Glossary of Vision Terms - IVV-Inosys
Glossary of Vision Terms - IVV-Inosys
Glossary of Vision Terms - IVV-Inosys
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TERMS AND DEFINITIONS<br />
AGC - Automatic Gain Control. A circuit for automatically controlling amplifier gain in order to<br />
maintain a constant output voltage with a varying input voltage within a predetermined range <strong>of</strong><br />
input-to-output variation.<br />
Algorithm - A set <strong>of</strong> well-defined rules or procedures for solving a problem or providing an<br />
output from a specific set <strong>of</strong> inputs.<br />
Alpha Risk (ý-risk) - The risk <strong>of</strong> rejecting good product.<br />
Ambient light - Light that is present in the environment <strong>of</strong> the imaging front end <strong>of</strong> a vision<br />
system and generated from outside sources. This light is usually treated as background noise by<br />
the vision system. <strong>Vision</strong> cameras should be shielded from ambient light.<br />
Analog-to-Digital Converter (A/D) - A device that converts an analog signal to a discrete series<br />
<strong>of</strong> digitally encoded numbers (signal) for computer processing.<br />
Angle <strong>of</strong> View - The angular range that can be focused within the image size. Small focal lengths<br />
give a wide angle <strong>of</strong> view, and large focal lengths give a narrow field <strong>of</strong> view.<br />
Aperture - The opening <strong>of</strong> a lens which controls the amount <strong>of</strong> light reaching the surface <strong>of</strong> the<br />
pickup device. The size <strong>of</strong> the aperture is controlled by the iris adjustment. By increasing the f<br />
stop number (f1.4, f1.8, f2.8, etc.) less light is permitted to pass to the pickup device.<br />
Artifact - An artificially created structure (by accident or on purpose), form or shape, usually part<br />
<strong>of</strong> the background, used to assist in measurement or object location.<br />
Area Array Camera - A solid state imaging device with both rows and columns <strong>of</strong> pixels,<br />
forming an array which produces a 2D image.<br />
Aspect Ratio - The ratio <strong>of</strong> width to height for the frame <strong>of</strong> the televised picture. 4:3 (or 1.333)<br />
for standard systems, 5:4 for 1K x 1K.<br />
Asynchronous (frame reset) - A camera characteristic which allows the return to top-<strong>of</strong>-frame<br />
to occur on demand, rather than synchronously following the 60 Hz power line scanning<br />
frequency.<br />
Attenuation – A reduction in signal strength.<br />
Aut<strong>of</strong>ocus - The ability <strong>of</strong> an imaging system to control the focus <strong>of</strong> the lens to obtain the<br />
sharpest image on the detector. Edge crispness is a typical control variable.<br />
1
Auto Balance - A system for detecting errors in color balance in white and black areas <strong>of</strong> the<br />
picture and automatically adjusting the white and black levels <strong>of</strong> both the red and blue signals as<br />
needed for correction.<br />
Automatic Gain Control (AGC) - A process by which gain is automatically adjusted as a<br />
function <strong>of</strong> input or other specified parameter.<br />
Automatic Iris Lens - A lens in which the aperture automatically opens or closes to maintain<br />
proper light levels on the faceplate <strong>of</strong> the camera pickup device.<br />
Back Focal Distance - The distance from the rear most portion <strong>of</strong> the lens to the image plane.<br />
Backlighting - Placement <strong>of</strong> a light source behind an object so that a silhouette <strong>of</strong> that object is<br />
formed. It is used where outline information <strong>of</strong> the object and its features is important rather than<br />
surface features.<br />
Back Porch - That portion <strong>of</strong> the composite picture signal which lies between the trailing edge <strong>of</strong><br />
the horizontal sync pulse and the trailing edge <strong>of</strong> the corresponding blanking pulse.<br />
Bandwidth - The number <strong>of</strong> cycles per second (Hertz) expressing the difference between the<br />
lower and upper limiting frequencies <strong>of</strong> a frequency band; also, the width <strong>of</strong> a band <strong>of</strong> frequencies.<br />
Bar Code - An identification system that employs a series <strong>of</strong> machine-readable lines <strong>of</strong> varying<br />
widths <strong>of</strong> black and white.<br />
Bar Code (2D) - An arrangement <strong>of</strong> rectangles and spaces that contains far more information<br />
than a traditional bar code.<br />
Barrel Distortion - An optical imperfection that causes an image to bulge convexly on all sides<br />
similar to a barrel.<br />
Beamsplitter - An optical device which divides one beam into two or more separate beams. A<br />
simple coated piece <strong>of</strong> glass in the optical path might reflect 60% <strong>of</strong> the light down onto the<br />
object, while allowing the other 40% to pass.<br />
Beta Risk (-risk) - The risk <strong>of</strong> accepting bad or defective product.<br />
Binary image - A black and white image represented as a single bit containing either zeros or<br />
ones, in which objects appear as silhouettes. The result <strong>of</strong> backlighting or thresholding.<br />
Blob - A single, connected region in a binary or grayscale image.<br />
Blob Analysis - Identification <strong>of</strong> segmented objects in an image based on their geometric<br />
features.<br />
2
Borescope - A device for internal inspection <strong>of</strong> difficult access locations such as pipes, engines,<br />
rifle barrels and pipes. Its long narrow tube contains a telescope system with a number <strong>of</strong> relay<br />
lenses. Light is provided via the optical path or fiber bundles. A 45-degree mirror at the end<br />
allows inspection <strong>of</strong> tube walls.<br />
Blooming - The defocusing <strong>of</strong> regions <strong>of</strong> the picture where the brightness is at an excessive level.<br />
Calibration - The act <strong>of</strong> relating X and Y pixel spacing to a known or predetermined pixels per<br />
unit length (i.e. inch, mm) factor.<br />
Coatings - Light is lost by reflection from optical surfaces that are intended to be refractors only.<br />
Very thin coatings on the lens surfaces effectively reduce this loss. This can be seen as a blue or<br />
violet hue on the lens surface.<br />
C Mount - A television camera lens mount <strong>of</strong> the 16-mm format, 1 inch in diameter with 32<br />
threads per inch. CCTV lenses are available in two different lens mounts. "C-mount" lenses have a<br />
flange back distance <strong>of</strong> 17.5mm Vs 12.5mm for "CS-mount" lenses. Many <strong>of</strong> today's cameras can<br />
accept either type <strong>of</strong> lens, but it is important to make sure that camera and lens are compatible and<br />
set up properly. C-mount lenses can be used on CS-mount cameras by utilizing a 5mm adapter or<br />
adjusting the camera for C-mount lenses. Because <strong>of</strong> the shorter back focal distance, CS-mount<br />
lenses can only be used on CS-mount cameras. Your picture will be out <strong>of</strong> focus if you use a CSmount<br />
lens on a C-mount camera.<br />
CCTV - The abbreviation for Closed-Circuit Television.<br />
Centroid – In machine vision, this is the center <strong>of</strong> mass ( usually <strong>of</strong> the white pixel count ) or the<br />
center <strong>of</strong> location mark or fiducial.<br />
Character Recognition (OCR) - Imaging and recognizing individual characters in a scene. Also<br />
called Optical Character Recognition.<br />
Character Verification (OCV) - Imaging and verifying the correctness, quality and legibility <strong>of</strong><br />
known characters in an image. Also Optical Character Verification.<br />
Charge-Coupled Device (CCD) - For imaging devices, a self-scanning semiconductor array that<br />
utilizes MOS technology, surface storage, and information transfer by shift register techniques.<br />
Chroma - That qualities <strong>of</strong> color which embraces both hue and saturation. White, black, and<br />
grays have no chroma.<br />
Chroma Control - A control <strong>of</strong> color television receiver that regulates the saturation (vividness)<br />
<strong>of</strong> colors in a color picture.<br />
3
Chroma Detector - Detects the absence <strong>of</strong> chrominance information in a color encoder input.<br />
The chroma detector automatically deletes the color burst from the color encoder output when<br />
the absence <strong>of</strong> chrominance is detected.<br />
Chromatic Aberration - An optical defect <strong>of</strong> a lens which causes different colors or wave<br />
lengths <strong>of</strong> light to be focused at different distances from the lens. It is seen as color fringes or<br />
halos along edges and around every point in the image.<br />
Chromaticity - The color quality <strong>of</strong> light which is defined by the wavelength (hue) and<br />
saturation. Chromaticity defines all the qualities <strong>of</strong> color except its brightness.<br />
Chrominance - A color term defining the hue and saturation <strong>of</strong> a color. Does not refer to<br />
brightness.<br />
Chrominance Signal - The portion <strong>of</strong> the NTSC color television signal that contains the color<br />
information.<br />
Clamp - A device that functions during the horizontal blanking or synchronizing interval to fix<br />
the level <strong>of</strong> the picture signal at some predetermined reference level at the beginning <strong>of</strong> each<br />
scanning line.<br />
Clamping - The process that establishes a fixed level for the picture level at the beginning <strong>of</strong><br />
each scanning line.<br />
Clipping - The shearing <strong>of</strong>f <strong>of</strong> the peaks <strong>of</strong> a signal. For a picture signal, this effects the positive<br />
(white).<br />
Coaxial Cable - A particular type <strong>of</strong> cable capable <strong>of</strong> passing a wide range <strong>of</strong> frequencies with<br />
very low signal loss.<br />
Color Burst - That portion <strong>of</strong> the composite color signal, comprising a few cycles <strong>of</strong> a sine wave<br />
<strong>of</strong> chrominance subcarrier frequency, which is used to establish a reference for demodulating the<br />
chrominance signal.<br />
Color Camera – Color cameras use either a single chip sensor or a three-chip sensor to sense<br />
red, blue, and green.<br />
Color Edging - Extraneous colors appearing at the edges <strong>of</strong> colored objects, and differing from<br />
the true colors in the object.<br />
Color Encoder - A device which produces an NTSC color signal from separate R, G, and B<br />
video inputs.<br />
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Color Fringing - Spurious colors introduced into the picture by the change in position <strong>of</strong> the<br />
televised object from field to field.<br />
Color Purity - The degree to which a color is free <strong>of</strong> white or any other color.<br />
Color Saturation - The degree to which a color is free <strong>of</strong> white light.<br />
Color Sync Signal - A signal used to establish and to maintain the same color relationships that<br />
are transmitted.<br />
Color Transmission - The transmission <strong>of</strong> a signal that represents both the brightness values and<br />
the color values in a picture.<br />
Composite Video Signal - A camera signal that is produced by combining both a video or<br />
picture signal with horizontal and vertical synch and blanking, signals.<br />
Condenser Lens - Used to collect and redirect light for the purpose <strong>of</strong> illumination. Often used to<br />
collect light from a small source and project it evenly onto an object.<br />
Connectivity Analysis - A routine used to determine which pixels are interconnected and part <strong>of</strong><br />
the same object or region. The results are used for blob analysis.<br />
Contrast - The difference <strong>of</strong> light intensity between two adjacent regions in the image <strong>of</strong> an<br />
object. Often expressed as the difference between the lightest and darkest portion <strong>of</strong> an image.<br />
Contrast between a flaw (or a feature) and its background is the goal <strong>of</strong> illumination.<br />
Contrast Enhancement - Stretching <strong>of</strong> the gray level values between dark and light portions <strong>of</strong><br />
an image to improve both visibility and feature detection.<br />
Convergence - The crossover <strong>of</strong> the three electron beams <strong>of</strong> a three-gun tri-color picture tube.<br />
Convolution - Superimposing an m x n operator (usually a 3x3 or 5x5 mask) over an area <strong>of</strong> the<br />
image, multiplying the points together, summing the results to replace the original pixel with the<br />
new value. This operation can be performed on the entire image or regions <strong>of</strong> interests to enhance<br />
edges, features, remove noise and other filtering operations.<br />
Correlation - A mathematical measure <strong>of</strong> the similarity between images or areas within an image.<br />
Pattern matching, or correlation <strong>of</strong> an X by Y array size template to the same size image,<br />
produces a scalar number, the percentage <strong>of</strong> match. The template is usualy walked through a<br />
larger array to find the highest match.<br />
Crosstalk - An undesired signal from a different channel interfering with the desired signal.<br />
5
Darkfield Illumination - Lighting <strong>of</strong> objects, surfaces or particles at very shallow or low angles,<br />
so that light does not directly enter the optics. Objects are bright with a dark background. This<br />
grazing illumination causes specular reflections from abrupt surface irregularities.<br />
DC Type Lens - An auto-iris lens with an internal circuit which receives voltage and a video<br />
signal from the camera to adjust the iris.<br />
.<br />
Depth <strong>of</strong> Field - The front to back zone in a field <strong>of</strong> view that is in focus in the televised scene.<br />
With a greater depth <strong>of</strong> field, more <strong>of</strong> the scene, near to far, is in focus. Increasing the f-stop<br />
number increases the depth <strong>of</strong> field <strong>of</strong> the lens. Therefore, the lens aperture should be set at the<br />
highest f-stop number usable with the available lighting. The better the lighting, the greater the<br />
depth <strong>of</strong> field possible. In other words, the depth <strong>of</strong> field is the area in front <strong>of</strong> the camera that<br />
remains in focus. The larger the f-number the greater is the depth <strong>of</strong> field.<br />
Depth <strong>of</strong> Focus - The range <strong>of</strong> sensor-to-lens distance for which the image formed by the lens is<br />
clearly focused.<br />
Diffused lighting - Scattered s<strong>of</strong>t lighting from a wide variety <strong>of</strong> angles used to eliminate<br />
shadows and specular glints from pr<strong>of</strong>iled, highly reflective surfaces. Diffused lighting minimizes<br />
surface texture.<br />
Digital Area Scan Cameras - These cameras have an on board analog to digital converter that<br />
converts the light level <strong>of</strong> each pixel on the CCD array into a digital word. The advantages to<br />
digital cameras are that the image data can be transmitted quicker, without degradation, and are<br />
less susceptible to noise.<br />
Digital Line Scan Cameras - These cameras have an on board analog to digital converter that<br />
converts the light level <strong>of</strong> a single line (row) <strong>of</strong> pixels into a digital word. They send the data out<br />
one line at a time. These cameras are high-resolution cameras capable <strong>of</strong> very high data rates.<br />
Linescan cameras require a very intense light and an encoder to track the part while it is moving<br />
under the camera.<br />
Distortion - The deviation <strong>of</strong> the received signal waveform from that <strong>of</strong> the original transmitted<br />
waveform.<br />
Dynamic Range - The difference between the maximum acceptable signal level and the minimum<br />
acceptable signal level.<br />
Edge - A change in pixel values exceeding some threshold amount. Edges represent borders<br />
between regions on an object or in a scene.<br />
Edge Detection - The ability to determine the true edge <strong>of</strong> an object.<br />
6
EIA Sync - The signal used for the synchronizing <strong>of</strong> scanning specified in EIA Standards RS-<br />
170, RS-330, RS-343, or subsequent issues.<br />
Extension Tube - A kit consisting <strong>of</strong> various size spacers that are used between the lens and the<br />
camera to reduce the lens minimum object distance. Extension tubes are not recommended for<br />
zoom lenses due to loss <strong>of</strong> tracking.<br />
Feature Extraction - Determining image features by applying feature detectors to distinguish or<br />
segment them from the background.<br />
Fiber Optics - Transparent fibers all bundled together parallel to one another. This bundle <strong>of</strong><br />
fibers has the ability to transmit a light from one <strong>of</strong> its surfaces to the other around curves and<br />
into otherwise inaccessible places with an extremely low loss <strong>of</strong> definition and light.<br />
Fiberscope - An optical instrument similar to a borescope, but uses a flexible, coherent fiber or<br />
bundle (usually silicon), an objective lens and an eyepiece or camera.<br />
Fiducial - A line, mark or shape used as a standard <strong>of</strong> reference for measurement or location.<br />
Field - One <strong>of</strong> two parts <strong>of</strong> a video frame in an interlaced scanning system. One even field and<br />
one odd field compromise one video frame.<br />
Field <strong>of</strong> View - The maximum angle <strong>of</strong> view that can be seen through a lens or optical<br />
instrument.<br />
F-Number - The f-number indicates the brightness <strong>of</strong> the image formed by lens, controlled by the<br />
iris. A smaller f-number means a brighter image.<br />
Focal Length - The distance from the center <strong>of</strong> the lens to a plane at which point a sharp image<br />
<strong>of</strong> an object viewed at an infinite distance from the camera is produced. The focal length<br />
determines the size <strong>of</strong> the image and the angle <strong>of</strong> the field <strong>of</strong> view seen by the camera through the<br />
lens. That is the distance from the center <strong>of</strong> the lens to the pickup device.<br />
Frame - The total area (2 fields on an RS-170 signal) that is scanned while the camera signal is<br />
not blanked.<br />
Frame Frequency - The number <strong>of</strong> times per second that the frame is scanned. The U.S.<br />
standard is 30 frames per second.<br />
Frame Buffer - Image memory in a frame grabber.<br />
Frame Grabber - A device that interfaces with a camera and, on command, samples the video,<br />
converts the sample to a digital value and stores that number in a computer's memory.<br />
7
Frame Transfer - A CCD imager where an entire matrix <strong>of</strong> pixels is read into storage before<br />
being output from the camera.<br />
Frequency Interlace - The method by which color and black and white sideband signals are<br />
interwoven within the same channel bandwidth.<br />
Front Lighting - The use <strong>of</strong> illumination on the camera side <strong>of</strong> an object so that the surface<br />
features can be observed.<br />
Front Porch - The portion <strong>of</strong> a composite picture signal that lies between the leading edge <strong>of</strong> the<br />
horizontal blanking pulse and the leading edge <strong>of</strong> the corresponding sync pulse.<br />
F/Stop - A term used to indicate the speed <strong>of</strong> a lens. The smaller the f-number, the greater the<br />
amount <strong>of</strong> light passing through the lens.<br />
Gauging - In machine vision, non-contact dimensional examination <strong>of</strong> an object.<br />
Gain - An increase in voltage or power, usually expressed in dB.<br />
Gamma - A numerical value, or the degree <strong>of</strong> contrast in a television picture, which is the<br />
exponent <strong>of</strong> that power law which is used to approximate the curve <strong>of</strong> output magnitude versus<br />
input magnitude over the region <strong>of</strong> interest.<br />
Gamma Correction - To provide for a linear transfer characteristic from input to output device.<br />
Genlock - A device used to lock the frequency <strong>of</strong> an internal sync generator to an external<br />
source.<br />
Ghost - A spurious image resulting from an echo.<br />
Gray Scale - Variations in value from white, through shades <strong>of</strong> gray, to black (usually 256, 8 -bit<br />
image) on a television screen. The gradations approximate the tonal values <strong>of</strong> the original image<br />
picked up by the machine vision camera.<br />
Hue - Corresponds to colors such as red, blue, etceteras.<br />
Image Intensifier - A device coupled by fiber optics to a camera image pickup sensor to increase<br />
sensitivity.<br />
Impedance (input or output) - The input or output characteristic <strong>of</strong> a system component that<br />
determines the type <strong>of</strong> transmission cable to be used. The cable used must have the same<br />
characteristic impedance as the component. Expressed in ohms. Video distribution has<br />
standardized on 75-ohm coaxial and 124-ohm balanced cable.<br />
8
Incident Light - The light that falls directly on an object.<br />
Interline Transfer - A technology <strong>of</strong> CCD design, where rows <strong>of</strong> pixels are output from the<br />
camera. The sensor's active pixel area and storage register are both contained within the active<br />
image area.<br />
Interlaced Scanning - A scanning process in which all-odd lines then all even lines are<br />
alternately scanned. Adjacent lines belong to different fields and are collected at different times.<br />
So, a moving object may appear in a slightly different location on odd/even fields.<br />
Iris - An adjustable aperture built into a camera lens to permit control <strong>of</strong> the amount <strong>of</strong> light<br />
passing through the lens.<br />
Jitter - Small, rapid variations in a waveform due to mechanical disturbances or to changes in the<br />
characteristic <strong>of</strong> components. Supply voltages, imperfect synchronizing signals, circuits, etc.<br />
Lens Preset Positioning - Follower Pots are installed on lens that allows feedback to the<br />
controller information relevant to zoom and focus positioning allowing the controller to quickly<br />
adjust to a preselected scene and arrive in focus at the proper focal length automatically.<br />
Lens Speed - Refers to the ability <strong>of</strong> a lens to transmit light, represented as the ratio <strong>of</strong> the focal<br />
length to the diameter <strong>of</strong> the lens. A fast lens would be rated f/8. The larger the f number, the slower the lens.<br />
Level Control - Main iris control. Used to set the auto-iris circuit to a video level desired by the<br />
user. After set-up, the circuit will adjust the iris to maintain this video level desired by the user.<br />
After set-up, the circuit will adjust the iris to maintain this video level in changing lighting<br />
conditions.<br />
Light - Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400<br />
to 750 nm.<br />
Line Scan Camera - A solid state video camera consisting <strong>of</strong> a single row <strong>of</strong> pixels. The sensor<br />
captures a row <strong>of</strong> data, reads it out, then captures the next row <strong>of</strong> data.<br />
Loss - A reduction in signal level or strength, usually expressed in dB. Power dissipation serving<br />
no useful purpose.<br />
Low-Frequency Distortion - Distortion effects which occur at low frequencies. In television,<br />
generally considered as any frequency below the 15.75-kHz line frequency.<br />
Lumen (LM) - The unit <strong>of</strong> luminous flux.<br />
9
Lumen/FT2 - A unit <strong>of</strong> incident light. It is the illumination on a surface one square foot in area<br />
on which a flux <strong>of</strong> one lumen is uniformly distributed, or the illumination at a surface all points <strong>of</strong><br />
which are at a distance <strong>of</strong> one foot from a uniform source <strong>of</strong> one candela.<br />
Luminance Signal - That portion <strong>of</strong> the NTSC color television signal which contains the<br />
luminance or brightness information.<br />
Lux - International System (Sl) unit <strong>of</strong> illumination in which the meter is the unit <strong>of</strong> length. One<br />
lux equals one lumen per square meter.<br />
Machine <strong>Vision</strong> - The use <strong>of</strong> devices for optical non-contact sensing to automatically receive and<br />
interpret an image <strong>of</strong> a real scene, in order to obtain information and/or control machines or<br />
processes.<br />
Manual Iris Lens - A lens with a manual adjustment to set the iris opening (F-stop) in a fixed<br />
position.<br />
.<br />
Minimum Object Distance (M.O.D.) - The closest distance a given lens will be able to focus<br />
upon an object. This is measured from the vertex (front) <strong>of</strong> the lens to the object. Wide-angle<br />
lenses generally have a smaller M.O.D. than large focal length lenses.<br />
Modulation - The process, or results <strong>of</strong> the process, whereby some characteristic <strong>of</strong> one signal is<br />
varied in accordance with another signal. The modulated signal is called the carrier. The carrier<br />
may be modulated in three fundamental ways: by varying the amplitude, called amplitude<br />
modulation; by varying the frequency, called frequency modulation; by varying the phase, called<br />
phase modulation.<br />
Monochrome - A gray scale image.<br />
Morphology - Image algebra group <strong>of</strong> mathematical operations based on manipulation and<br />
recognition <strong>of</strong> shapes. Also called mathematical morphology. Operations may be performed on<br />
either binary or gray scale images.<br />
Opaqueness - The degree to which an object does not transmit light.<br />
ND Filter - A filter that attenuates light evenly over the visible light spectrum. It reduces the<br />
light entering a lens, thus forcing the iris to open to its maximum.<br />
Noise - The word "noise" originated in audio practice and refers to random spurts <strong>of</strong> electrical<br />
energy or interference. In some cases, it will produce a "salt-and-pepper" pattern over the<br />
televised picture. Heavy noise is sometimes referred to as "snow".<br />
Non-Composite Video - A video signal containing all information except sync.<br />
10
Non-Interlaced Scan (sequential scan) - The camera begins at the start <strong>of</strong> the frame and lines<br />
are scanned in their natural order (1,2,3,4…. etc.).<br />
NTSC - Abbreviation for National Television Systems Committee. A committee that worked<br />
with the FCC in formulating standards for the present day United States color television system.<br />
Pan and Tilt - A device upon which a camera can be mounted that allows movement in both the<br />
azimuth (pan) and in the vertical plane (tilt).<br />
Pan/Tilt Preset Positioning - Follower pots are installed on pan/tilt unit to allow feedback to the<br />
controller and provides information relevant to horizontal and vertical positioning, allowing the<br />
controller to quickly adjust to a pre-selected scene automatically.<br />
Pattern Recognition - A process that identifies an object based on analysis <strong>of</strong> its features.<br />
Peak-to-Peak - The amplitude (voltage) difference between the most positive and the most<br />
negative excursions (peaks) <strong>of</strong> an electrical signal. A full video signal measures one-volt peak to<br />
peak.<br />
Pinhole Lens - Lens which uses a very small pinhole instead <strong>of</strong> a glass lens. These lenses are<br />
generally used in higher light situations and are inherently “in focus” at all working distances.<br />
Pixel - Short for Picture Element. A pixel is the smallest area <strong>of</strong> a television picture capable <strong>of</strong><br />
being delineated by an electrical signal passed through the vision system. The number <strong>of</strong> picture<br />
elements (pixels) in a complete picture, and their geometric characteristics <strong>of</strong> vertical height and<br />
horizontal width, provides information on the total amount <strong>of</strong> detail that the can be displayed.<br />
Polarizer - An optical device that converts natural or unpolarized light into polarized light by<br />
selective absorption <strong>of</strong> rays in one direction, and passing <strong>of</strong> rays perpendicular to the polarizing<br />
medium.<br />
Pre-Position Lenses - Zoom lenses that utilize a variable-resistor (potentiometer) to indicate<br />
zoom/focus position to the lens controller. After initial set-up, this allows the operator to view<br />
different pre-set areas quickly without having to readjust the zoom and focus each time.<br />
Primary Colors - The colors wherein no mixture <strong>of</strong> any two can produce the third. In color<br />
television these are the additive primary colors red, blue and green.<br />
Progressive Scan - The progressive scan format outputs data from the camera (the signal) in<br />
sequential order as it is scanned. The scan format produces a full frame <strong>of</strong> video in a continuous<br />
stream, rather than half the image per output sequence(interlaced image) in traditional RS-170<br />
CCD cameras. Standard RS-170 video is interlaced and output in two separate fields, generating<br />
essentially half the image at a time.<br />
11
Real Time Processing - In machine vision, the ability <strong>of</strong> a system to perform a complete analysis<br />
and take action on one part before the next one arrives for inspection.<br />
Resolution (horizontal) - The amount <strong>of</strong> resolvable detail (vertical rows <strong>of</strong> pixels) in the<br />
horizontal direction in an image.<br />
Resolution (vertical) - The amount <strong>of</strong> resolvable detail (horizontal lines <strong>of</strong> pixels) in the vertical<br />
direction in an image.<br />
Roll - A loss <strong>of</strong> vertical synchronization that causes the picture to move up or down on a receiver<br />
or monitor.<br />
RS-170 - The Electronic Industries Association (EIA) standard governing monochrome television<br />
studio electrical signals. The broadcast standard <strong>of</strong> 30 complete images per second.<br />
RS-232-C - The Electronic Industries Association (EIA) standard governing serial<br />
communications over a twisted pair. Good to about 150 feet.<br />
RS-330 - Standard governing color television studio electrical signals.<br />
RS-422; RS-423; RS-449 - The Electronic Industries Association (EIA) standards for serial<br />
communication protocols intended to gradually replace the widely used RS-232-C standard.<br />
Saturation - The degree to which a color is diluted with white light or is pure. The vividness <strong>of</strong> a<br />
color, described by such terms as bright, deep, pastel, pale, etc. Saturation is directly related to<br />
the amplitude <strong>of</strong> the chrominance signal.<br />
Sensitivity - In television, a factor expressing the incident illumination upon a specified scene<br />
required to produce a specified picture signal at the output terminals <strong>of</strong> a television camera.<br />
Shutter - Ability to control the integration time to the image sensor too less than 1/60 second;<br />
e.g.: stop motion <strong>of</strong> moving traffic.<br />
Signal-to-Noise Ratio - The ratio between useful television signal and disturbing noise or snow.<br />
Snow - Heavy random noise.<br />
Specular Reflections – Light rays come from a single direction and are bright. They are<br />
unreliable because a small change in angle between the illuminator and the object may cause the<br />
specular reflection to disappear.<br />
Standard Minimum Signal - 1000 microvolts at 75 ohms (0dB mV) in RF systems; 0.7-VPP<br />
non-composite, 1-VPP composite in video systems.<br />
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Strobe Duration - The amount <strong>of</strong> time, expressed in microseconds, during which the flash lamp<br />
(strobe) is at 90% intensity.<br />
Strobe Light - Brief flashes <strong>of</strong> light for observing an object during a short interval <strong>of</strong> time,<br />
typically used to "stop" movement and resulting image blur. Strobes may use xenon flash tubes,<br />
banks <strong>of</strong> LED’s or a laser to illuminate the scene.<br />
Structured Light - Points, lines, circles, sheets and other projected configurations used to<br />
directly determine shape and/or range information by observing their deformation as it intersects<br />
the object in a known geometric configuration.<br />
Subpixel Resolution - Mathematical techniques used on gray scale images to resolve an edge<br />
location too less than one pixel.<br />
Sync Generator - A device for generating a synchronizing signal.<br />
Sync Signal - The signal employed for the synchronizing <strong>of</strong> scanning.<br />
Tearing - A term used to describe a picture condition in which groups <strong>of</strong> horizontal lines are<br />
displaced in an irregular manner.<br />
Telecentric Lens – A lens that provides constant magnification at any object distance. They make<br />
accurate dimensional measurements over a larger range than conventional lens. Also, telecentric<br />
lenses view the whole field form the same perspective. Thus, a deep round hole looks round at the<br />
top and bottom <strong>of</strong> the hole.<br />
Template Matching - A form <strong>of</strong> correlation used to find out how well two images match.<br />
Thresholding - The process <strong>of</strong> converting gray scale image into a binary image. If the pixel's<br />
value is above the threshold, it is converted to white. If below the threshold, the pixel value is<br />
converted to black.<br />
Throughput Rate - The maximum parts per minute inspection rate <strong>of</strong> a system.<br />
Tracking - The ability <strong>of</strong> a zoom lens to remain in focus during the entire zoom range from wide<br />
angle to telephoto position.<br />
Variable Scan Camera - This is a non RS-170 camera that sends out sync and clock signals to<br />
the frame grabber that allows for the camera scan rate to vary.<br />
Video Band - The frequency band width utilized to transmit a composite video signal.<br />
Video Signal (Non-Composite) - The picture signal. A signal containing visual information and<br />
horizontal and vertical blanking (see also Composite Video Signal) but not sync.<br />
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Xenon Strobe - A gas filled electronic discharge tube, useful for high speed, short duration<br />
illumination for inspection.<br />
Y Signal - A signal transmitted in color television containing brightness information. This signal<br />
produces a black and white picture on a standard monochrome receiver. In a color picture it<br />
supplies fine detail and brightness information.<br />
Zoom Lens - A lens system that may be effectively used as a wide angle, standard, or telephoto<br />
lens by varying the focal length <strong>of</strong> the lens.<br />
Zoom Ratio - The ratio <strong>of</strong> the starting focal length (wide position) to the ending focal length<br />
(telephoto position) <strong>of</strong> a zoom lens. A lens with a 10X-zoom ratio will magnify the image at the<br />
wide-angle end by 10 times.<br />
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