1999 Conference Proceedings

Go to previous article 
Go to next article 
Return to 1999 Conference Table of Contents


CONTEMPORARY CLOSED CIRCUIT TELEVISION SYSTEMS

Alec F. Peck
Special Education
Boston College
email: peck@bc.edu 

Mark M. Uslan, Manager
Technical Evaluation Services
American Foundation for the Blind
email: muslan@afb.net

The popularity of CCTV systems for visually impaired people has grown dramatically since it was first introduced in the early 1970s. Among the design-factors that effect CCTV usage are convenience, image quality, magnification range, range of focus, and cost. This presentation will describe the features of today's most popular CCTV's and discuss the products which are used by a sample of people who own them. Selected data from an analysis of 150 CCTV users in AFB's Careers and Technology Information Bank will be presented.

Today's CCTVs are of three types -- systems in which the camera or display or both are mounted on a stand, those that use a handheld camera, and those that head-mount the camera and/or display. Since head-mounted systems are not in wide-spread use, they will not be addressed in detail in this presentation.

Most stand-mounted systems provide in-line viewing, that is, the display is mounted directly above and in line with the material to be viewed. They consist of a display that either rests on top of a platform that houses the camera and controls or is affixed to it and an x-y table that is attached to the base. When the display sits on the platform, it is possible to remove the display and place it alongside the camera at a distance limited by the length of the cable. When only the camera is mounted on the stand, the camera and display must be placed side by side.

Stand-mounted CCTV systems are commonly configured with either television receivers, video monitors, or computer monitors. They provide high-contrast, gray-scale, and inverse video-display modes with adjustments for levels of contrast and brightness. Although most use black-and-white cameras, color systems with color cameras and monitors are available. Resolution is somewhat diminished in a color system due to color picture tube electronics. Also, a high contrast mode is not used in a color system because it would wash out the colors that are close to each other on the color spectrum. Some color systems can toggle between a color mode and a black and white grey scale mode.

Most video monitors use a method of projecting the image on the screen known as non-interlace scanning, which provides better resolution. Newer TV receivers also have direct video-input jacks that enable them to function as video monitors and hence to provide higher quality images.

A CCTV system that uses a computer monitor can receive display output from the computer and combine the computer image and CCTV image on a split-screen display. A color monitor can also offer foreground-background color options so black-and-white tones can be remapped to other colors.

Stand-mounted CCTV systems provide enough space between the camera and the x-y table to allow for handwriting. They are heavy, weighing between 26 and 45 pounds, with 50-75 percent of the weight attributed to the cathode ray tube (CRT) monitor. Large monitors and TVs are placed alongside the camera stand or are supported by a separate monitor stand. Black-and-white stand-mounted systems typically cost between $1,800 and $2,600, and color systems cost an additional $400 to $1,000.

Since a major design consideration is the support of the large and heavy CRT monitor, stand-mounted structures are fabricated for stability and durability, not portability. At their lowest magnification levels, stand-mounted systems have a focusing range of no more than a few inches which means that if you are focused on a sheet of paper and then put a thick book under the camera, you will need to refocus. To overcome this problem, some CCTV manufacturers have applied infrared autofocus technology to maintain a clearly focused image throughout the camera's magnification range.

Handheld systems typically consist of a camera and a control box with a cable to be connected to a TV, video monitor, or computer monitor. Since there is no mounting stand, the camera and the display must be placed adjacent to each other. The user holds the camera and moves it across and down a page. Handwriting under the camera is possible by mounting the camera either on a stationary stand or a small, lightweight stand that is moved over the material to be viewed. To enhance the portability of handheld systems, users can connect them to either a 5-7 inch TV or video monitor or a head-mounted display (HMD).

Most handheld systems provide high-contrast, gray-scale, and inverse video-display modes, and some offer color cameras. For those handheld cameras that have a fixed magnification level, the amount of magnification attainable is dependent solely on the size of the display. Their cameras are placed on the material to be viewed; at any distance above the material they lose focus. In hand-held systems that have a large focusing range it is possible to vary magnification by changing the height of the camera above the viewing material.

Handheld cameras do not require the structural support that stand-mounted systems do, and since they are moved over the material to be viewed, an x-y table is not needed. Consequently, they are lightweight (5-16 ounces); however, their portability is limited by the necessity to connect their cameras to displays. Many of today's portable handheld systems are configured with a rechargeable battery, a small, lightweight display, and an over-the-shoulder carrying case that enables the user to operate the system without having to place it on a table. For between $400 and $1,200, it is possible to purchase a basic handheld system consisting of a handheld camera and a TV control box. However, the price can more than double for a portable handheld system, primarily because of the cost of the rechargeable battery pack and the portable display.

The flat-panel display, which is commonly found in laptop computers, can also be used in the design of portable CCTV systems. One such system uses a handheld camera and provides the option of using a TV or a 6 inch TFT active matrix liquid crystal display whose brightness and contrast are comparable to the 5 inch TV display. Although the 6 inch TFT display panel is more expensive than a 5 inch TV, it is only a few inches thick and thus is easily portable. The cost of TFT display technology for larger displays is prohibitive.

CCTV is used by a substantial number of persons with visual impairment. This presentation includes discussion of the characteristics which users report to be of particular benefit to them.

REFERENCES

Uslan, M.M. (1994a). A review of HumanWare's 'ViewPoint' series of closed-circuit television systems. Journal of Visual Impairment and Blindness (JVIB), News Service. vol 88, no. 3. pp 13-17.

Uslan, M.M. (1994b). A review of two low-cost closed-circuit television systems. Journal of Visual Impairment and Blindness (JVIB), News Service. vol 88, no. 6. pp 13-16.

Uslan, M.M. (1994c). A review of Acrontech's "Executive" series of closed circuit television systems. Journal of Visual Impairment and Blindness (JVIB), News Service. vol 88, no. 1. pp 14-20.

Uslan, M.M., and Shen, R. (1995a). A review of three low cost stand-mounted closed-circuit television systems. Journal of Visual Impairment and Blindness (JVIB), News Service. In press.

Uslan, M.M., and Shen, R. (1995b). A review of Acrontech's Elite series closed-circuit television systems. Journal of Visual Impairment and Blindness (JVIB), News Service. In press.

Uslan, M.M., and Shen, R. (1995c). A review of three CCTV systems that offer varying degrees of portability. Journal of Visual Impairment and Blindness (JVIB), News Service. In press.

Uslan, M.M., Shen, R., and Shragai, Y. (1996). The evolution of video magnification technology. Journal of Visual Impairment and Blindness, 90(6), 465-478.


Go to previous article 
Go to next article 
Return to 1999 Conference Table of Contents 
Return to Table of Proceedings


Reprinted with author(s) permission. Author(s) retain copyright.