High Speed Imaging Glossary of Terms
In an effort to assist customers and prospective customers to better understand the technical capabilities of high-speed camera systems, nac Image Technology has defined a number of common terms used in the discussion of standard video systems and high speed video systems. Should you, the visitor, not find definitions for those terms in which you are interested, please feel free to contact us at firstname.lastname@example.org to learn more…
Aperture - The opening which allows light to pass through a camera lens. An adjustable diaphragm is used to control the size of the opening.
Artifact - A side effect in video or audio caused by signal processing. In video, artifact is usually a term describing a defect or flaw in the image.
Aspect Ratio - The aspect ratio is the ratio of the width of an image to its height. A standard NTSC image has a 4:3 aspect ratio. Most enhanced and high definition video systems have a 16:9 aspect ratio.
ATC Circuit - The Automatic Temperature Calibration (ATC) Circuit samples the sensor temperature at different temperature points and adjusts the camera’s images to eliminate Fixed Pattern Noise (FPN). As the name implies, this process is completed automatically and requires no user intervention for the setting of black level and/or white balancing.
Average Picture Level (APL) - The average signal level with respect to blanking during the active picture time. APL is expressed as a percentage of the difference between the blanking and reference white levels.
Bandwidth - The range between the lowest and highest limiting frequencies of an electronic system. In video, the term (measured in megahertz (MHz)) is used to describe the technical boundaries of equipment. NTSC television channels have a bandwidth of 6MHz. The greater the bandwidth, the more information a television system can carry.
Beam - The directed flow of bombarding electrons in a television picture tube.
Beam-Splitter Prism - The optical block in a video camera onto which three CCD sensors (or CMOS sensors) are mounted. The optics split the red, green and blue wavelengths of light for the camera.
BNC Connector - Standard twist-connector for attaching coaxial cable to professional video equipment.
Brightness - A measure of the intensity and clarity of an image.
CCD Sensor (Charge-Coupled Device) - A light-sensitive semiconductor used as an image sensor in video cameras.
CMOS Sensor (Complimentary Metal Oxide Semiconductor) - A light-sensitive semiconductor used as an image sensor in video cameras.
Capstan Servo - The regulating device of the capstan as it passes tape through a video tape recorder.
CRT (Cathode Ray Tube) - Display device, or picture tube, for video information.
CCU (Camera Control Unit) - The remote control device used to set parameters for one or more television cameras.
Chrominance - The color information in a television picture. Chrominance can be further broken down into two properties of color: hue and saturation. Also called chroma.
Chrominance-to-Burst Phase - The difference between the expected phase and the actual phase of chrominance portion of the video signal relative to burst phase.
Chrominance-to-Luminance Delay - The difference in time that it takes for the chrominance portion of the video signal to pass through a system relative to the time it takes for the luminance portion. Also called relative chroma time.
Chrominance-to-Luminance Gain - The difference between the gain of the chrominance portion of the video signal and the gain of the luminance portion as they pass through a system.
Clipping - A video circuit that blocks highlights in the video signal which exceed 100 IRE units.
Color Balance - Adjustment of the color circuitry of a television camera to the color temperature of the light source for a given scene.
Color Bars - An electronically-generated test signal usually consisting of six vertical strips of color.
Color Burst - The burst of color subcarrier added to the back porch of the composite video signal. It serves as a frequency and phase reference for the chrominance signal.
Color Temperature - A measurement of the proportional amounts of the three primary colors (red, green, blue) in a light source.
Composite Video - A single video signal containing all of the necessary information to reproduce a color picture.
Contrast - The range in brightness between the darkest and brightest areas of a picture.
Coaxial Cable - A single conductor, braid-shielded cable used to carry video signals. Has a 75 ohm impedance.
Decibel - A logarithmic unit that expresses the ratio between a signal and a reference signal. For voltages, dB = 20 log (Vmeasurement/Vnominal).
Depth of Field - The portion of an image which is in focus.
Differential Gain - Variation in the gain of the chrominance signal as the luminance signal on which it rides is varied from blanking to white level.
Differential Phase - Variation in the phase of the chrominance subcarrier as the luminance signal on which it rides is varied from blanking to white level.
Enhance - A signal processing technique used to sharpen or improve the image.
Exposure Time - Refers to the amount of time available to the sensor for collecting light to form an image. For digital video camera systems, the time is normally stated in milliseconds and/or microseconds. This value can also be stated in fractions of a second, e.g. 1/1000 seconds.
Field - Half of the information in a frame of interlaced video. Represents one complete vertical scan of an image. The NTSC system rate is 59.94 fields per second.
Frame - Two fields of 262.5 interlaced scanning lines. In NTSC, a frame makes up one complete video picture. For digital video camera systems, a frame refers to one complete video picture.
Frame Rate - Refers to the rate of speed at which a high speed video system can record independent frames, e.g. 1,000 fps.
Frequency - The rate of occurrence of events in a system. The frequency of electrical signals is measured in Hertz, or cycles per second.
Frequency Response - A system’s gain characteristic versus frequency. Frequency response is often stated as a range of signal frequencies over which gain varies by less than a specified amount.
Gamma - A term that describes the tonal reproduction characteristics of a video signal.
HDTV Production Standard - An existing standard, known as SMPTE 240M, has been established for the production of high definition television programming. The standard has 1125 lines, 2:1 interlace, a 16:9 aspect ratio and is frame and field compatible with NTSC.
Hertz (Hz) - Once cycle per second. The term was derived from the name of the 19th Century German physicist, Heinrich Hertz.
Hi-G - Refers to the ability of a high speed video camera system to withstand severe shocks of 100G’s or more.
Horizontal Resolution - The number of vertical lines that can be observed by a video camera in a horizontal direction on a TV test chart. (For high-speed digital video cameras, horizontal resolution is also used to describe the number of pixels on an image sensor in the horizontal axis.)
IRE - A relative unit of measure (named for the Institute of Radio Engineers) on a waveform monitor. One IRE equals 1/40th of the composite video signal’s peak-to-peak voltage.
Image Enhancer - A device used to sharpen transition lines in a video picture.
Image Information - There are a number of important measures of the quality of a digital image. Those key aspects of the digital image described in the EOI evaluation report are: spatial resolution, signal to noise ratio, sensitivity, uniformity, modulation transfer function and intrascene dynamic range. A very brief description of these items is described in the Glossary of Terms.
Interlaced Scanning - A display technique in which each TV picture, or frame, is produced using two sequential fields. One field contains the off-numbered lines of the frame, and the other the even-numbered lines. The technique eliminates visible flicker which can be annoying at low frame rates.
Intrascene Dynamic Range - The analysis of the images were done using a standard 8-bit, *.bmp image. For this type of image, there are 256 gray scale steps (total pixel depth) for a monochrome image and 766 gray scale steps (total pixel depth) for a color image. The measure of intrascene dynamic range refers to the intrascene performance, i.e. the ability to quantitatively detect the very dim and very bright parts of a single image. In other words, the intrascene dynamic range describes the equivalent number of gray scale steps that can be resolved in the image and this result can be compared to the theoretical number of gray scale steps for the monochrome and color images, respectively.
Kilohertz (KHz) - One thousand cycles per second.
Knee - An intensity range by compressing white levels greater than a preset intensity.
Luminance - The brightness information in the television picture. The luminance signal amplitude varies in proportion to the brightness of the televised scene and is therefore capable of producing a complete monochrome level.
Luminance Nonlinearity - The degree to which the luminance signal gain is affected by changes in luminance level.
Megahertz (MHz) - Millions of cycles per second.
Mega Pixel Resolution - The number of pixels contained by the image sensor is more than 1 Million (e.g. > 1024 X 1024 pixel resolution).
Modulation Transfer Function (MTF) - The MTF describes how much a piece of optical equipment blurs the image of an object. The standard test is to see how well alternating white and black stripes show up (that is, their contrast, the difference between the whitest white and the blackest black) in the image, depending on how finely spaced they are. The MTF is a measure of how much bright-to-dark contrast is lost, as a function of the width of the stripes, as the light goes through the system. So it might be 0.95 for broad stripes, which are not significantly blurred, and 0.10 for ones almost too narrow to be viewed by the system. When reviewing the plots of the MTF, it should be noted that the human eye can resolve .05 to .10 (i.e. 5% to 10% Modulation).
Multi-Camera Head - Refers to a high speed video system where multiple camera heads can be connected to a single Digital Recording Processor (DRP).
NTSC (National Television Systems Committee) - A US engineering group that developed a black & white television standard in the early 1940’s and a color standard in the early 1950’s. Those standards, now called NTSC, are currently used in the United States, Canada and Japan.
PAL (Phase Alternating Line) - The European color television system using a 50 cycle power source, 625 scan lines per frame and 25 frames per second.
Pixel - A picture element, the smallest part of a television imaging device. The basic picture element for CCD and CMOS image sensors, each imaging sensor may have a different pixel design.
RGB - The red, green and blue components of the video signal.
Saturation - The variable property of color that is determined by its purity, or its lack of dilution by white light. Highly saturated colors are vivid, while less saturated colors appear paste.
SECAM (Sequential Color and Memory) - A color television system using a 50 cycle power source, 625 scan lines per frame and 25 frames per second. Color signals are encoded differently from PAL systems. Used in France and parts of the Commonwealth of Independent States.
Self Contained - Refers to a high speed camera system that can be set up in the field and can be operated without a connected PC.
Sensitivity - The measure of sensitivity assists users in obtaining proper exposures and in determining the low light capability of electronic cameras. The International Organization for Standardization (ISO) has published a standard for determining sensitivity which assigns electronic cameras with ISO speed ratings, with these ISO speed ratings being intended to harmonize with film ISO speed ratings. Sensitivity is defined by the ISO committee in terms of ISO film speed equivalent at both excellent (SNR=40) and acceptable (SNR=10) image qualities.
Shutter Speed - Refers to the rotation speed of a mechanical shutter which, due to the width of the shutter opening, has a direct correlation to the amount of time light is available to a sensor to allow the sensor to form an image. For digital video camera systems with an electronic shutter, this term is often used interchangeably with exposure time. For instance, if a digital high speed video camera system operates at 500 fps with a the shutter set to OPEN, the exposure time is 1/500 seconds.
Signal to Noise Ratio (SNR) - SNR is an engineering term for the power ratio between a signal (meaningful information) and background noise. The higher the ratio, the better the image.
SMPTE (Society of Motion Picture and Television Engineers) - An industry organization which sets technical standards and specifications in the film and television industries.
Spatial Resolution - Spatial resolution refers to the camera’s ability to sharply and clearly define the extent or shape of features within an image. It describes how close two features can be within an image and still be resolved as unique. Spatial resolution is stated in cycles/mm or line pairs/mm, two terms that can be used interchangeably.
Ultra High Frame Rate - Refers to a high speed video camera’s ability to record images at 10,000 fps or higher.
Ultra High Light Sensitivity - Refers to a high speed video camera system which is able to capture images with a minimum amount of added illumination, e.g. the Memrecam fx K4’s ability to capture excellent quality images (SNR 40) with a light sensitivity of ISO 8000 at 1000fps with an lens aperture of F4.
Ultra Long Recording Time - Typically refers to high speed camera systems that are capable of recording images at the required frame rate for 45 seconds or more.
Uniformity - By looking at and comparing the value of pixels in a sample “bright” area of an image, the average value of all the pixels is calculated showing the variance of each pixel from the mean. This gives a measure of the evenness of the pixels and, by extension, the consistency of the image. The smaller the standard deviation from the mean, the better the measure of uniformity.
VCR - Videocassette recorder.
Waveform Monitor - A form of oscilloscope which graphically displays the levels of a video signal.
White Balance - The color balancing procedure for a video camera. Allows the camera to “see” white under a given lighting condition.
Zoom Lens - A lens which has a continuously variable focal length from wide angle to telephoto.