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
Angle The field of view, relative to a standard lens within a 35mm still camera, expressed in degrees, e.g. 30°. Practically, this is the area of a scene that a lens covers or sees; where, the angle of view is determined by the focal length of the lens. A wide-angle lens has a short focal length and covers a wider angle of view-than a normal or telephoto lens with a longer focal length.
Aspect Ratio The ratio of width to height, an aspect ration of 9:16 is used in high-definition television (HDTV).
Auto focus (AF) System by which the camera lens automatically focuses on a selected part of the picture subject.
Automatic iris A lens controlled by a mechanism coupled to the shutter release in the camera body. A diaphragm closes to any preset value before the shutter opens and returns to the fully open position when the shutter closes.
Bitmap A bitmap defines a display space and the colour for each pixel or "bit" in the display space. GIF and a JPEG are examples of graphic image file types that contain bit maps. A bit map does not need to contain a bit of colour-coded information for each pixel on every row. It only needs to contain information indicating a new colour as the display scans along a row. Thus, an image with much solid colour will tend to require a small bit map. Because a bit map uses a fixed ‘raster’ method for specifying an image, a user cannot immediately rescale the image without losing definition. Conversely, a vector graphic image is designed to be quickly rescaled. When an artist is satisfied with an image, it is typically created using vector graphics and then converted to (or saved as) a raster graphic file, or bit map.
CCD – Charge Coupled Device The light-sensitive image device within most modern cameras, this is a large-scale integrated circuit containing hundreds of thousands of photo-sites (pixels) that convert light energy into electronic signals. Its size is measured diagonally and can be 1/4", 1/3", 1/2" or 2/3". CCD stands for Charge Coupled Device, which is the new age imaging device, replacing the old image tube. When first invented in the 1970s, it was initially intended to be used as a memory device. Most often used in cameras, but also in Telephone, fax machines, scanners, etc.
CCTV Closed Circuit Television, also known by the acronym CCTV, is a private video system within a building (or complex) used to visually monitor a location for security or industrial purposes. A CCTV system can be recorded and viewed on-site or viewed remotely through the use of telephone lines.
CIF CIF (Common Intermediate Format) refers to video resolution 352 x 288 pixels (PAL) and 352 x 240 pixels (NTSC).
Coax cable Coax cable is the standard means of transmitting video in a CCTV system. Coax is the same type of cable used by cable companies to send television into the home.
Control unit If a CCTV system has more than one camera, there must be a way to control each video signal going to the VCR and the monitor. There are three basic types of Video Control Units, Multiplexor, Switch and Quad.
DSP Digital Signal Processor. This is a circuit that is specially designed for digital signals in processor-intensive applications, such as wireless communications links and image processing. DSP circuits are often used in consumer products, such as mobile phones, faxes and digital televisions.
DVD Digital Versatile Disc. An optic disc with the same physical size as a CD but with significantly greater storage capacity.
Field In video, this is one vertical sweep of a raster scan. In 1:1, 2:1 and 4:1 interlaced video, one, two, and four fields respectively make up a video frame.
Frame A frame is a complete video picture. In the 2:1 interlaced scanning format of the RS-170 and CCIR formats, a frame is made up of two separate fields of 262.5 or 312.5 lines interlaced at 60 or 50 Hz to form a complete frame which appears at 30 or 25 Hz. In video cameras with a progressive scan, each frame is scanned line-by-line and not interlaced; most are also presented at 30 and 25 Hz.
GIF (Graphics Interchange Format) A GIF (some people say "DJIF" and others say "GIF" with a hard G) is one of the two most common file formats for graphic images on the World Wide Web. The other is the JPEG.
On the Web and elsewhere on the Internet (for example, bulletin board services), GIF has become a de facto standard image format. CompuServe owns the format, and companies commercially developing products exploiting the format need to buy a license. Ordinary Web users and businesses publishing GIF images on their Web sites do not need a license.
Technically, a GIF uses the 2D raster data type, is encoded in binary, and uses LZW compression. There are two versions of the format, 87a and 89a. Version 89a (July, 1989) allows for the possibility of an animated GIF, which is a short sequence of images within a single GIF file. A GIF89a can also be specified for interlaced presentation.
An Internet committee has developed a patent-free replacement for the GIF, the PNG format, and major browsers will soon be supporting it.
Image compression Image compression minimizes the size of a graphics file (in bytes) without seriously degrading the quality of the image. The reduction in file size for a small and acceptable degradation in image quality allows more images to be stored within a limited disk or memory space. It also reduces the time required for images to be sent over the Internet or downloaded from Web pages.
There are several different ways in which image files can be compressed. For Internet use, the two most common compressed graphic image formats are the JPEG format and the GIF format. The JPEG method is more often used for photographs, while the GIF method is commonly used for line art and other images in which geometric shapes are relatively simple.
Other promising techniques for image compression include the use of fractals and wavelets. And, although these methods have not yet gained widespread acceptance for use on the Internet, both formats do offer significantly higher compression ratios than either JPEG, or GIF. Another new image standard that may in time supersede the popular GIF format is PNG (Portable Network Graphics) format.
A text file or program can be compressed without the introduction of errors, but only to a certain point. This is called ‘lossy compression’. And, beyond this point, errors are introduced. In text and program files, it is crucial that the compression process does cause loss of data, because a single error may seriously damage the meaning of a text file, or prevent a program from running. In image compression, a small loss in quality is usually not noticeable. There is no ‘critical point’ up to which compression works perfectly and beyond which point it becomes impossible. But when tolerance for some data loss is acceptable, the compression factor may be greater than it might otherwise be for compression with zero tolerance loss. For this reason, graphic images can be compressed more than text files or programs.
JPEG (Joint Photographic Experts Group) To create a JPEG (pronounced JAY-peg) graphic image a level of compression must be chosen from a suite of compression algorithms. When creating or converting a JPEG image from another format, you are asked to specify the quality of image you want. Since the highest quality results in the largest file, you can make a trade-off between image quality and file size. Officially, the JPEG file format is ISO standard 10918. The JPEG scheme includes 29 distinct coding processes although a JPEG implementer may not use them all. Along with the Graphic Interchange Format (GIF) file, the JPEG is a file type supported by the World Wide Web protocol, usually with the file suffix of ‘.jpg’.
You can create a progressive JPEG that is similar to an interlaced GIF.
Monitor A monitor is very similar to a standard television set, however, it lacks the electronics to pick up regular television. Monitors are available in both monochrome and color versions.
MPEG (Moving Picture Experts Group) MPEG (pronounced EHM-pehg), the Moving Picture Experts Group, develops standards for digital video and digital audio compression. It operates under the auspices of the International Organization for Standardization (ISO). The MPEG standards are an evolving series, each designed for a different purpose.
To use MPEG video files, you need a personal computer with sufficient processor speed, internal memory, and hard disk space to handle and play the typically large MPEG file (which has a file name suffix of .mpg). You also need an MPEG viewer, or client software that plays MPEG files. (Note that .mp3 file suffixes indicate MP3 (MPEG-1 audio layer-3) files, not MPEG-3 standard files.) You can download shareware or commercial MPEG players from a number of sites on the Web.
Multiplexers These units are high-speed switches that provide full-screen images from up to 16 cameras. Multiplexers can playback everything that happened on any one camera without interference from the other cameras on the system.
Quads A Quad displays images from up to four cameras on a single screen; where, the images from each camera take up approximately a quarter of the display area. Optionally, the visual information from each camera can be simultaneously recorded—but only in the small quad format at quarter-screen resolution.
Resolution Resolution is a measure of how clear and crisp an image appears on a monitor. As each piece of CCTV equipment included within a system contributes to the overall image quality, the resultant image can only be as clear as the piece of equipment with the lowest resolution. If you are using a high-resolution monitor together with a low-resolution camera, the monitor can only display low-resolution images. This observation becomes increasingly important when using the system for recording. The playback image quality from a tape is typically a half of that displayed within a normal monitor. So, be sure that the system can deliver the resolution your application demands before installing the system!
System on a chip (SOC) An ASIC that is specially developed to meet the requirements of a given application in which the objective is to integrate most functionality on a single chip, thereby realizing benefits in terms of price, performance and reliability. Examples of functions that are often integrated in an SOC are microprocessors, memory and interfaces.
Sharpness This is the control of fine detail within a picture, independent of content. At least, that’s what it is supposed to mean. The feature was originally introduced into color TV sets that used notch filter decoders—which includes almost every color TV launched onto the market before the mid-1980’s. The filter took away all high frequency detail in the black and white region of the picture. The sharpness control attempted to put some of that detail back in the picture. Although sharpness control was unnecessary on many expensive sets that included comb filters, manufacturers were reluctant to remove a popular control mechanism that consumers had seen on TV sets for years. With sharpness controls pretty much superfluous in high-end TVs, the only logical requirement for sharpness control nowadays is on a VHS machine. Notably, there is no sharpness control included on direct view sets designed for DTV.
Tilt The rotation of a camera along its perpendicular line of sight, i.e. moving a camera target vertically. If animated, a nodding effect is achieved.
Time-lapse recorder The type of video recorder commonly used in the security industry has the ability to record up to one-week of video on a single tape. The most commonly used timing is the 24-hour mode. Having to change tapes only once a day and retaining large amounts of information are perceived as key advantages in using this particular mode of recording.
TVL TV Lines, a method to define resolutions within analogue video.
Video camera The modern CCTV video camera is available in both monochrome (black and white) and color. Cameras can be set in fixed-positions or placed on 'pan-and-tilt' devices that allow the camera to be moved up, down, left and right. Using a zoom lens provides a closer view of the person, or object, you wish to see.
Video Switchers These units sequentially display full screen images, one camera after another typically at 3 to 5 seconds intervals. While the image source from one camera is displayed on screen the other camera sources are not being recorded.
Wavelet A wavelet is a mathematical function useful in signal processing and image compression. The use of wavelets for these purposes is a recent development, although the theory is not new. The principles are similar to those of Fourier analysis, which was first developed in the early part of the 19th century.
In signal processing, wavelets make it possible to recover weak signals from noise. This has proven useful especially in the processing of X-ray and magnetic resonance images in medical applications. Images processed in this way can be "cleaned up" without blurring or muddling the details.
In Internet communications, wavelets have been used to compress images to a greater extent than is generally possible with other methods. In some cases, a wavelet-compressed image can be as much as 25% smaller than a JPEG-compressed image of a similar quality. In practice, this can mean that a photograph compressed with JPEG to 200 KB taking a minute to download, can be compressed with wavelet to 50 KB and take only 15 seconds to download.
Wavelet compression works by analyzing an image and converting it into a set of mathematical expressions that can then be decoded by the receiver. A wavelet-compressed image file is often given a name suffix of "WIF." Either your browser must support these files or will require a plug-in program to read the files.
Wavelet compression is not yet widely used on the Web. GIF remains the most common image compression formats, used mainly for drawings, and JPEG, used mainly for photographs.
Zoom Enlarges the view of an object enabling you to see more detail.
In photographic terms, ‘Telescopic’ and ‘Wide’ are general expressions used to describe the varying extremes of the zoom function; where:
