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Dispelling the myths of IP video: Myth #10: Networked video image quality is not as good as analogue

In this series, Roy Alves, country manager of Axis Communications South Africa, examines 10 myths about IP video.

The basis of this myth originates from the fact that CCTV cameras have been on the market for a longer period of time, as opposed to network video cameras, which made their grand entrance in 1984. It is assumed that because of this timelapse that network video image quality is lagging behind the CCTV offering.

Quite the contrary, network cameras have the same, in some cases even better, high-quality image sensors (CCDs) and optics as analogue security cameras. In a recent discussion with the South African Police Service a detective mentioned that they do not even look at CCTV surveillance footage in the investigation of a crime - simply because of the poor image quality.

Image quality is clearly one of the most important features of any camera, if not the most important. This is especially true of security surveillance and remote monitoring applications, where lives and property may be at stake. Unlike traditional analogue cameras, network cameras are equipped with the processing power not only to capture and present images, but also to manage and compress them digitally for network transport.

Image quality can vary considerably and is dependent on several factors such as the choice of optics and image sensor, the available processing power and the level of algorithms in the processing chip.

Today, two different techniques are available to render video; interlaced scanning and progressive scanning. The technique selected will depend on the application and purpose of the video system and particularly whether the system is required to capture moving objects and to allow viewing of detail within a moving image.

Interlaced scan-based images use techniques developed for cathode ray tube (CRT)-based TV monitor displays, made up of 75 PAL (phase alternating line)/480 NTSC (National Television System Committee) visible vertical lines across a standard television screen. Interlacing divides these into odd and even lines and then alternately refreshes them at 25/30 frames per second. The slight delay between odd and even line refreshes creates some distortion or 'jaggedness'. This is because only half the lines keep up with the moving image while the other half wait to be refreshed.

Interlaced scanning has served the analogue camera, television and VHS video world very well for many years, and is still the most suitable for certain applications. However, now that display technology is changing with the advent of liquid crystal display (LCD), thin film transistor (TFT)-based monitors, DVDs and digital cameras, an alternative method of bringing the image to the screen, known as progressive scanning, has been created.

Progressive scanning, as opposed to interlaced, scans the entire image line by line every 25/30 of a second. In other words, captured images are not split into separate fields like in interlaced scanning. Computer monitors do not need to interlace to show the picture on the screen. It puts them on one line at a time in perfect order. So there is virtually no 'flickering' effect. As such, in a video surveillance application it can be critical in viewing detail within a moving image such as a person running away.

Furthermore, by employing video servers, an analogue specialty camera or those that are already installed can be incorporated into an IP-surveillance system. In comparing network and analogue cameras, we must emphasise 'good' quality network cameras built for professional use. These high quality professional network cameras should not be confused with lower-end network or PC Webcam cameras used for 'Web attraction'. These cameras cannot deliver the same capabilities as a full-function network camera.

Network cameras and IP-Surveillance technology are delivering superior image quality by means of mega-pixel resolution. Analogue cameras are limited by the 0,4 Megapixel resolution of NTSC/PAL standards, which network cameras are not.

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