Pros and Cons of HDcctv in Video Surveillance Applications
Alf Chang | Date:
As video surveillance migrates to IP, HDcctv is offering a midway point for users with existing investments. Alf Chang, a&s consultant, discusses the benefits and setbacks of the HDcctv approach.
HDcctv cameras, which we will refer to as HD-SDI cameras for their transmission type, are all the rage in security. Complete product lineups popped up at major trade shows this year, generating global buzz. As part of our camera test, we tested 19 network cameras and six HD-SDI models. With more camera options than ever, we were interested in the performance of HDSDI, combining coaxial transmission with high-definition resolution.
The Viewpoint feature looked at network megapixel cameras and how they depended on components to perform. HD-SDI cameras also depend on robust components to stand out, which we examine in this Tech Corner feature. More importantly, we will look at how practical HD-SDI solutions are for real-life use.
The six surveyed HD-SDI cameras used image sensors roughly the same size as network camera sensors. For now, most camera manufacturers prefer to use CMOS image sensors from Sony, Micron, OmniVision and Panasonic.
HD chipsets can transmit up to 270 Mbps, 1.485 Gbps and even 2.97 Gbps over a 75-nanometer coaxial cabling solution from Gennum. Other popular chipsets are from UFINE and Nextchip, each with an HD image signal processor (ISP) for video surveillance. So far, there are five ways to transmit SDI signals. The first is over coaxial parallel YUV inputs, with an FPGA converting the analog signal into an SDI one. This method is older, but the rise of the ASIC has made this an obsolete option few manufacturers choose.
The second way to transmit SDI signals also uses parallel YUV inputs, with an ASIC converting the analog signal into SDI. This method is adopted by more manufacturers because ASICs tend to be more stable.
A third way involves LVDS YUV inputs that convert the analog signal into SDI over an FPGA. This requires additional cost and is preferred by Japanese manufacturers.
The fourth method directly streams HD BT.1120 signals from the ISP's module to the SDI chip. This is preferred by manufacturers who deploy an ISP with their image sensors.
Finally, the fifth method uses a WDR image sensor, which is combined with an FPGA and SDI chip to stream HDSDI signals. However, some vendors found this method interferes with WDR exposure levels, resulting in flicker. This is a problem we noticed in multiple camera models that were entered for our test. From the six HD-SDI cameras we surveyed, there are relatively few component choices and applications. However, the earliest members of the HDcctv Alliance are choosing image sensor ISPs and camera modules not just from Sony, Micron or OmniVision, but from newer HDcctv members such as Pixim and Conexant.
For HD-SDI transmitter chips, Stretch and Gennum were among the first to offer options. New HDcctv Alliance members include Nextchip, Grain Media, Hisilicon and UFINE, which mean the number of HD-SDI offerings will increase and command more attention.
HD Performance Benchmarks
It was interesting to note that the components for the HD-SDI cameras were virtually identical. Most of the SDIcompliant components were brand-new, with a limited range of options. This made it was difficult to distinguish between the cameras, as seen in Image A.
One thing that was clear was progressive HD-SDI signals were best for display. During tests, these components performed consistently, maintaining good color saturation and distinct color differences, as seen in Image B.
Day-night performance did differentiate some cameras from the rest, even if they used the same sensor and ISP. Similar to the network camera test, the cameras looked markedly different with backlight compensation (BLC) and WDR switched on, shown in Images C and D. Differences between BLC and WDR should be noted by installers during the procurement stage.
Prime Time for HD?
We included HD-SDI cameras in our testing, based on the number of offerings available from Korea and Taiwan. What we did not know at the time was the amount of interest outside of Asia, with American and European brands treading the HD waters.
One observation about the HDcctv Alliance is that it could threaten network camera growth, but could also become a last resort for analog manufacturers on the brink of becoming obsolete. This depends on how the HDcctv standard performs and whether analog providers are willing to work together more closely. Regardless of the outcome, HDcctv applications will be the next trend.
Present sales are weak, since there is limited back-end support for HDcctv cameras. However, as more manufacturers launch HDcctv-compliant storage devices and transmission products, HD solutions are likely to see higher uptake in the future.
Our test sought to find out whether HDSDI solutions are viable today. Many analog video manufacturers have started to offer HD-SDI cameras, which offer HD detail. However, are these mature solutions and is there an application market for them?
Intersil's Security Link over Coax (SLOC) technology enables transmission of IP and analog signals over a single cable. This would allow a network megapixel camera to use the same cabling system with analog cameras to transmit images up to 500 feet. SLOC offers a much-needed cabling alternative for network cameras, as they continue to face environmental challenges.
As HD-SDI launches continue, they satisfy demand for a midway solution between analog and IP. The migration to IP gives HDcctv the breathing room it needs to develop.
HD cctv adopts a broadcast transmission medium as the basis for HD development. As the signals are uncompressed, there is no image lag or TCP/IP protocol issues. The completeness of the HD-SDI transmission standard offers a high resolution plug-and-play camera that works on any HD display. The development of HD makes it a serious competitor in the face of megapixel's biggest advantage: Detail.