Video Compression
There are two major video compression algorithms used in Network CCTV Cameras:
MJPEG - A stream of compressed still images (JPEG) is sent from the ip cctv camera to the viewing or recording device.
MPEG-4 - Single compressed images are sent at regular intervals to the viewing or recording device. Between these images, a stream of data is sent which identifies the changes between frames and the moving picture is re-constructed.
| Feature | MJPEG | MPEG-4 |
| Bandwidth | Relatively high. | Relatively low. |
| Data Storage Requirements | Relatively high. | Relatively low. |
| Computing power required to view and record images | Relatively low. | Relatively high. |
| Data Integrity (and evidential confidence) | High - still images are directly available from the system. | Low - still images have to be re-constructed. |
| Additional Software Requirements | No additional software is required to view still and moving images in standard tools (eg Internet Explorer, Firefox) | Additional CODECs (Coder/Decoder) are required and are usually chargeable. |
| Recommended for: | Security Applications | View-Only Applications |
Some network cameras are available as either standalone MJPEG or MPEG-4, others are selectable on configuration to be one or the other and a few top-end cameras offer simultaneous broadcast using both algorithms.
A third algorithm (H.264) is starting to become available on some cameras - this is an extension of MPEG-4 and has similar advantages and disadvantages.
Video Sensor
There are two types of Video Sensors commonly found on Network CCV Cameras:
CCD: Charged Coupled Device
CMOS: Complementary Metal Oxide Semiconductor
| Feature | CCD | CMOS |
| Colour Definition | Sharp Colour Definition | Soft Colour Definition |
| Colour Accuracy | High | Medium-Low |
| Lighting Conditions | Can operate in a very wide range of lighting conditions. Can adapt quickly to changes in lighting conditions - see also lenses. | Requires good lighting conditions. Slow to react to changes in lighting conditions. |
| Ranges of lenses | Full range of lenses available. | Limited range of lenses available. |
| Price | Typically more expensive | Typically less expensive |
| Recommended for: | Any location | Indoor, well-lit locations. |
Lens Type
Most network cameras have either Board-Mount or CS-Mount lenses.
Board-Mount lenses are smaller and are generally push-fit and of a fixed focal length. They are normally interchangeable, but this requires a certain degree of skill and patience.
CS-Mount lenses are larger, screw-fit and have a much wider range of facilities. They are generally very easy to change. There are two features of CS-Mount Lenses which are important when choosing a network camera.
Auto-Iris: These lenses automatically adjust the size of the lens aperture to match lighting conditions. The camera can then adapt very rapidly to a wide range of lighting conditions. Auto-Iris lenses should be used outdoors or in variable lighting conditions, eg a shop-front. Auto-Iris lenses can only be fitted to cameras which have this facility.
Vari-Focal: Vari-focal lenses have an adjustable zoom so that the angle of view can be adjusted to suit the installation position to give an idea field of view. They should not be confused with (much more expensive) auto-focus zoom lenses which can be controlled by software.
An Auto-Iris, Vari-Focal Lens adds about £50 to the price of a camera, but adds considerably to the functionality and flexibility of the installation.
Lens Size
The horizontal field of view (HFoV) and the Vertical field of view (VFoV) are the angles viewed by the camera. This depends on 2 variables, the size of the video sensor and the focal length of the lens. Typical combinations give the following approximate results (actual results depend on other variables as well, eg screen size, software):
| Lens Focal Length (mm) | ¼" Sensor | 1/3" Sensor | ||
|
| HFoV (deg) | VFoV (deg) | HFoV (deg) | VFoV (deg) |
| 3.6 | 54.4 | 42.5 | 76.4 | 53.1 |
| 4.0 | 49.6 | 38.6 | 61.9 | 48.5 |
| 4.5 | 44.7 | 35.6 | 56.1 | 43.6 |
| 6 | 34.3 | 26.3 | 43.6 | 44.3 |
| 2.8~12.0 vari-focal | 66.9~17.5 | 53.1~13.3 | 81.2~22.6 | 65.6~17.1 |
| 12.0~30.0 vari-focal | 17.5~7.1 | 13.3~5.3 | 22.6~9.2 | 17.1~6.9 |
