Some information about Video Images
Pro's and Con's
Pro's
A video surveillance system can capture a continues sequence of events normally fast enough to not miss anything that is happening in front of the camera.
A time-lapse video system can continuously monitor and record an area for Hours, Day's, and in some cases almost a week on a single unattended tape.
With special multiplexing equipment 2,4,6, and sometimes 8 cameras can be put on the same tape at the same time allowing multiple areas to be watched and recorded. Or the system can automatically or manually be switch between cameras allowing a full field of each camera, or a combination of both techniques can be used.
Con's
A video image is made up of a number horizontal lines that as they move down the screen or across the video tape make up the image area of a video frame. Each point on each of these single lines is lightened or darkened to respond to the brightness of the original image at that point in the subject. These lines are referred to as the " Lines of Resolution " A normal television signal contains 525 lines of resolution with only about 480 of these making up the image that you see on the normal Television screen. Most video recorders only record and playback approx. 250 lines of resolution. VHS is around 250 280 lines, SVHS, and Hi-8 will record at 480 lines of resolution.
A normal Television picture has 30 new images each second to give what the human eye perceives as a continues motion of an object on the screen. In time-laps video systems this process is changed somewhat and can give a complete frame once or twice each second or maybe one frame every 5 seconds or more. This slowing down gives the taped images a jerky sped up look when viewed on a normal VCR, and in some cases a normal VCR may not reproduce viewable image from the tape at all . In the slower modes of operation the time spans between images can mean that a subject can move far enough between frames to never get a good detailed captured image.
When Multiplexing is used to allow more than one image to be recorded on the same tape at the same time, each resulting image from each camera is given less room to record the video information on the tape. This process results in a video camera with 250 lines of resolution being recorded with only maybe 125 lines on the tape. The resulting images are very highly lacking in any recorded image detail. Even a suspect in fairly close view of the camera will be of poor image quality and if the subject is some distance from the camera and their entire face may only comprise 2 or 3 lines of the image, not enough to be able to make any kind of positive identification from. If a switching system is used the recorder may be taping a different camera during the time that a person or object of interest is in view of a camera that is for all practical purposes turned off.
This page is still under construction, please check back again.