Refractive power.{/ss} {/s}registration {s} {ct}image proc.{/ct} {ss}The closeness of the part to the actual position expected for image acquisition.{/ss} {/s}regression {s} {ct}opt.{/ct} {ss}An appraisal technique that states that between dissimilar properties, the value of the better quality property is adversely affected by the presence of the lesser quality property.{/ss} {/s}retardance {s} {ct}optics{/ct} {ss}The phase advancement given the distance travelled and the phase shift.{/ss} {/s}reticle {s} {ct}hw.{/ct} {ss}An optical element with a pattern located in the image plane to assist in calibration, measurement or alignment of a system or instrument. Examples are cross lines or grids.{/ss} {/s}RGB {s} {ct}image proc.{/ct} {ss}An acronym for the Red Green Blue colour space. This three primary colour system is used for video colour representation.{/ss} {/s}rhodopsin {s} {ct}biol.{/ct} {ss}The visual pigment in rod cells. Contains opsin and retinal.{/ss} {/s}Ricci flow {s} {ss}A parabolic system of partial differential equations which acts like the heat equation to spread the curvature of a Riemannian metric evenly over the surface to produce a metric of constant curvature. Computational Ricci flow has been invented and applied for computing hyperbolic structures and {sa}conformal surface{/sa} parameterisations.{/ss} {/s}Riemann surface {s} {ct}comp. graph.{/ct} {ss}A surface with a {sa}conformal structure{/sa} is called a {sa}Riemann surface{/sa}. All metric surfaces are Riemann surfaces.{/ss} {/s}ringlight {s} {ct}hw.{/ct} {ss}A circular lamp or bundles of optical fibres arranged around the perimeter of an objective lens to illuminate the object in the field below it. A wide variety of sizes are available on both a stock and custom basis.{/ss} {/s}rivalry {s} {ss}See {sa}binocular rivalry{/sa}.{/ss} {/s}rod {s} {ss}Photoreceptor for dim light conditions. Achromatic, lower acuity and temporal resolution than cones, outnumber cones 20 to 1. Rod system is convergent (many rods target one bipolar cell). (See also {sa}cone{/sa}).{/ss} {/s}RPTV {s} {ct}TV, hw.{/ct} {ss}Rear Projection Television.{/ss} {/s}S cones {s} {ct}biol.{/ct} {ss}Short wavelength sensitive cones (blue). Are most sensitive to a wavelength of approximately 419 nm. (See also {sa}L cones{/sa} and {sa}M cones{/sa}).{/ss} {/s}SAD {s} {ss}Sum of absolute differences. An error metric commonly used in motion estimation.{/ss} {/s}saturation {s} {ct}image proc.{/ct} {ss}The degree to which a colour is free of white. One of the three properties of colour perception along with hue and intensity (HSI).{/ss} {ss}The richness of hue. Indicates how much a colour has been diluted by greyness. (See also {sa}hue{/sa}).{/ss} {/s}scale invariant feature transform {s} {ct}comp. vis.{/ct} {ss}The original image is blurred to generate scale space by cascaded filtering. Features are extracted from the difference of these images. The features are invariant to scale and rotations.{/ss} {/s}scattering {s} {ct}optics{/ct} {ss}Redirection of light reflecting off a surface or through an object. See {sa}diffuse{/sa}. {/ss} {/s}scotopic {s} {ct}biol.{/ct} {ss}Dim light conditions where only rods are functional. (See also {sa}photopic{/sa} and {sa}mesopic{/sa}).{/ss} {/s}SEA {s} {ct}video proc.{/ct} {ss}Successive Eliminations Algorithm. A {sa}motion estimation{/sa} algorithm.{/ss} {/s}SECAM {s} {ct}TV, standards{/ct} {ss}Sequential Couleur Avec Memoire. Method for encoding colour in analogue television.{/ss} {/s}second-order motion mechanisms {s} {ss}Capture motion information from moving properties such as a moving are of flicker in which there is no difference in mean luminance between target and background. (See also {sa}first-order motion mechanisms{/sa}).{/ss} {/s}segmentation {s} {ct}image proc.{/ct} {ss}The process of dividing a scene into a number of individual objects or contiguous regions, differentiating them from each other and the image background.{/ss} {/s}sensory fusion {s} {ss}The combining of drawing together of two images which fall on different points in the two retinas without changing the vergence of the two eyes. (As opposed to {sa}motor fusion{/sa}).{/ss} {/s}shading {s} {ss}The variation of the brightness or relative illumination over the surface of an object, often caused by colour variations or surface curvature.{/ss} {/s}shape from shading {s} {ct}comp. vis., 3D{/ct} {ss}A 3D reconstruction technique.{/ss} {ss}A technique that uses shadows from interaction of the object and the light source to determine shape.{/ss} {/s}Sharp {s} {ct}hw.{/ct} {ss}Japanese company manufacturing 2D, 3D and multiview LCDs.{/ss} {/s}sharpening {s} {ct}image proc.{/ct} {ss}An image processing operation which enhances edges. An unsharp mask adds a low pass filtered image to the original, resulting in edge enhancement.{/ss} {/s}SIFT {s} {ct}comp. vis.{/ct} {ss}See {sa}scale invariant feature transform{/sa}.{/ss} {/s}silhouette {s} {ss}A black and white image of an object illuminated by backlighting.{/ss} {/s}simulated annealing {s} {ct}opt.{/ct} {ss}An optimisation process where at each stage the iteration is subject to random perturbation. A temperature parameter controls the probability that an increase in the criterion function allowed. The temperature starts off high but is cooled.{/ss} {/s}simultaneous contrast {s} {ss}An object of moderate reflectance appears relatively brighter or darker according to whether spatially adjacent regions are considerably darker or brighter than the object itself.{/ss} {/s}singular value decomposition {s} {ct}alg.{/ct} {ss}A method for image compression. Defines a linear transformation from a set of image data to a new representation with statistically independent values that range over smaller values. Also know as the Karhunen-Love Transform ({sa}KLT{/sa}) and the Hoteling transform.{/ss} {/s}singular views {s} {ct}3D, comp. vis.{/ct} {ss}A stereo camera configuration that cannot be made parallel, the optical centre of one camera is in the field of view of the other camera and warping cannot change the field of view.{/ss} {/s}size constancy {s} {ss}The fact that the perception of the sizes of objects remains remarkably constant at varying distance despite the fact that the image projected on the retina changes.{/ss} {/s}SLM {s} {ss}See {sa}spatial light modulator{/sa}.{/ss} {/s}snake {s} {ct}geom.{/ct} {ss}A deformable closed contour used in image analysis applications. Uses a elastodynamic model with applied forces for edge and curve detection. The energy of a stretchy, flexible contour (a snake) with tension and rigidity is minimised, while the snake itself is attracted to areas of darkness, brightness and/or intensity edges. Can be used to track objects over time as the potential function for the image changes from frame to frame.{/ss} {/s}Sobel filter {s} {ct}image proc.{/ct} {ss}A 3x3 kernel filter used for edge enhancement and location.{/ss} {/s}SOCP {s} {ct}opt.{/ct} {ss}Second Order Cone Programming.{/ss} {/s}spatial light modulator {s} {ct}optics, hw.{/ct} {ss}(Also SLM) A transparent screen used in optical computer systems to introduce an image into the optical processing path.{/ss} {/s}spectral efficiency {s} {ss}The relative luminous efficiency of light as a function of wavelength.{/ss} {/s}spectral response {s} {ss}The characteristic of a sensor to respond to a distribution of light by wavelength in the electromagnetic spectrum.{/ss} {/s}specular reflection {s} {ss}Light rays that are highly redirected at or near the same angle of incidence to a surface. Observation at this angle allows the viewer to "see" the light source.{/ss} {/s}SPIHT {s} {ct}alg.{/ct} {ss}Set Partitioning In Hierarchical Trees. A coding algorithm that exploits the correlation between subbands in a wavelet decomposed image.{/ss} {/s}Springer illusion {s} {ss}A dot pattern produces the perception of faint diagonal lines.{/ss} {/s}squinching {s} {ct}3D, HVS, comp. graph.{/ct} {ss}Normalising the depth of a 3D image to fit the human visual system. See {sa}protocols{/sa}.{/ss} {/s}SSE {s} {ss}Sum of Squared Errors. An error metric used in block matching algorithms.{/ss} {/s}stadimetry {s} {ss}A range measuring technique based on the apparent size measurement of a known size object in the field of view.{/ss} {/s}stereo (passive) {s} {ss}For imaging, the use of two cameras, offset by a known distance and angle, to image the same object and provide range, depth or 3D information. Active stereo uses a controlled or structured light source to provide 3D data.{/ss} {/s}stereobase {s} {ct}3D{/ct} {ss}The interaxial separation: the distance between the eyes (or cameras).{/ss} {/s}stereojet {s} {ct}3D, hw.{/ct} {ss}A method of printing a stereo image: Two images are printed and sandwich a polarising layer. The top image must be transparent. Polarising glasses are used to view.{/ss} {/s}stereopsis {s} {ct}3D, HVS{/ct} {ss}Process of forming a stereo image.{/ss} {ss}Perception of depth dependent upon disparity in the images projected on the retinas of the two eyes{/ss} {/s}stereoptiplexer {s} {ct}3D{/ct} {ss}A type of {sa}parallax barrier{/sa} that uses a rotating slit in a cylindrical drum, similar in several respects to the zoetrope.{/ss} {/s}stereoscope {s} {ct}3D{/ct} {ss}Device for creating a 3D image of a drawn objects. Works by projecting two different images of the objects to the eyes.{/ss} {/s}Stiles-Crawford effect {s} {ct}biol.{/ct} {ss}Light entering the eye through the centre of the pupil is more effective than light entering at a peripheral point near the edge of the pupil. This is largely to to the directionally sensitive photoreceptors which are oriented toward the centre of the pupil. This helps to minimise the effect of stray light.{/ss} {/s}stroop effect {s} {ct}HVS{/ct} {ss}When subjects are asked to name the colours of the ink in which the words are printed, their performance is considerably slowed if the words themselves are the names of other colours.{/ss} {/s}structured light {s} {ss}Points, lines, circles, sheets and other projected configurations used to directly determine shape and/or range information by observing their deformation as it intersects the object in a known geometric configuration.{/ss} {/s}successive contrast effect {s} {ss}The surface of a given luminance can appear darker or lighter depending on if the preceeding luminance was lower or higher.{/ss} {/s}SVD {s} {ss}See {sa}singular value decomposition{/sa}.{/ss} {/s}Swan's cube {s} {ct}3D, hw.{/ct} {ss}A cube made from two triangular prisms; light from one of the images is seen directly through both prisms by one eye, whereas light from the other image undergoes total internal reflection at the interface and is directed to the other eye.{/ss} {/s}sweet spot indicator {s} {ct}hw.{/ct} {ss}A piece of optics based hardware designed for 3D/multiview displays to show the user when he/she is in the correct viewing zone.{/ss} {/s}telecine {s} {ct}TV{/ct} {ss}Machine that scans film producing interlaced images suitable for TV.{/ss} {/s}template {s} {ct}video proc., comp. vis.{/ct} {ss}An artificial model of an object or a region or feature within an object.{/ss} {/s}template matching {s} {ss}A form of correlation used to find out how well two images match.{/ss} {ss}An object recognition method. Incoming patterns are matched against a set of templates. If there is sufficient overlap between object and template, a match is signalled. {/ss} {/s}tetrachromatic colour vision {s} {ss}Colour vision based on four cone photoreceptor pigments in the retina. The fourth cone type is sensitive to U.V. light and seen in goldfish.{/ss} {/s}texture {s} {ss}The degree of smoothness of an object surface. Texture affects light reflection, and is made more visible by shadows formed by its vertical structures.{/ss} {ss}The video processing term for pixels that possess the quality of varying value, as opposed to pixels that are highly similar to their neighbours.{/ss} {/s}top hat {s} {ct}image proc.{/ct} {ss}A morphological operator comprised of an opening followed by a subtraction of the output image from the original input image.{/ss} {/s}transflective LCD {s} {ct}hw.{/ct} {ss}Have a reflective rear polariser that also transmits light from the rear of the display.{/ss} {/s}transmissive LCD {s} {ct}hw.{/ct} {ss}Transmissive displays depend on light entering the back of the display in order to be seen.{/ss} {/s}transmittance {s} {ct}optics{/ct} {ss}The ratio of the radiant power transmitted by an optical element or object to the incident radiant power.{/ss} {/s}trichromatic colour vision {s} {ct}biol.{/ct} {ss}Colour vision based on three cone photoreceptors pigments in the retina.{/ss} {/s}trucking {s} {ct}HVS{/ct} {ss}See {sa}layering{/sa}.{/ss} {/s}TSS {s} {ct}video proc.{/ct} {ss}Three Step Search. A block matching algorithm.{/ss} {/s}twitter {s} {ct}TV{/ct} {ss}Also known as line twitter or inter-line flicker. When the edge of an object appears to be on lines in both fields of an interlaced image. The object appears to be moving up and down at frame frequency.{/ss} {/s}varifocal display {s} {ct}3D, hw.{/ct} {ss}Type of {sa}volumetric display{/sa}; some systems use a membrane mirror that can be deformed to be concave and convex; if an image is viewed in the mirror it will appear to advance and retreat as the mirror is deformed. Images are changed to correspond to different depths but must also cope with magnification changes in the mirror.{/ss} {/s}varispeeding {s} {ct}TV{/ct} {ss}Arbitrarily speeding and slowing of action.{/ss} {/s}VCR {s} {ss}Video Cassette Recorder.{/ss} {/s}vectograph {s} {ss}A photograph consisting of varying degrees of polarisation based on photographic content. Typically used to make stereoscopic photographs or slides that are viewed with special polarised glasses.{/ss} {/s}velocity field {s} {ct}video proc.{/ct} {ss}A vector representation of the velocity of image motion of many small regions of a time-varying image, produced by {sa}motion estimation{/sa}. Also known as motion field.{/ss} {/s}vergence (phoria) {s} {ct}biol., HVS{/ct} {ss}Degree to which the two eyes converge to fixate a target.{/ss} {/s}vernier acuity {s} {ss}The ability to judge whether two line segments are collinear.{/ss} {/s}VHS {s} {ss}Video Home System.{/ss} {/s}Vieth-Muller circle {s} {ss}When the foveal centres are pointed at an object, the range for which images of all other objects fall on corresponding points of zero horizontal disparity. This differs from the perceived range of zero disparity, the horopter.{/ss} {/s}vignette {s} {ct}image proc.{/ct} {ss}An image whose edges fade off softly into the background.{/ss} {/s}visible light {s} {ct}optics{/ct} {ss}The region of the electromagnetic spectrum in which the human retina is sensitive, ranging from about 400 to 750 nm in wavelength.{/ss} {/s}visual angle {s} {ss}A measurement of the area of the retina in degrees subtended by a stimulus. Roughly speaking the width of one's thumb at arm's length is approximately 2 degrees.{/ss} {/s}vitreous humor {s} {ct}biol.{/ct} {ss}Liquid filling the eye cavity.{/ss} {/s}volumetric display {s} {ct}3D, hw.{/ct} {ss}Type of 3D display. Usually involves rapidly sweeping out a cylindrical area and projecting light onto the surface.{/ss} {/s}VOP {s} {ct}standards{/ct} {ss}Video Object Plane. An MPEG-4 term describing an instance of a video object.{/ss} {/s}Voronoi diagram {s} {ct}math.{/ct} {ss}The Voronoi diagram of a collection of geometric objects is a partition of space into cells, each of which consists of the points closer to one particular object than to any others.{/ss} {/s}VPI {s} {ct}hw.{/ct} {ss}Visual Position Indicator, {sa}Sharp{/sa} in-house term for {sa}sweet spot indicator{/sa}.{/ss} {/s}Weber-Fechner function {s} {ss}Threshold versus intensity function.{/ss} {/s}Weber-Fechner theory {s} {ct}biol.{/ct} {ss}The intensity of a sensation is proportional to the logarithm of the strength of the stimulus. Used in perceptual coding.{/ss} {/s}well {s} {ct}image proc.{/ct} {ss}A morphological operator comprised of a closing followed by a subtraction of the output image from the original input image.{/ss} {/s}Wheatstone stereogram {s} {ct}3D{/ct} {ss}Fusing the two lines creates an image in depth with one line appearing to be above the other.{/ss} {/s}Wiener-Khintchine theorem {s} {ct}sig. proc.{/ct} {ss}For a stationary random process, the power spectral density is equivalent to the Fourier transform of the autocorrelation function.{/ss} {/s}window {s} {ct}image proc.{/ct} {ss}A selected portion of an image or a narrow range of pixel values.{/ss} {/s}windowing {s} {ct}image proc.{/ct} {ss}Performing imaging processing operations only within a predefined window or area in the image. {/ss} {/s}z keying {s} {ct}comp. graph., 3D{/ct} {ss}Inserting graphics between different depth layers in video.{/ss} {/s}ZDP {s} {ct}3D{/ct} {ss}See {sa}zero disparity plane{/sa}.{/ss} {/s}zero disparity plane {s} {ct}3D{/ct} {ss}Plane at which disparity between points in a stereo pair of images is zero.{/ss} {/s}