HD CCTV has been with us for a while now, but we need to be careful the issue is not clouded by pure resolution. Image quality and image rates are extremely important factors in choosing a CCTV system.
Early HD cameras often used technology derived from webcams and as such had poor image processing, they concentrated more on the IT functionality than the image processing often giving poor low light reproduction and high noise content in the image.
With an increase in both processing power and image sensor quality, streaming real time HD CCTV images is now a realistic option, this has enabled the introduction of full function dome cameras delivering HD images and enabling almost real time control with little or no image data lag.
Conventional CCTV, in the UK is based on the PAL video system, this standard is almost as old as television itself, with all the image date combined onto a composite signal image resolution is naturally restricted by the transmission bandwidth limitations of the cables and the PAL standard.
A PAL image is made up of 2 interlaced images (fields) each restricted to 288 visible lines and typically 600 lines vertically, these fields are combined to create a frame, each field takes 20mS to arrive and motion blur often occurs between fields causing a blurred image when the video is paused.
PAL resolution is there for restricted by the standard (576x600) 345,600 pixels (typical) or in modern terms 0.345 Megapixels. To make matters worse the majority of older analogue recorders will only record one of the 2 fields, this is to stop motion blur during replay, but has the effect of halving the resolution. Most modern analogue CCTV recorders though record all the fields. Various image size standards have come into being since we started recording digitally.
Because HD CCTV is IP based (over a computer network) the CCTV images are already in the correct format to be recorded to hard disk, the number one benefit is the recorded image can finally be an exact copy of the original live image. A note of caution though there are many recorders on the market that will either only record when motion is detected or record at lower resolutions than the live displayed image. This methodology is used to save hard disk usage and cost.
Modern HD cameras,1.3 Megapixel upwards, are not restricted by the limitations of the PAL format, two main benefits are, the image resolution can now exceed the limitations pf the PAL format and secondly and often missed is the ability to do frame transfer capture and instantly capture the whole image rather than the two fields, this gives a crisper still image at full resolution.
The visual look of an image, the colour content, noise reduction systems, contrast and exposure control to an extent can be a personal choice. CCTV cameras need to operate in a wide range of changeable lighting conditions and a camera that can adapt to the changing environment is worth the extra investment. The lens is the front end of the camera and its performance affects everything after. The image sensor can only work with the image passed by the lens, the better this is the less work the sensor and image processing electronics need to do. The light passing properties of the lens are extremely important, the ability to remain in sharp focus when the iris is fully open, lens coatings and response to different light spectrums (colours).