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
Video Compression
As the CCTV industry continues to move towards digital devices, such as Digital Video Recorders (DVRs) and IP devices, technicians need to be familiar with the subject of Compression – the methods such as MPEG, Wavelet™, and similar. In this article we spell out some of the basics of compression technology.
So first – why is data compression necessary? Because without it, the volumes of data produced by digitising CCTV image streams would swamp the available storage and communications systems.
To overcome this, the process of compression is applied to the image stream, reducing the amount of information that needs to be transmitted and stored. In fact compression of the camera signal is not new - many people do not realise that all ‘analogue video’ has always been compressed.
Similarly, there has long been a need for data compression in the computer industry. Specialist mathematicians have worked for many years on solving the basic problem of how to reduce the image size to produce the best compromise between image clarity, the data size of the image, and the amount of processing power it takes to run the compression method.
Different applications have different priorities regarding clarity of the image, data volumes, and processing power – for example identification evidence has a different picture quality requirement compared to monitoring the length of a queue. So if you are selecting digital equipment, you’ll need to select the compression format that suits the network or the application you are installing.
Different sorts of compression are described as lossless or lossy. In general, the less compression the better the playback and recorded image, so naturally in that sense lossless is always better than lossy; however, less compression means more data to be transmitted and stored, and thus incurs higher system costs.
Compression reduces the signal in three ways. The first is by various mathematical tricks that are lossless to the image, and can be reversed at the time of display so that the full image is viewed. The second is to remove parts of the signal that are redundant to human viewing of the image. The third method is to start to visibly reduce image quality – definition, frames per second, and colour range – and it is this type of compression that is called lossy.
The compression formats used in CCTV vary by manufacturer and by product. But the four most commonly used compression formats are:
* H261
* Motion JPEG, also written M-JPEG or M-JPG
* Wavelet
* MPEG, also written mpg