Digital or analogue CCTV? The choice is yours, but there are many factors to be borne in mind when making your decision. I suspect that most of you reading this article will immediately start to think of the recording media, but any comparison of the two technologies goes much further than this.
As a company, Panasonic has a vested interest in both analogue and digital technologies, of course, so what we can offer the end user is a clear understanding of where we see the formats sitting in the marketplace by application.
Like other systems providers, we’re currently working on developing products to meet the demands of the new broadband networks now available, and are trying to envisage just how these systems will work in the years to come. However, the reality is that coax cable is still the best medium for delivering real, live and uncorrupted video images at a reasonable cost.
Yes, it would be true to say that Ethernet, LAN or WAN, ADSL, ATM and the good old ISDN have their place, but when considering them as the main backbone for a system they also have their drawbacks.
Keeping conversions to a minimum
Using this as your ‘start point’, if you want to get the best out of your coax system, the overriding factor is to keep the number of digital-to-analogue and analogue-to-digital conversions to a minimum. This helps in keeping the data as close to the original data captured by the cameras as possible. Every time you convert the data from digital to analogue, and run it over a cable network, you’ll lose information and degrade images.
Nowadays, nearly all cameras are digital, which means that they process information captured on the charged coupled device (CCD) digitally. This enables system provides to really sharpen the images that the CCD provides from 480 TV lines for colour or 570 TV lines for monochrome. These numbers are central to this discussion, so keep them in mind.
With digital processing ‘at the camera’, manufacturers can also offer end users improved functionality, such as so-called ‘super dynamic range’, to overcome difficult lighting conditions. This would not be possible with traditional analogue cameras. At the end of the processing, the camera then transfers the data back to analogue and places it on the coax cable.
Depending on the size and scale of the system you want installed on site, it’s at this point that your particular CCTV road meets a major junction. For larger systems you’ll generally need a matrix switcher. At the moment those available are nearly all based on analogue technology, but there are a few network-style switchers appearing. There’s even talk of such things as virtual matrices.
Once past the matrix (or if you have a smaller system where you don’t need one), end users are faced with a choice. Either you purchase a multiplexer and a traditional VHS or S-VHS VCR, or you try one of the many new digital recorders on offer.
Many of the currently-available digital recorders come complete with built-in multiplexers, which helps to cut down on the numbers of conversions needed in the system. Some digital recording products are single channel only, such that they must be used with a conventional multiplexer. Don’t be fooled again, though – multiplexers are digital too! They process the information by once again converting the analogue signal from the camera or matrix digitally before one more conversion back to analogue and then sending it on to the recorder.
The real difficulty comes when trying to generalise around digital recording. With so many different media and compression techniques currently on the marketplace, there is no real clear format leader as yet. That’s why groups like the Police Scientific Development Branch and associations such as the BSIA are trying to get the key manufacturers together to discuss these issues and find a way forward.
Good advice for the end user is to choose a manufacturer that will be around long enough to support your investment in the years ahead.
Choosing digital or analogue
Analogue recording is by no means dead in the water. As a major manufacturer of VHS and S-VHS recorders, we at Panasonic have charted an ongoing rise in volume sales for this part of the CCTV market.
In practice, VHS delivers 240 TV lines for colour, while S-VHS can offer you 400 TV lines of recording. This is still very good, and comes at a fraction of the cost of most of the reasonable quality hard disk products currently available. It’s easy to maintain, most existing end users trust the technology and the police know how to handle the evidence produced.
Most importantly, you can store a good deal of video information on a tape at a relatively low cost. What you do require, though, are reliable security officers able to run a proper and thorough tape management regime.
One easy step on from the traditional VHS or S-VHS recorder is the digital tape recorder. At this point, the end user must begin to question what he or she really wants from their CCTV set-up. If your main goal is simply a better picture quality then digital tape could well be the solution for you.
Now, though, you’ll start to question why you might need a non-linear method of recording, such as DVD or hard disk. Well, in just the same way that you might prefer CD and DVD to tapes in the car on the way to work, non-linear formats are all about flexibility and speed. End users are able to ‘jump around’ the recordings, possibly saving hours in search time when compared to analogue systems.
There’s no need for tape management here, it’s much easier to upgrade the software and such systems can easily be expanded if and when necessary. Not only that, to keep the local police happy you can give them a portable media recording such as DVD or CD.
Next comes the use of the Ethernet interface to transfer information from one end of the country to another. Just like you send attachments to people on e-mail, you could easily send pictures or video clips to the police or other interested parties. This Ethernet capability means that any authorised security manager is able to review the information stored on any disk from any location.
You can archive material to tape, but then why have a hard disk product given that you’ll still suffer from degradation issues as the tape heads wear out and the tape thins?
