Glossary of Terms:
Imaging Solutions

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Aberration
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.

Absorption
The loss of light of certain wavelengths as it passes through a material and is converted to heat or other forms of energy.

Accuracy
The extent to which a machine vision system can correctly measure or obtain a true value of a feature. The closeness of the average value of the measurements to the actual dimension.

Ambient Light
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.

Aspect Ratio
The ratio of the width to the height of a frame of a video image. The U.S. television standard is 4:3 or 1.333.

Auto focus
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.

Automation
The degree to which activities of machines or production systems are self-acting.

B

Backlighting
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.

Bandpass Filter
An absorbing filter which allows a known range of wavelengths to pass, blocking those of lower or higher frequency.

Barrel Distortion
An optical imperfection which causes an image to bulge convexly on all sides similar to a barrel.

Beamsplitter
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.

Bonding (Bonded)
The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to safely conduct any current likely to be imposed.

Borescope
A device for internal inspection of difficult access locations such as, engines, rifle barrels and pipes. Its long narrow tube contains a telescope system with a number of relay lenses. Light is provided via the optical path or fiber bundles. A 45 degree mirror at the end allows inspection of tube walls.

Brightness
The total amount of light or incident illumination on a scene or object per unit area. Also called intensity.

C

C-mount
A threaded means of mounting a lens to a camera. A C-mount camera has a 17.5 mm distance from the camera sensor to the edge of the threads ("face to sensor").

CS-mount
A threaded means of mounting a lens to a camera. A CS-mount camera has a 12.5 mm distance from the camera sensor to the edge of the threads ("face to sensor"). The thread size and pitch of a CS-mount camera are identical to that of a C-mount camera, however the 5 mm difference will not allow the lens to work as it was designed. Many cameras are both C-mount and CS-mount compatible. This usually means that a 5 mm spacer ring is supplied to increase the "face to sensor" distance to 17.5 mm, making it a C-mount camera.

Calibration
A measurement or comparison against a standard. Or, the determination of any equipment deviation from a standard source so as to ascertain the proper correction factors.

CCD
Charge Coupled Device. A photo-sensitive image sensor implemented with large scale integration technology.

Centration
In a lens, a measure of the angular deviation of the optical axis. It is defined by a line through the centers of curvature of the optical surfaces, and the mechanical axis, defined by the ground outside diameter of the lens.

Cleanroom
A confined area in which the humidity, temperature, particle matter, and contamination are precisely controlled within specified parameters.

Coaxial Illumination
Front lighting with the illumination path running along the imaging optical axis and usually introduced with a 45 degree angle beam splitter.

Collimate
To produce light with parallel rays.

Collimated Lighting
Radiation from a given point with every light ray considered parallel. In actuality, even light from a very distant point source (ie a star) diverges somewhat. Note that all collimators have some aberrations.

Component
An individual piece or a complete assembly of individual pieces, including industrial products that are manufactured as independent units, capable of being joined together with other pieces or components.

Condenser Lens
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.

Contrast
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.

Correlation
A process whereby two image segments are compared to determine their similarity or to find the position at which optimal similarity exists.

Cross Section
A 3-D profile of a slice of an object.

Cycle
One complete operational sequence (including unit load and unload) of processing, manufacturing, or testing steps for an equipment system or subsystem.

D

Daisy Chained
Connected so that the removal of one component causes the interruption of the circuit to another component.

Darkfield Illumination
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.

Defect
Flaw or imperfection. Any unintentional and undesirable irregularity in the part surface that could affect system performance. Examples of such defects include cracks, inclusions, blistering, dents, pits, stringers and scratches.

Depth of Field
The range of an imaging system in which objects are in focus. Measured from the distance behind an object to the distance in front of the object with all objects appearing in focus.

Depth Perception
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.

Die
A field sub-unit. An area of substrate that contains the device being manufactured.

Diffused Lighting
Scattered soft lighting from a wide variety of angles used to eliminate shadows and specular glints from profiled, highly reflective surfaces.

Diffraction
A fundamental and inescapable physical phenomenon where, in all light beams, some energy is spread outside the region predicted by rectilinear propagation.

Diopter
A term used to define the reciprocal focal length, commonly used for ophthalmic lenses. The inverse focal length of a lens expressed in diopters is 1000/f, where f is the focal length in millimeters.

Dispersion
Separation of a beam of light into its wavelength components, each of which travel at slightly different speeds. Also called chromatic dispersion.

Distortion
A change in magnification with the distance of an object from the optical axis. This can effect the accuracy of measuring the size of an object.

Downtime
A time when the equipment is not in a condition, or is not available, to perform its intended function. It does not include any portion of non-scheduled time.

E

Edge
A change in pixel values exceeding some threshold amount. Edges represent borders between regions on an object or in a scene.

Edge Detection
The ability to determine the edge of an object.

E-diagnostic
Electronic access to equipment for the purpose of diagnosing problems from a distance.

Electro-magnetic Spectrum
The total range of wavelengths, extending from the longest (audio) to the shortest (gamma rays) which can be physically generated. This entire spectrum is potentially useful for imaging, well beyond just the visible spectrum.

Encoder (Shaft or position)
Provides rotation information for control of image acquisition, especially for moving web processes. Outputs either pulses for counting or BCD parallel with absolute position information.

Exit Pupil
The virtual image of the exit aperture as seen from the image side.

Extension Tube
A cylindrical threaded tube used to change the magnification, effective focal length and field of view of a lens when inserted between the lens and imaging sensor.

F

F-number or f-stop
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.

Fiber Optics
Light source or optical image delivery via a long, flexible fiber(s) of transparent material, usually bundled together. Light is transmitted via internal reflection inside each fiber. Coherent fiber optics are spatially organized so images can be relayed.

Fiberscope
An optical instrument similar to a borescope, but uses a flexible, coherent fiber or bundle (usually silicon), an objective lens and an eyepiece or camera.

Field of View (FOV)
The two dimensional area which can be seen through the optical imaging system. In the case of a zoom optical system, you have a varying field of view. At the highest magnification, you have a smaller field of view. At the lowest magnification, you have the largest field of view.

Filter
A device or process that selectively transmits frequencies. In optics, the material either reflects or absorbs certain wavelengths of light, while passing others.

Flatness
The allowable deviation of a surface from a reference plane. The tolerance zone is defined by two parallel planes within which the surface must lie.

Fluorescence
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.

Focal Length
The distance from a lens' principal point to the corresponding focal point on the object.

Focal Plane
Usually found at the image sensor, it is a plane perpendicular to the lens axis at the point of focus.

Focus
The point at which rays of light converge for any given point on the object in the image. Also called the focal point.

Footprint
The total area or floor space consumed by a piece of equipment when viewed perpendicular to the area of reference. (Normally, when viewed from directly overhead and considering the floor.)

Front End System
The object, illumination, optics and imager blocks of a vision system. Includes all components useful to acquire a good image for subsequent processing.

Front Lighting
The use of illumination on the camera side of an object so that surface features can be observed.

G

Gauging
In machine vision, non-contact dimensional examination of an object.

Ghost Image
A faint image caused by reflections at uncoated or antireflection-coated surfaces.

GUI
An acronym for Graphical User Interface. Pronounced "gooie." A Windows based user interface screen or series of screens allowing the user to point-and-click to select icons rather than typing commands.

H

High Pass Filter
Passes detailed high frequency image information, while attenuating low frequency, slow changing data.

High Speed Imaging
Image capture near, at or above 1800 parts per minute (30 parts per second).

Hz
An abbreviation for Hertz or cycles per second. Often used with metric prefixes such as kHz or MHz for kilohertz and megahertz respectively.

I

Illumination
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.

Image
Projection of an object or scene onto a plane (i.e. screen or image sensor).

Image Capture
The process of acquiring an image of a part or scene, from sensor irradiation to acquisition of a digital image.

Image Distortion
A situation in which the image is not exactly true to scale with the object scale.

Image Plane
The plane surface of the imaging sensor, perpendicular to the viewing direction, at which the optics are focused.

Incident Light
Light which falls directly onto an object.

Infrared
The region of the electromagnetic spectrum adjacent to the visible spectrum, just beyond red with longer wavelengths (between 700nm and 3000nm).

Inspection
Non-destructive examination of a work piece to verify conformance to some criteria.

Intensity
The relative brightness of a portion of the image or illumination source.

L

Laser Illumination
Lighting an object with a laser source for frequency selection, pulse width (strobe) control or for accurate positioning.

LED
Light Emitting Diode. Often used as a strobe for medium speed objects.

Lens
A transparent piece of material, usually glass or plastic, with curved surfaces which either converge or diverge light rays. Often used in groups for light control and focusing.

Lens Speed
Also known as the f-number, it is the ratio of the focal length of the lens to its clear aperture.

Lifecycle
The entire life of an item of equipment, from conceptual design through to disposal.

Lighting
See illumination.

Limit
The level of susceptibility that a stated standard allows.

Line Scan Camera
A solid state video camera consisting of a single row of pixels. Also called a linear array camera.

Low Pass Filter
A digital or optical filter which passes slow changing, low frequency information, while attenuating high frequency, detailed edge information.

M

Machine Vision
The automatic acquisition and analysis of images to obtain desired data for controlling a specific activity.

Machine Vision System
A system capable of acquiring one or more images using an optical non-contact sensing device capable of processing, analyzing and measuring various characteristics so decisions can be made.

Magnification
The relationship between the length of a line or size of a feature in the object plane with the length or size of the same in the image plane. (The ratio of the image size to the object size.)

Manual Operation
Defined as any control outside of automated operation.

Material Handling
Hardware systems that provide motion, indexing and/or orientation both during manufacture and the inspection process.

Measurement
Verification that a work piece conforms to specified tolerances, such as dimensions, colors or textures. The process of assigning a value to an object.

Micron
One millionth of a meter also called a micrometer.

Mirror
A smooth, highly polished surface, for reflecting light. It may be plane or curved. Mirrors are fabricated by depositing a thin coating of silver or aluminum on a glass substrate. First surface mirrors are coated on the top surface, thus avoiding a second ghost image produced when light is reflected off the back surface after passing through the glass twice.

Modulation Transfer Function (MTF)
The ability of a lens or optical system to reproduce (transfer) various levels of detail (modulation) of an object to the image as the frequency (usually sinusoidal) increases.

MOS Array
Metal Oxide Semiconductor camera array sensor with random addressing capability, rows and columns of photodiodes and charge sent directly from the photodiode to the camera output.

N

Near Infrared
The region of the electromagnetic spectrum ranging from 700nm to approximately 3 microns.

Noise
Irrelevant or meaningless data resulting from various causes unrelated to the source. Random, undesired video signals.

Numerical Aperture (N.A.)
The product of the angle formed by the cone of on-axis rays and the index of refraction of the medium in which the cone resides. With higher numerical aperture, more light will be collected. In a diffraction limited system, the numerical aperture is directly proportional to the resolution of the optical system.

O

Object
The 3-D item to be imaged, gauged or inspected.

Object Plane
An imaginary plane at the object, which is focused by the optical system at the image plane on the sensor.

OEM
Original Equipment Manufacturer that supplies components to another for resale.

Off-the-Shelf
Refers to a general purpose system, readily available for immediate shipment, which is not configured for a specific application.

Opaqueness
Degree to which an object does not transmit light.

P

Pattern Recognition
A process which identifies an object based on analysis of its features.

Photodiode
A single photoelectric sensor element, either used stand-alone or a pixel site, part of a larger sensor array.

Photometry
Measurement of light which is visible to the human eye.

Pixel
An acronym for "picture element." The smallest distinguishable and resolvable area in an image. The discrete location of an individual photo-sensor in a solid state camera.

Polarized Light
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 at 90 degrees, polarizers theoretically blocks all light transmission.

Polarizer
An optical device which converts natural or unpolarized light into polarized light by selective absorption of rays in one direction, and passing of rays perpendicular to the polarizing medium. Usually fabricated from stretched plastic sheets with oriented, parallel birefringent crystals. The first polarizers were constructed with parallel wires.

Precision
The degree of spread or deviation between each measurement of the same part or feature. Repeatability.

R

Random Access
The ability to read out chosen lines or windows of information from an imager as needed, without following the RS-170 standards.

Real Time Processing
In machine vision, the ability of a system to perform a complete analysis and take action on one part before the next one arrives for inspection.

Reflection
The process by which incident light leaves the surface from the same side as it is illuminated.

Refraction
The bending of light rays as they pass from one medium (i.e. air) to another (i.e. glass), each with a different index of refraction.

Region
Area of an image. Also called a region of interest for image processing operations.

Repeatability
The ability of a system to reproduce or duplicate the same measurement. The total range of variation of a dimension is called the 6-sigma repeatability.

Resolution
The act or result of displaying fine detail in an image. The limit of resolution in the minimum separation between alternating black and white line pairs. Resolution is often given in the units of line pairs per mm (lp/mm) or in minimum resolvable spot size.

Resolution, Image
The number of rows and columns of pixels in an image.

Resolution, Feature
The smallest object or feature in an image which may be sensed.

Resolution, Measurement
The smallest movement measurable by a vision system.

Reticle
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.

Ringlight
A circular lamp or bundles of optical fibers arranged around the perimeter of an objective lens to illuminate the object in the field below it.

S

Scattering
Redirection of light reflecting off a surface or through an object. See diffuse.

Shading
The variation of the brightness or relative illumination over the surface of an object, often caused by color variations or surface curvature.

Smart Camera
A new term for a complete vision system contained in the camera body itself, including imaging, image processing and decision making functions.

Solid-State Camera
A camera which uses a solid state integrated circuit chip to convert incident light or other radiation into an analog electrical signal.

Sorting
Real and virtual separation of test specimens in different categories specified by one or multiple parameters.

Subassembly
A component of equipment that performs some limited functionality.

Sub-component
A component that is fully contained within a larger component. The interfaces of the sub-component may be hidden or exposed by the encapsulating component.

Substrate
The basic unit of material on which work is performed to create a product. Examples include wafers, die, plates used for masks, flat panels, circuit boards, lead frames, CDs and disks.

Systems Integration
The art of assembling hardware, software, components, mounts and enclosures to produce a system that meets a customer's specification.

T

Telecentric Lens
A lens in which the aperture stop is located at the front focus, resulting in the chief rays being parallel to the optical axis in image space (i.e. the exit pupil is at infinity). This results in the apparent size of the object not changing with focus. A true telecentric lens maintains a constant viewing angle at any point across the clear aperture of the objective lens allowing the machine vision system to generate dimensionally accurate images for measurement.

Telephoto Lens
A camera lens system designed to give a large image of a distant object. In general, a compound lens system wherein the effective focal length of the lens system is greater than the overall length of the system.

Throughput Rate
The number of units of production that pass through a process per period of time.

Threshold
The level set on a scanning surface inspection system (SSIS) to discriminate between pulses of different sizes. Or, when creating a binary image having only two intensity levels (black and white) from an original grayscale digital image that has 256 possible intensity values (for an 8-bit image), a binary threshold level must be chosen to designate the intensity level at which binary segregation occurs.

Tolerance
The absolute magnitude of the range of the product specification. Tolerance is sometimes given in terms of the deviation from the mean.

Transmittance
The ratio of the radiant power transmitted by an optical element or object to the incident radiant power. (The percentage of incident light which permeates the glass.) It is effected by material composition, temperature, thickness and light wavelength.

U

Ultraviolet
The region of the electromagnetic spectrum adjacent to the visible spectrum, but of higher frequency (shorter wavelength) than blue ranging from 200 to 400 nm. UV A ranges from 320 to 400 nm while UV B falls between 280 and 320 nm.

V

Verification
Activity providing qualitative assurance that a fabrication or assembly process was successfully completed.

Vignetting
The gradual reduction of image illuminance as the field size increases. Vignetting results from limitations of the clear apertures of the elements within the optical system.

Visible Light
The region of the electromagnetic spectrum in which the human retina is sensitive, ranging from about 400 to 700 nm in wavelength.

W

Wafer
Semiconductor substrate upon which multiple die are fabricated.

Wavelength
A term used to describe the electromagnetic waves which is light. The visible spectrum is 400 to 700nm. The near infrared spectrum is 700 to 3000nm. Materials exhibit different characteristics at different wavelengths of light.

Working Distance (W.D.)
The distance from the specimen to the bottom-most mechanical component of the optical system.

Workspace
The available area where the user is expected to operate, maintain, and service the equipment.

X

X-ray
A portion of the electromagnetic spectrum beyond the ultraviolet with higher frequency and shorter wavelengths. Able to penetrate solid objects for internal, non-destructive evaluation.

Z

Zoom Lens
A compound lens which remains in focus as the image size is varied continuously. May be motorized or manually operated.

Zoom Range
The ratio between the highest magnification and the lowest magnification in a zoom system.