Glossary

A

Acid etching - Technique that uniformly thins CCDs to approximately 10 µm so that an image can be focused on the backside of the parallel register where there is no gate structure.

A/D - Acronym for Analog-to-Digital converter; electronic device that converts data from an analog domain to a digital representation.

Adapter - In a camera, the device that allows the camera to be attached to a variety of scientific instruments or lenses. Also called mount adapter, lens mount adapter. See also C-mount, F-mount.

AGC - Automatic gain control.

AIA - Automated Imaging Association.

Aliasing - A pattern of image sampling error in digital systems. Aliasing forces spatial frequency components higher than a critical value (the Nyquist frequency) to be displayed at progressively lower frequencies. Aliasing introduces an undesirable moiré pattern when the spatial frequency of the signal exceeds the sampling rate in a digitizer.

Analog- An information representation scheme with continuous amplitudes. Contrasts with digital, where information is quantized into discrete steps.

Aperture - In an optical instrument, the opening of a lens or aperture stop.

Arc lamps - An electric lamp that produces light by an arc made when a current passes between two incandescent electrodes surrounded by gas. Also called arc light.

Array processor - A specialized digital signal-processing unit capable of handling large-scale arrays (matrices) of computation (such as those encountered in fast Fourier transforms, matrix inversions, and so forth) used in some image-processing tasks.

ASCII (American Standard Code for Information Interchange) - An 8-bit code (7 bits plus 1 parity bit) commonly used to designate alphanumeric and other characters and symbols for computers.

Aspect Ratio - The ratio of width to height for the frame of the televised picture. 4:3 for standard systems, 5:4 for 1K x 1K, and 16:9 for HDTV.

Asynchronous - Digital operations triggered by external, untimed events and not by a fixed frequency clock. Signals which clock independently from each other.

Automatic Gain Control (AGC) - A circuit by which electronic gain is automatically adjusted as a function of input intensity or other specified parameter, in order to retain the output at constant level.

B

Backside-illuminated CCDs - CCDs that have been uniformly reduced to a thickness of approximately 10 µm so that an image can be focused on the backside of its parallel register (where there is no gate structure). Thinned CCDs exhibit a high sensitivity to photons ranging from the soft x-ray to the near-infrared regions of the spectrum.

Back Porch - That portion of the composite picture signal which lies between the trailing edge of the horizontal sync pulse and the trailing edge of the corresponding blanking pulse.

Bandwidth - The difference between the upper and lower limit of a frequency band expressed in number of cycles per second (Hertz).

Baud rate - The number of bits per second at which a digital signal is transmitted from one digital computer to another, for example, over a telephone line.

Beamsplitter - A device for dividing a light beam into two or more separate beams.

Binned readout - Within a sensor, the process of moving charge that has been binned to an output amplifier for conversion to an image. Contrasts with sensor readout and subarray readout. See binning, output amplifier.

Binning - In imaging technology, the technique of combining the charge from adjacent pixels so that the total charge can be read out as an image. See parallel binning, serial binning.

Binning factor - The number of pixels to be combined on the sensor during binning. A binning factor of 2x2 means that pixels in two rows and two columns (a total of four pixels) are combined for readout. See also parallel binning factor, serial binning factor.

Bit - A contraction of binary digit, the smallest unit of information in a notation using the binary system (1 or 0). A byte is commonly made up of 8 bits.

Bit depth - The number of bits that are digitized by the A/D converter.

Blooming - The defocusing of regions of the picture where the brightness is at an excessive level, due to enlargement of spot size and halation of the fluorescent screen of the cathode-ray picture tube. In a camera, sensor element saturation and excess which causes widening of the spatial representation of a spot light source.

BNC connector - A coaxial type of connector used to couple coaxial cables to video and other high-frequency electronic equipment.

Bulb mode - Type of exposure wherein a trigger signal from an external source controls the start and end of the exposure.

Bus - A parallel set of wires in a computer over which control and data are exchanged between the various devices (terminal, CPU, memory, ALU, and so forth) connected to the bus. The bus can be standardized following IEEE recommended standards or may be a special bus (such as a video bus) that allows rapid interchange of specific information. A system-level bus will generally contain four component buses: the data bus, address bus, control or status bus, and power bus. The bus provides great flexibility to a computer, permitting different (internal and peripheral) devices to be plugged in, actuated, and signals to be exchanged.

C

Candela (cd) - The luminous intensity emitted by a standard source of light. One candela emits one lumen per steradian.

CCD - Charge-coupled device.

CCTV - Closed-circuit television

cd - Abbreviation for candela.

Charge - In CCD camera imagers, a measure of the number of electrons confined by a pixel.

Charge smearing - Residual charge left behind in potential wells when an image is shifted within a CCD.

Charge transfer - (1) In CCD image technology, the ability of the CCD to transfer the charge in each individual pixel onto the next pixel without any loss in the charge during the transfer. Scientific-grade CCDs typically have a CTE of 99.9998%, where 100% is perfect. (2) Process by which the electrons in a given potential well are moved into an adjacent well. Also called charge-transfer efficiency (CTE).

Charge-coupled device (CCD) - A light-sensitive imaging silicon chip used in cameras.

Chip - A very small piece of silicon processed or burned to form an integrated circuit. Short for integrated-circuit chip. See integrated circuit.

Chroma - That quality of color which embraces both hue and saturation. White, black, and grays have no chroma.

Chroma Control - A control of color television receiver that regulates the saturation (vividness) of colors in a color picture.

Chroma Detector - Detects the absence of chrominance information in a color encoder input. The chroma detector automatically deletes the color burst from the color encoder output when the absence of chrominance is detected.

Chromatic Aberration - An optical defect of a lens which causes different colors or wave lengths of light to be focused at different distances from the lens. It is seen as color fringes or halos along edges and around every point in the image.

Chromaticity - The color quality of light which is defined by the wavelength (hue) and saturation. Chromaticity defines all the qualities of color except its brightness.

Chrominance - A color term defining the hue and saturation of a color. Does not refer to brightness.

Chrominance Signal - That portion of the NTSC or PAL color television signal which contains the color information.

C-mount - Standard screw-in lens mount found on many scientific instruments, including most CCTV video cameras. The thread of the lens and lens mount is 1 inch in diameter with 32 threads/inch and with a back focal length of 17.52 mm.

CMOS (Complementary Metal Oxide Semiconductor) - CMOS sensors are typically used in motion analysis cameras for acquiring high frame rate images. CMOS technology offers high-volume, low cost process of chip manufacturing. Photon collection, timing, control and signal processing are combined on the chip.

Coaxial cable - An electrical cable with a central conductor surrounded by a low-loss insulating sleeve and insulated ground shield. A coaxial cable is capable of passing very high-frequency electronic signals with low signal loss and noise pickup.

Color Burst - That portion of the composite color signal, comprising a few cycles of a sine wave of chrominance subcarrier frequency, which is used to establish a reference for demodulating the chrominance signal. In NTSC, normally approximately 9 cycles of 3.579545 MHz.

Color Edging - Extraneous colors appearing at the edges of colored objects, and differing from the true colors in the object.

Color Encoder - A device which produces an NTSC or PAL color signal from separate R, G, and B video inputs.

Color Fringing - Spurious colors introduced into the picture by the change in position of the televised object from field to field.

Color Purity - The degree to which a color is free of white or any other color. In reference to the operation of a tri-color picture tube it refers to the production of pure red, green or blue illumination of the phosphor dot face plate.

Color Saturation - The degree to which a color is free of white light.

Color Sync Signal - A signal used to establish and to maintain the same color relationships that are transmitted.

Color Transmission - The transmission of a signal which represents both the brightness values and the color values in a picture.

Compatibility - The ability of one piece of equipment to interface and function with another.

Composite Video Signal - The combined picture signal, including vertical and horizontal blanking and synchronizing signals.

Contrast - A measure of the gradation in luminance that provides gray-scale (or color) information. Contrast is expressed as the ratio (difference in luminance)/(average luminance) in adjoining areas of the scene. Under optimum conditions, the human eye can just detect the presence of 2% contrast.

Contrast enhancement/stretching - In digital image processing, the enhancement of contrast by using an image histogram and lookup table. Can also be achieved with analog devices.

Contrast range - The range of gray between the lightest and darkest parts of an image; expressed as a ratio of light to dark. See also dynamic range.

Cooled CCD - A CCD image pickup device that operates at temperatures below ambient to reduce or eliminate dark current. Cooling is usually done with Peltier coolers or cooled liquid gases.

Counts - See digital number.

D

D/A converter - A circuit used at the output of a digital computer or processor to provide analog signals of power. A DAC is sometimes used to drive a standard video monitor.

Dark current - (1) In the absence of light, charge accumulated in a well. (2) The background current that flows in a photodetector such as an image intensifier, VIDICON, or CCD. Usually it can be eliminated, when required, by cooling the photodetector's primary image pickup surface such as the photoconductor or photocathode. Also called thermally generated charge.

Dark noise - Dark current and any other noise accumulated in the absence of light. Also called dark current noise.

Definition - The degree of detail or sharpness in a displayed image.

Depth of field - The distance between the closest and farthest objects in focus within a scene as viewed by a lens at a particular focus and with given settings. The depth of field varies with the focal length of the lens and its f-stop setting or NA (numerical aperture) and the wavelength of light.

Depth of focus - The range of distances between a lens and image plane (target in the pickup device) for which the image formed by the lens at a given setting is clearly focused.

Digital number (DN) - A number representing the CCD output. Also called counts.

Digital signal - A signal whose units are represented by either one of only two states: on or off, yes or no, 1 or 0. Since no gradations in between are permitted, digital signals are precise, unambiguous, and quite immune to noise. See also analog.

Digital-to-analog converter - See D/A converter.

Digitize - To convert (as data or an image) to digital form.

Digital Number (DN) - The gray level output from a digital camera (0-255 for an 8-bit system or 0-4095 for a 12-bit system).

Dynamic range - The ratio of the maximum to minimum signal levels that introduce no more than acceptable levels of signal amplitude distortions.

E

Electronic camera - A camera that produces an electronically scanned image or series of images. Both tube and CCD cameras are electronic cameras, as opposed to a camera whose output is film.

Exposure - The total radiant energy incident on a surface per unit area. It is the product of integration time and the radiant flux density.

Exposure time - Length of time the sensor is accumulating charge. In CMOS cameras, the time between sensor reset and sensor read out. In CCD camera technology, the length of time for a full parallel shift sequence to occur.

F

Faceplate - The window that the input or output radiation passes through on a camera tube, monitor picture tube, and solid-state array. Sometimes used to support a target or phosphor.

Fiberoptics - Thin transparent fibers of glass or plastic that are enclosed by material of a lower index of refraction and that transmit light throughout their length by internal reflections. Also, a bundle of such fibers used in an instrument.

Field of View - The total area of object space imaged at the focal plane of a camera.

Fill factor - As relates to the light gathering area of a sensor such as CMOS or CCD . For example, 40% of a pixel's area may be used for charge and or current handling and processing, making this area insensitive to light. Therefore, in this example, the sensor would only have a 60% fill factor.

Fixed Pattern Noise (FPN) - Pixel to pixel output nonuniformity measured under dark conditions.

Flat Field Correction - Flat Field correction involves subtracting the image information from an empty field of view from that of the same field of view with the sample added. This process subtracts all background image information associated with such things as uneven lighting sources, lens dust etc.

F-mount - Standard lens mount found on many scientific instruments. The thread of the lens and lens mount is 2.5 mm in diameter with a back focal length of 46.5 mm.

Focal Length - The distance from a lens principal point to the corresponding focal point. Also referred to as the equivalent focal length and the effective focal length; e.g. a 50mm lens.

Focal Plane - A plane orthogonal to the optical axis of a lens at which the sensor array resides.

Focus - The point or plane in which light rays form a minimum-sized spot that has the proper intensity distribution. Also the act of bringing light to a fine spot.

Footcandle (ft) - A measurement of illuminance, or illumination expressed in lumens per square foot. It is the amount of illumination from 1 international candle (the candela) falling on a 1-ft. surface at a distance of 1 foot. In SI units, 1 fc = 10.764 lux (1x). See Burle Electro-Optics Handbook.

FPS - Frames per second.

Frame - A two-dimensional array of pixels or pixel information or a complete read-out of all pixels from a camera.

Frame buffer - In a digital image processor, the hardware in which the frame memory resides. The frame memory is a RAM that stores a full frame of the video image signal.

Framegrabber - Adevice which interfaces between a camera and computer.

Frame Rate or Read Out Rate - The speed at which images are captured by an imaging system is called the frame rate and is expressed as number of frames per second FPS. Higher frame rates are far better for easier focusing and sample positioning and general ease of use. Live action on a television is typically 28FPS, which prevents stuttering on the image.

Frame transfer - See frame-transfer CCD imager.

Frame-transfer CCD imager - A type of CCD imager used for quantitive electronic imaging. The frame-transfer CCD imager divides the parallel register into two areas (arrays): image array (for image collection) and storage array (for image storage). After the image array is exposed to light, the electronic image is shifted to the storage array and readout. A frame-transfer CCD imager can operate without a shutter, running continuously and at a high rate. Contrasts with full-frame-transfer CCD imager and interline-transfer CCD imager.

Frequency - The number of times per second a repetitive signal undergoes a full cycle of vibration. Frequency units are Hertz (Hz). For spatial frequency, the number of cycles of image brightness variation along a scan direction, generally expressed in lines per millimeter or line pairs per millimeter.

Front Porch - The portion of a composite picture signal which lies between the leading edge of the horizontal blanking pulse and the leading edge of the corresponding sync pulse.

f/Stop - Also called F Number and F System. Refers to the speed or ability of a lens to pass light. It is calculated by dividing the focal length of the lens by its diameter.

f/Stop Ratio - This number is the ratio that describes the focal distance, as determined by the diameter of the lens aperture. So the greater the aperture the lower the f-stop value; the more light strikes the sensor, the greater the sensitivity. Zoom capability is sacrificed with very low f-stops.

Full-frame - See full-frame CCD imager.

Full-frame CCD imager - The simplest type of CCD imager. The full-frame imager uses the entire parallel register to expose photons and to integrate and transport charge. It uses a shutter to control the exposure and to block light during readout, preventing charge smearing. Contrasts with frame-transfer CCD imager and interline-transfer CCD imager.

Full-well capacity - Number of electrons that can be held in one potential well.

G

Gain - In digital cameras, system gain defines the relationship between the number of electrons acquired on the sensor and the analog-digital units (ADUs) generated.

Gain (image intensifier) - Can be expressed in many ways such as the ratio of output energy to input energy, or output power to input power. For image intensifiers it could be expressed as luminous gain, radiant emmitance gain or photon gain.

Gamma - A numerical value, or the degree of contrast in a television picture, which is the exponent of that power law which is used to approximate the curve of output magnitude versus input magnitude over the region of interest.

Gamma Correction - To provide for a linear transfer characteristic from input to output device.

Gate structure - This polysilicon structure located on the parallel register of a CCD. A gate is transparent at long wavelengths, but becomes opaque at wavelengths shorter than 400 nm.

Gray level - The brightness of pixels as related to a digitized image; commonly expressed in integers ranging from 0 (black) to 255 (white) for an 8-bit digital signal.

Gray scale - The various shades of gray or luminance values in a displayed image. An analog scale that goes from 0 (black) to 10 (white). There are two versions: one is linear, the other is logarithmic.

Gray value - See gray level.

H

High-current switching devices - Any electrical or electronic circuit that turns the current on or off to devices that consume large amounts of current.

High-speed framing - Process by which frames are read from the CCD at a rapid rate.

Host computer - The primary or controlling computer for a digital camera.

Hue - Corresponds to colors such as red, blue, etc.

Hz (Hertz) - Cycles per second. MHz (megahertz) is a million cycles per second.

I

IC - Integrated circuit.

Illuminance - The density of luminous flux incident on a uniformly illuminated area, measured in footcandles (lumens per square foot) or lux (lumens per square meter).

Iillumination - See illuminance.

Image - An optical counterpart of an object formed by lenses or mirrors.

Image analysis - The use of digital computers to derive numerical information regarding selected image features, such as contour lengths, areas, shape, size distribution, and so forth.

Image array - The half of a frame-transfer CCD imager that is exposed to light and in which an image is collected. After the CCD imager is exposed, it is shifted to and stored in the other half of the CCD, the storage array.

Image averaging - A way of reducing snow and other random image noise by averaging the pixel brightness in several successive video frames. Achieved with a digital image processor or by photographic integration.

Image convolution - In manipulating an image with a digital image processor, the substitution of the gray value of each pixel with another gray value that takes into account the gray values of the neighboring pixels. The convolution mask, or kernel, used to calculate the influence of the neighbors, determines the degree to which the image is sharpened or smoothed by the convolution process. Contrasts with point operation, where the gray value of each pixel is transformed without considering the neighbors. Also called convolution.

Image enhancement - A procedure for manipulating the signal to sharpen or otherwise improve the image.

Image intensifiers - A light-in, light-out vacuum-tube device capable of amplifying low-light images. The tube consists of a photocathode on the input and a phosphor on the output, and sometimes a microchannel plate for increased gain characteristics. They are made in two different types: inverter and proximity focused. The inverter type electrostatically focuses and inverts the image inside the tube. The proximity focused type has all of the elements closely spaced, has no need for focus electrodes, and is much more compact.

Image processing - Generally refers to digital or analog enhancement and geometric manipulation of the video signal. Contrasts with image analysis, which emphasizes the measurement of image parameters. See also image analysis, image enhancement.

Image segmentation - In digital image processing, the partitioning of the image into nonoverlapping regions according to gray level, texture, and so forth.

Indium tin oxide - See ITO.

Infrared - Lying outside the visible spectrum at its red end.

Input/out (I/O) bus - See bus.

Integrated circuit (IC) - Electronic circuit conducted on a single semiconductor wafer or microchip.

Integration - The act of accumulating signal or charge on a video sensor such as a CCD. Usually done by inhibiting readout via electronic control of the scan.

Integration Time - The integration time is the time interval that the photoelements are allowed to collect charge.

Interface - Hardware and/or software required to connect peripheral to computer system, one computer system to another, or for user's access to system; point at which any two parts of system connect.

Interline mask - In CCD image technology, opaque strips that span an interline-transfer CCD imager and act as storage areas. See also interline-transfer CCD imager.

Interlaced - A format of video display. Video is produced by updating the odd-number lines on the first scan and the even-numbered lines on the second scan.

Interline transfer - See interline-transfer CCD imager.

Interline-transfer CCD imager - A type of CCD imager in which the parallel register is subdivided so that, like a Venetian blind, opaque strips span and mask the columns of pixels. The masks act as storage areas. When the CCD is exposed to light, the image accumulates in the exposed areas (photosites) of the parallel register. In the serial register, the entire image is under the interline mask when it shifts for readout. Contrasts with frame-transfer CCD imager and full-frame CCD imager.

Inverted operation - See multi-pinned-phase (MPP) operation.

Iris - An adjustable aperture built into a camera lens to permit control of the amount of light passing through the lens.

ITO - Indium tin oxide. A material used in CCD gates to provide higher quantum efficiency.

L

Lens - Transparent pieces of optical glass with curved surfaces that transmit light and cause it to converge or diverge into real or virtual images.

Lumen - A unit of luminous flux, equal to the flux through a unit solid angle (steradian) from a uniform point source of 1 cd. or 1 FC (foot candle) per sq. foot. (See Burle Electro-Optics Handbook, Section 2.1)

Lumigen - A fluorescent coating applied to a CCD to enhance the UV response. Similar to Metachrome.

Luminance - Photometric brightness, or the brightness of light calibrated for a sensor whose spectral response is similar to the light-adapted human eye; measured in nits or footlamberts. See also photometric units.

Lux - The amount of visual light measured in metric units at the surface that the light is luminating. One lux equals one lumen per square meter. One footcandle equals 10.764 lux. (See Burle Electro-Optics Handbook, Section 2.1).

M

Magnification - Relationship of the length of a line in the object plane to the length of the same line in the image plane. It may be expressed as image magnification (image size/object size) or it's inverse, object magnification.

Mask - See interline mask.

Metachrome® II - A coating on a CCD that extends the CCD's sensitivity to below 200 nm. Metachrome II is transparent from 400 to 1100 nm. The coating does not degrade over time.

Moiré - Irregular, wavy pattern.

Monitor - A device that converts the video signal from a camera, VTR, computer, etc. into an image that is displayed on its cathode-ray tube. Compared to a TV receiver that must first decode an RF-modulated video signal, the monitor has no tuner and accepts the signal from the source without demodulation, thus permitting the use of a higher bandwidth and providing greater resolution.

Monochrome - Black and white with all shades of gray.

MPP - Multi-pinned-phase (MPP) operation. Procedure that reduces the rate of dark-current generation by a factor of 20 or more, and thus relaxes CCD cooling requirements to the level where a thermoelectric cooler is sufficient for most applications. Also called inverted operation.

Multi-Camera Synchronization - A feature allowing multiple cameras to have time synchronized data for the purpose of interfacing to a single framegrabber. Allows simultaneous data acquisition from multiple cameras into one framegrabber.

N

Noise - (1) An unwanted signal or a disturbance (as static or variation of voltage) in an electronic device or instrument; electromagnetic radiation (as light or radio waves) that is composed of several frequencies and that involves random changes in frequency or amplitude. (2) A disturbance, especially a random and persistent disturbance, that obscures or reduces the quality or clarity of a signal.

NTSC - Abbreviation for National Television Systems Committee. A committee that worked with the FCC in formulating standards for the present day United States color television system.

Nyquist Theorem - A theorem that, applied to image processing systems, states that the original image can be reconstructed without distortion if it is sampled at a spatial frequency (2f) at least twice that of the maximum constituent frequency (f).

O

Offset - An electronic process that alters the voltages representing an image, putting them into the optimal range for the A/D converter. Offset can be used to compensate for background noise or amplification due to gain.

Opaque mask - In CCD imaging technology, a light-impenetrable material that is used to shield selected parts of a photosensitive surface. Opaque masks are used in interline- and frame-transfer CCD imagers.

Optical coupling - The act of transferring the image from the optical output of one detector to another using lenses. As in optically coupling an image intensifier to a CCD camera.

Optical noise - Image defects that become especially conspicuous when the image is enhanced. In video microscopy, includes hot spots, mottle, uneven illumination.

Origin - In a CCD, the point located closest to the output node.

Output amplifier - In CCD image technology, mechanism in the CCD that takes the electrons in the output node and amplifies them sufficiently to get the signal to the analog-to-digital converter. The output amplifier is the source of read noise.

Output node - The location on the CCD where charge is collected as a discrete picture element for readout.

P

Parallel binning - In CCD imaging, the accumulation of charge (in a pixel) in the CCD's parallel register before the charge is shifted to the serial register. The amount of charge to be shifted is defined by the user-specified binning factor. See binning factor.

Parallel binning factor - In the parallel register of a CCD, the number of pixels (in the parallel direction) to be shifted to the serial register, read out, and processed into an image. The binning factor is specified by the user in the imaging software prior to exposure of the CCD.

Parallel direction - In a serial, parallel (s, p) coordinate system, the direction that starts from the origin and and runs perpendicular to the serial register.

Parallel offset - In a CCD parallel register, the distance (in pixels) between the serial axis and user-defined, rectangular exposure area on the CCD.

Parallel register - In a CCD, a large, square array that contains many potential wells (pixels). When the CCD is exposed to light, charge accumulates in the potential wells, which, when shifted and read out, form an image.

Parallel shift - In a CCD, columnar movement of charge from one or more pixels to an adjacent row. The movement continues until the number of pixels the user specifies to be binned are emptied into the serial register.

Parallel size - In CCD image technology, the size of the region of interest (in pixels) extending in the parallel direction.

Phosphor - Substance that is capable of luminescence.

Photometric units - The units (1 m, l x, cd/m, etc.) that are used to measure the amount of light (illuminance) or the brightness of an object or image (luminance), taking into account the sensitometric characteristics (wavelength-dependent response) of the human eye. Contrasts with radiometric units (for example, W/m), which measure light in terms of the physical energy independent of the sensitometric characteristics of the eye.

Photon - Massless quantum of electromagnetic radiation or light energy.

Photon (shot) noise - Unwanted or undesirable disturbance that is a fundamental property of the quantum nature of light. Created by photons emitting a steady source of time and photoelectrons collected by a CCD. Photon noise is unavoidable and is always present in an imaging system. It equals the square root of the mean signal.

Photon-limited operation - The use of chilled photomultipliers, charge-coupled devices, or intensifier camera tubes at levels of light and noise so low that individual photons can give rise to clearly detectable bursts of electrons. Commonly, about 10% of the absorbed photons trigger a signal, and the level of energy of the electrons is statistically distributed. Also called photon-counting mode, quantum-limited mode.

Picture - A visual representation or image of something. See also image.

Pixel - Picture element; a single dot and smallest element in a visual display.

Poisson distribution - A probability density function that is often used as a mathematical model of the number of outcomes obtained in a suitable interval of time and space.

POT - Potentiometer.

Potentiometer (POT) - A center-tapped variable resistor, generally used for adjusting the signal or bias voltage levels.

Preamplifier noise - In CCD imaging, unwanted signal or disturbance that is generated by the on-chip output amplifier. The noise can be reduced to a few electrons by modifying operating conditions. Also called read noise. See also output amplifier.

Primary Colors - Three colors wherein no mixture of any two can produce the third. In color television these are the additive primary colors red, blue and green.

Progressive Scan - The progressive scan format outputs data from the camera (the signal) in sequential order as it is scanned. The scan format produces a full frame of video in a continuous stream, rather than half the image per output sequence in traditional RS-170 CCD cameras. Standard RS-170 video is interlaced and output in two separate fields, generating essentially half the image at a time. With Cohu's new 6600 Series Progressive Scan Camera, a new, full image is output from the camera every 1/60th second, making it ideal for machines to more quickly process and display information, or act according to programmed instructions.

Q

Quantum efficiency - The measure of the effectiveness of an imager to produce electronic charge from incident photons. Especially important to perform low-light-level imaging.

R

Read noise - See preamplifier noise.

Readout - In CCD imaging, the removal of charge from the serial register to signal processing. The signal processing translates the charge into an image.

Region - In CCD imaging, a user-defined, rectangular area on the CCD that is exposed and processed as an image.

Region definition - In CCD imaging, the area on a CCD that a user selects to be exposed as an image. The user defines the region by specifying coordinates in the serial, parallel (s, p) coordinate system. See serial, parallel (s, p) coordinate system.

Region of interest (ROI) - User-defined, rectangular exposure area on the CCD.

Resolution - A measure of how fine a detail can be detected, in terms of distance in space or passage of time. Note that the convention used to measure spatial resolution in video is every black and white line counted, giving the term "TV lines."

Responsivity - Similar to sensitivity; a rating of the output current from a camera tube or CCD divided by the incident flux of light, usually expressed in signal current per watt of input radiation at a specific wavelength.

ROI - Region of interest.

S

Saturation - In color, the degree to which a color is diluted with white light or is pure. The vividness of a color, described by such terms as bright, deep, pastel, pale, etc. Saturation is directly related to the amplitude of the chrominance signal.

Scientific-grade CCD - Camera component that offers fewer defects than commercial cameras. Scientific-grade CCDs produce better resolution, have low noise, and enable the user to accurately measure intensity differences between objects.

Sensitivity - Similar to responsivity of a camera tube or CCD but numerically different. It is the signal current per unit of illuminance on the faceplate in lumens. It is expressed in amps/lumen. Unless otherwise specified, the radiation is understood to be that of an unfiltered incandescent source at 2,856 degrees K. See also responsivity.

Serial binning - The accumulation of charge in two or more rows of the serial register before the charge is shifted for readout.

Serial binning factor - In the parallel register of a CCD, the number of pixels (in the serial direction) to be shifted to the serial register, read out, and processed into an image. The binning factor is specified by the user in the imaging software prior to exposure of the CCD.

Serial direction - In a serial, parallel (s, p) coordinate system, the direction originating from the origin and moving away from it in a direction parallel to the serial register.

Serial offset - In a CCD parallel register, the distance (in pixels) between the parallel axis and user-defined, rectangular exposure area on the CCD.

Serial, parallel coordinate system (s, p) - In CCD imaging technology, the point of orientation located on the parallel register in the corner closest to the serial register readout. Coordinates increase as the locations move away from the origin. s represents the serial coordinate; p represents the parallel coordinate.

Serial register - In a CCD imager, a one-dimensional CCD adjacent to the parallel register. When the CCD is exposed to light, the serial register receives charge from the parallel register and shifts it to readout to form an image.

Serial shift - In a CCD, the movement of charge (accumulated from the parallel register) to the output amplifier. The charge moves pixel by pixel. From the amplifier, the charge is processed and read out as an image.

Serial size - In CCD image technology, the size of the region of interest (in pixels) extending in the serial direction.

Shutter - A camera attachment that exposes the film or plate by opening and closing an aperture.

Signal-to-noise ratio (SNR) - In CCD imaging, the measure of the signal quality at a given pixel. It is the ratio of the measured signal to the overall noise at that pixel.

Silicon - A tetravalent nonmetallic element that occurs combined as the most abundant element next to oxygen in the earth's crust. Silicon is used especially in alloys and electronic devices.

Slow scan - A system of video scanning in which the time used to read each line has been increased in comparison to standard video. The bandwidth needed to faithfully transmit or record the signal is reduced in inverse ratio to the scanning time. Slow scan allows the video signal to be transmitted over a telephone line, or line scans to be registered on a chart recorder without loss of spatial resolution.

Slow-scan camera - A camera designed to operate at a significantly lower speed than conventional video cameras.

Slow-scan CCD - A CCD image detector that has special circuits allowing for readout of the information at slower-than-standard video rates to reduce readout noise.

SNR - Signal-to-noise ratio.

Spectroscopy - The production and investigation of spectra; the physics that deals with the theory and interpretation of interactions between matter and radiation (as electromagnetic radiation).

Spike - In electronics, a sharp brief voltage pulse. Powerful RF spikes that can damage video equipment and computers are generated when mercury or xenon arc lamps are started. To a limited extent, spikes entering through the power line (but not those rated as RF) can be suppressed with spike arrestors (transient suppressors).

Storage array - In a frame-transfer CCD imager, the half of the parallel register that is covered with an opaque mask to provide temporary storage for collected charge.

STROBE - A camera clocking signal; used for data acquisition. Sometimes referred to as the pixel clock.

Sync - A contraction of "synchronous" or "synchronize".

Sync Generator - A device for generating a synchronizing signal.

Sync Level - The level of the peaks of the synchronizing signal.

Sync Signal - The signal employed for the synchronizing of scanning.

Synchronizing - Maintaining two or more scanning processes in phase.

System noise - In CCD imaging, undesirable signals or disturbance generated by electronic circuitry. System noise includes photon noise, preamplifier noise, and dark current noise.

T

TDI - Time-delay integration.

Thermally generated charge - See dark current.

Thermoelectric cooling - In CCD imaging, the process of pulling heat away from a CCD by using Peltier cooling devices.

Thinning - Process that uses acid etching to uniformly reduce the size of CCDs to approximately 10 µm so that an image can be focused on the backside of its parallel register (where there is no gate structure). Thinned CCDs exhibit a high sensitivity to photons ranging from the soft x-ray to the near-infrared regions of the spectrum.

Time-delay integration - An integration and readout mode that allows the acquisition of long swaths of a moving image.

Trigger - Signal (typically a TTL signal) that is transmitted to synchronize two or more instruments; something that acts like a mechanical initiator in setting up a process or reaction.

U

Ultraviolet - Of or pertaining to the range of radiation wavelengths from about 4000 angstroms (just beyond the violet in the visible spectrum) to about 40 angstroms (on the border of the x-ray region).

Unichrome - A coating on a CCD that extends the CCD's sensitivity to below 200 nm. Unichrome is transparent from 400 to 1100 nm. The coating does not degrade over time.

V

Video camera - Camera for electronically processed videotape that requires no developing.

Vignetting - An image with a reduction in brightness in the periphery is usually caused by the use of a lens that produces an image circle smaller than the sensor size. For instance, if you place a 2/3" lens that produces an image circle of 11 mm onto a camera that has a sensor 22 mm in diameter the vignetting will be very noticeable.

Voltage - Electric potential or potential difference expressed in volts.

W

Wavelength - In a periodic wave, the distance between two points of corresponding phase in consecutive cycles.

Well Capacity - The total number of electrons a pixel can hold before blooming. Also called the Saturation level.

X

X-ray - High-energy photon with a wavelength in the approximate range from 0.05 angstroms to 100 angstroms.