Image quality, increased image resolution, greater camera and recorder functionality, ease of installation, reduced cabling costs and a vastly simplified set up are cited amongst the many benefits IP CCTV systems have over analogue ones. We asked Carl Hayesmore, technical manager at CCTV Center, the Panasonic System Networks Distributor, to explain these key benefits in more detail and, where possible, quantify the differences.
Many factors affect image quality in CCTV systems, but resolution is amongst the easiest to quantify. The greater the image resolution, or pixels per image, the more detailed the image appears and the better its perceived quality.
The maximum resolution analogue cameras offer is usually 720 x 576 pixels. This is known as D1 within the UK-based, PAL video standard. In practice, many DVRs record in lower formats such as CIF or 360 x 288 pixels, in order to reduce image data size for efficient recording and transmission. By comparison, IP cameras typically have a resolution of 640 x 480 pixels, which is just less than D1, but usually higher quality. However, the introduction of HD, Megapixel cameras with resolutions of 1280 x 960 pixels means IP camera resolutions can now be set at up to four times that of D1, with far superior detail as a result.
Electrical interference is probably the largest cause of poor image quality in analogue CCTV systems. The coaxial cables used between cameras and recorders are susceptible to the electro-magnetic fields generated by power cables and other sources. Interference causes unacceptable image faults like noise and flicker. These reduce the signal quality and eventually make the signal unusable. By comparison, IP CCTV systems transmit digital data which is either right or wrong and can often be corrected or even rebuilt during transmission.
Many analogue systems also quote a refresh rate of 50 fields per second using Interlace Technology to process the images. Interlace means alternate lines of each image are updated in every frame, rather than the whole image. This rate is somewhat misleading, as each field has only half of the vertical height refreshed every 1/50 of a second. The Progressive Scan technology used in Panasonic IP cameras updates the entire image at 25 frames per second. This increases image quality significantly, especially when recording movement and is immediately apparent in a demonstration.
Analogue to digital conversions
Image quality reduces with each analogue to digital conversion that occurs within a CCTV system. A modern analogue camera sensor produces an analogue image which is converted into a digital signal within the camera to allow for processing. The digital image is then converted back to an analogue signal and transmitted over coaxial cable. The DVR receives the analogue signal and converts it to digital for use in the DVR and for recording. This is converted back to analogue and fed out to a monitor, which in turn converts to digital for viewing on a standard flat-panel monitor.
An IP system, by comparison, takes the analogue sensor image and converts it to digital within the camera. This is compressed and transmitted as a digital signal to a DVR or NVR, for recording and system management. An NVR with a HDMI connection uses a digital signal for monitor viewing. In total, far fewer conversions occur over all, so image quality is higher.
Much of the functionality used to enhance analogue camera image quality applies equally well to IP cameras. Super Dynamic III (SDIII), which compensates for extreme image contrast; adaptive black stretch (ABS), which boosts dark image areas; auto image stabilizing, which removes shudder or vibration affects; auto back-focus, which ensures optimal camera focus and IR sensitivity for low light operation, are typical examples.
IP cameras use all these functions and have some significant, additional new ones. Face detection for use in biometric applications; adaptive compression or even variable resolution, where different parts of the same image can be recorded at different resolutions (e.g. using a lower resolution for sky than for buildings) all improve the image quality, recording and transmission efficiency of significant areas of interest.
IP CCTV can often be co-located on existing networks or, alternatively, be run on entirely separate networks. IP CCTV can utilise existing fibre optic, structured cabling and coaxial cables. These can, if necessary, be converted for IP CCTV (Ethernet) operation, meaning the opportunities to reduce cable installation time and costs are huge.
Power over Ethernet, where power and data for cameras are transmitted using the same cable, add a further benefit. Also, an installer no longer needs to cable from the camera back to an NVR in every case, but can connect to a network near the camera using PoE switch.
Another huge benefit of digital cameras is remote set-up. The installer no longer needs to be on-site, up a ladder adjusting camera settings, but can do it from the NVR or pc via a web browser. This opens up a multitude of remote management and maintenance business opportunities for forward thinking installers. Lastly, IP system flexibility and scalability offer further benefits, because extra cameras are simply added to a system when required, which takes significantly less time than a traditional analogue system upgrade.
CCTV technology is becoming increasingly IP-based for good reason. Not only are IP systems easier to use, install and set up, but they also have superior image quality, excellent scalability and save money over time. The benefits are irrefutable.