Useful Information
- ♦ Application
- ♦ Cameras
- ♦ Lenses
- ♦ Light & CCTV
- ♦ Number Plate Recognition
- ♦ Thermal Imaging
- ♦ Housings
- ♦ Digital Images
- ♦ Digital Technology & Recording
- ♦ Video Compression
- ♦ Infrared
- ♦ IR & LED Lighting
- ♦ IP CCTV & Technology
- ♦ Monitors
- ♦ Motion Detection
- ♦ Multiplexers
- ♦ PIR Movement Sensor
- ♦ Remote Positioning Devices
- ♦ Video Motion Detection
- ♦ Multiple Screen Display
- ♦ Signal Noise Ratio
- ♦ Survellance Vechicle
- ♦ Three-dimensional (3D) design in CCTV & Security
- ♦ Transmission of Video Signals by Cable
- ♦ Transmission of Video Signals by Remote Methods
- ♦ Transmission of Video Signals by Fibre Optics
- ♦ Video Analysis
- ♦ Wireless CCTV
Digital Technology & Recording
Recent developments have made it possible to store video images on magnetic discs, as on a computer hard disc. This is done by converting the image to a digital form to store it. The early problem was that to obtain reasonable resolution required storing a massive amount of data. The result is that only a limited number of images could be stored. A reasonable quality colour picture with a resolution of 681 x 582 pixels has 396,000 picture elements. This would need about 1/3 megabyte (Mb) of disc storage.
Modern digital compression technology now means that many more images can be stored. There are now systems that can store thousands of images. Even this must be considered in the light of the quality of image and the amount that can be stored. For instance, real time video is presented at the rate of 25 frames per second, i.e. 90,000 frames per hour. A 100-Mb hard disc would store 330 frames, which is only 13 seconds of video at normal density. A compression of 2:1 still only stores about 26 seconds of live video. Sampling every other frame would double this again but it can be seen that digital storage has a long way to go before replacing the video recorder. Having said this, technology in this field is advancing at a very fast rate and is the obvious way forward.
Digital recorders are available but their use is a tiny fraction of that of analogue video recorders. This is no surprise as a videotape costing a few pounds can store over 432,000 high quality colour images, using a recorder costing a few hundred pounds. To store the same number of pictures digitally is very costly both in storage media and hardware required to write to it.
The primary successes of digital recorders have been in event recording, where fast recording and search makes digital recorders most attractive. Many digital recorders include multiplexers as the timebase corrector required for digitising means that comparatively little extra circuitry is needed to add this feature, which helps to make them cost effective.
This was the original introduction to digital recording in the second edition published in 2000 and would have been written in about 1999. Technology has moved on at a fast pace since then. In fact it is now at the stage where digital recording is virtually the norm with the use of analogue VCRs declining rapidly.