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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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