Video Transport: The Composite Conundrum
Composite video – analogue systems and devices – has served the video surveillance sector well over the years. There are still a high number of career criminals serving time because of composite images! It might be fashionable to knock composite solutions, but is such criticism justified, and does the technology have anything left to offer?
[dropcap]C[/dropcap]omposite video has been a mainstay of surveillance-based security systems for decades, and over those years the performance generally improved. Many of the advances have been driven by cost reductions, and in the latter years by processing developments. In truth, the performance hasn’t changed much in recent times. Instead, additional features and functions have been introduced to smooth over some of the technology’s inherent rough spots!
When video recording moved from magnetic tape to digital drives, the result was an ability to record video at resolutions higher than 220 TV lines! This saw mainstream cameras advance from what was then the standard 330TVL mark. Technologists, experts and manufacturers still debate whether the true top resolution of composite video is 480TVL, 520TVL or any of the other figures bandied about. In truth, it matters not; composite video streams have got as good as they’re going to get.
When considering composite video in the modern world, there is a need for some basic honesty. Of course, this works both ways. Often, composite video isn’t as black as some would have it painted; that said, it’s certainly not the future either!
Whilst the security industry spends a lot of time (too much time in fact) debating the pros and cons of various technologies, often the customer is less concerned about ‘how’ their system works. All they want is video of the required quality, and the ability to process that video as necessary to achieve their goals. To think that end users are demanding IP video or HD-SDI, or composite video for that matter, is a nonsense. Instead they have a wishlist with regards to performance and functionality, and it is the job of installers and integrators to deliver systems to meet those expectations.
With this in mind, the question shouldn’t be how networked technology, HD-SDI or any other solutions compare with composite, but what – if any – benefits composite video offers that place it as the best choice for an application.
What about 960H?
Much has been said about 960H resolution analogue video, and comments range from open and honest specifications, through to the misleading, with many hovering between the two extremes. This middle ground can be confusing, because whilst claims contain factual information, they don’t always give all of the information!
In essence, 960H is wide screen analogue video. Image size is 960 x 576 pixels, whilst standard D1 is 720 x 576 pixels. Note that the vertical pixel count is the same in both formats. The fact that it is wide screen video has led some to intimate that 960H is another format of HD video, which it is not! It should be noted that 960H video does not share HDTV’s 16:9 aspect ratio; it is actually 5:3. That said, it will display correctly to the eye on 16:9 displays.
As is often the case, the fact that a camera uses a 960H chip does not automatically mean it will deliver the same performance as all other 960H units. The CCD itself is just one element, and the manufacturers’ processing engines will have a bigger impact on quality.
So, how does 960H stack up? The diagram shows the difference in the various resolutions; it is very important to understand what this diagram represents. The HD formats offer a 16:9 aspect ratio, while 960H offers a 5:3 aspect ratio. All three images will display full-screen on any appropriate monitor that is used. However, the size differences in the diagram represent the number of pixels in an image of each format. Therefore, if a larger number of pixels are displayed on the same monitor, the detail will be finer, and the quality will be higher.
Essentially, with regard to resolution, 960H falls short of HD720, and significantly short of HD1080 video. However, 960H is an analogue format, and is backwards compatible with existing D1 devices. That said, if you want to add 960H to an existing system and enjoy the wider aspect ratio, this will require upgrades. Any DVR will need to be upgraded to a 960H compatible unit, and 4:3 displays will also need to be upgraded. Because standard definition lenses are ground to tolerances acceptable for 4:3 D1 images, it will be best practice to either use megapixel lenses, or at the very least to use trading up principles to ensure quality is preserved at the very edge of the image.
Because of this, many see 960H as an investment which doesn’t always stack up.
One function often cited when considering composite video is low light performance. It was true that when digital devices first appeared in the video surveillance sector, they struggled with regard to low light performance. To be honest, they also struggled with delivering high quality real-time images as well!
Alternatives to analogue video have been constantly developed over the years, and many digital devices can compete with composite models, and in some instances can outperform them, with low light performance.
Whether quoted for composite video or digital video, sensitivity figures of 0.X lux, or the ever more popular 0.0X lux type numbers, are a nonsense for real-world use. Often such figures use slow shutter (great if you want to watch a static scene, but beset with motion blur if activity takes place), or don’t deliver a full video signal, or have certain processing functions fully turned up to force a measurable signal despite the settings making the image unusable.
Benchmark compared performance from a number of composite day/night cameras. These had to deliver real-time blur-free and relatively noise-free footage, allowing colour fidelity and image quality to be preserved. For the leading brand composite cameras tested, the required switching point to night mode was between 6 and 4 lux. Below these levels, the image degradation image was considered as a compromise by our test team.
When attempting the same test with some unbranded and budget-end cameras, the figures rose to between 12 and 8 lux!
On a like-for-like basis, using digital cameras with 4CIF or D1 chips (note that there is a difference between cameras with higher resolution chips which have been configured to deliver 4CIF or D1 streams), there wasn’t a significant difference, although the digital units did need to be switched 1 or 2 lux earlier. Units with CCDs performed marginally better than those with CMOS sensors.
Where a fairly significant difference did occur was when composite cameras were compared with HD or megapixel devices. The reason for this has to do with pixel density and size.
Both CCD and CMOS sensors work by converting the light that falls onto them into electrons. The accumulated charge of each pixel is then measured (each sensor works in a slightly different way), and these measurements determine the value of the individual pixels. In order to provide a clean and accurate image, an appropriate amount of light must fall onto the sensor.
If you consider a D1 camera chip, it contains just over 400,000 pixels. In effect, this means that the surface of the chip is divided up into 400,000 picture elements. Sufficient light must fall onto each one to create a strong signal, every time a frame of video is created.
The size of the picture elements affects the low light capabilities of the camera, which is why 1/2 inch sensors are better performers in low light than 1/3 inch versions!
With this in mind, consider that a full HD camera has around two million picture elements on the same size chip as the D1 camera. Because the pixel density is so much higher, image detail is greatly enhanced. However, because every pixel is significantly smaller than with a D1 chip, this means there is less surface area to gather the light. As a result, low light performance is inferior.
As with anything, there is a trade-off. The difference in low light performance isn’t straightforward, because you’re not comparing similar performance. If you want higher resolutions and enhanced quality, then low light performance will suffer slightly.
Benchmark has tested a wide range of HD cameras, and the average lowest light level in which a real-time blur-free and relatively noiseless image could be achieved was between 14 and 9 lux. A few HD cameras with very good low light management achieved between 8 and 5 lux.
In reality, most well-implemented systems should switch at a realistic level, long before colour or image detail suffers any degradation, and additional illumination should be utilised to preserve image quality!
Two of the often quoted benefits of composite video are that systems are easy to implement, and some devices can be low cost. It is important to realise that unless the system achieves each and every goal of the customer, and fully meets their expectations, then ease of installation and trade price should never be reasons for specifying a lesser solution!
Of course, the ease of implementation of analogue systems is something of a double-edged sword. Whilst the installation of an average mainstream system using composite technology is not greatly challenging, it can be significantly slower than with other more advanced options, purely because of the amount of cable that needs to be fitted. Also, where new cabling is installed, the customer must be offered choices so that the infrastructure can – if required – be used for other technologies should an upgrade be desired at a later date.
Consideration should also be given to the scalability and flexibility on offer, and sadly this is where composite-based designs can be found wanting. As customers become more aware of the flexibility on offer from remote video streaming, distributed archiving, video sharing, analytics and other processing options, so they will expect such functionality from a system. Rather than informing a customer that systems can do these things, the tide is changing to a point where it could be argued that the real requirement is that end users must be informed that composite systems, where specified, cannot offer certain features and functions.
Installers and integrators must ensure that any solution – and this applies equally to video, access control, intruder detection, perimeter protection, automation, life safety or any other offered system – delivers what end users (who are increasingly better informed) consider as ‘reasonably expected’ from such an investment.
Even where a system is delivered as per specifications, and satisfies the immediate needs of the customer, any regret concerning the specification at a later time will create negative associations with the entire experience. It is therefore critical that care is taken to ensure that composite video is specified because it can do the job required, and can also satisfy any potential future needs too. Otherwise, compromise will be the only outcome.
One point that must be made before any conclusions are drawn is that we are not about to see the death of analogue systems, no matter how much those who sell other options might like to claim we will! That said, we will see its gradual decline, and that decline will be accelerated where end users are looking for flexible, scalable solutions that add value and deliver tangible benefits.
Increasingly, composite video will be used for applications where the bare essentials are all that is required, or where the budget is negligible. There will always be those who seek a simple-to-fit and low-cost solution, even if it means having very basic functionality. Despite attempts to breathe new life into the composite sector, it must be accepted that the technology has limitations, with regard to performance, flexibility and functionality.
The limitations will see prices continue to fall, but that in turn can only serve to devalue the associated systems in the long run, and the market will – as happens with all disrupted technological markets – enter an inevitable spiral which will see it become ever harder for professionals to afford to deliver high levels of service and support.
Today, where composite systems still exist, it makes sense to maintain performance until the user decides to upgrade. However, implementing new systems based on composite video, or replacing equipment to enjoy a new ‘flavour’ of analogue technology, makes little sense.
Delivering solutions is predominantly about meeting the customers’ expectations. Any compromise, either to simplify an installation or to save a few pounds, could affect the overall performance of the solution, and may damage your reputation as a result!