Over the last decade, the CCTV industry has seen a major shift from analogue to digital networking solutions for surveillance applications. In the next few years, the industry will bear witness to the adoption of High Definition (HD) IP video into mainstream CCTV systems, thereby mirroring the transition in consumer electronics.
For HD IP cameras to be adopted by mainstream video security applications (and the managers of same), the issues associated with high data rates and storage need to be solved. Those issues are currently being addressed with the recent launch of HD IP cameras boasting low data rates.
The advantages of HD IP cameras have been well documented. In summary, the three main areas where they can provide real benefits are general surveillance, forensic detail and digital PTZ. In terms of general surveillance, a single HD megapixel camera can replace several standard 4SIF cameras, thereby reducing costs. An HD megapixel camera is able to see more detail in the same field of view or view a wider field of view at the same level of detail.
When it comes to forensic detail, many existing analogue CCTV systems simply don’t provide enough resolution or quality for forensic evidence. Megapixel cameras solve many of these quality/resolution issues. They are ideal for applications where the system wants to identify and record faces, vehicle licence plates or certain objects.
As far as digital PTZ issues are concerned, HD megapixel cameras can digitally zoom quicker and with greater detail than analogue cameras while still recording the whole picture for later analysis. This provides superior performance and reliability for the end user.
All manner of CCTV installations may benefit from HD technology, but at present typical applications for HD IP cameras would include retail Point-of-Sale, banks, casinos, car parks, building entrances, military installations and city centre monitoring schemes.
Technology hurdles to overcome
In order for HD megapixel cameras to be adopted for mainstream use, the current technology hurdles have to be overcome.
Megapixel cameras require a higher resolution lens than ordinary CCTV cameras to maximise the picture quality. These lenses are readily available but are expensive in CCTV mounts, although this will change with the higher volumes from mainstream adoption.
Also, megapixel cameras use the same CMOS image sensors as employed in still digital cameras, whereas analogue cameras typically use CCD sensors. This is likely to change with the adoption of sensors from the HD TV/video industry. A higher density of pixels on the same sized sensor means there is less light falling on each pixel. Each pixel has less sensitivity and needs more light while the ‘noise’ in the sensor has a larger impact because it’s a higher percentage of the signal.
This is why first generation HD IP cameras typically had a worse low light characteristic than analogue cameras. However, sensor technology is improving quickly, with significant R&D resources now being focused in this area.
Arguably the most important factor to consider with its impact on network bandwidth and storage requirements is video compression. HD megapixel cameras are unlikely to be adopted for mainstream use until low bandwidth camera designs are readily available. This is now starting to happen with the launch of HD IP cameras harbouring superior compression capabilities and, hence, much lower data rates.
The scale of the problem
H.264 is the latest video codec (compressor and decompressor) standard, which follows on from the highly successful MPEG-2 and MPEG-4 video standards and improves on both video quality and compression.
Many of the current one and two megapixel HD cameras use MPEG-4 compression, resulting in higher video data rates. For HD to become usable in mainstream CCTV applications, though, H.264 compression technology needs to be deployed in the camera so as to provide the lowest possible data rates. However, not all implementations of the H.264 standard deliver the same quality of compression.
The data rates from different manufacturers’ cameras can vary significantly, even when comparing cameras implementing H.264. What of the typical data rates for a single one megapixel camera monitoring a fairly static scene such as a building entrance? The typical data rate for best compression technology would be <1 Mbps, with the approximate storage required for 30 days at 15 frames per second (fps) continuous recording standing at 0.5 Tb. For average compression technology, typical data rate is 5-6 Mbps with 3 Tb of storage.
The huge disparity in camera performance makes a significant difference in the cost of an HD CCTV solution. Using cameras with data rates of less then 1 Mbps means that HD IP cameras can use standard networks and storage and be cost-effective for everyday CCTV applications.
Data rate requirements
It’s very important for system designers and end users to know exactly the data rates and storage requirements for particular HD IP cameras in order that performance and costs may be fully understood.
However, some of the actual data rates are so high it’s not surprising these figures are often hidden and difficult to determine. Take a look at a typical datasheet for a 1.3 megapixel camera from a mainstream manufacturer and you will see the camera has a frame rate of up to 30 fps. However, nowhere is there a mention of how good the compression is (in other words, what the typical data rate is, and how much storage is required to record a stream from that camera)!
Some CCTV manufacturers are forced into using local storage because their HD IP camera bandwidth is such that it cannot reasonably be streamed live across the network. This somewhat negates the distributed and scalable benefits of IP video. By removing the high bandwidth problem, designers are free to choose a truly distributed architecture, placing storage wherever the best system design dictates it should be – whether that’s in a central location, distributed close to the camera or a fault-tolerant redundant configuration mixing the two.
The key, therefore, to the adoption of HD CCTV into mainstream surveillance is the ability to develop low bandwidth HD IP cameras. The three main elements that make up such a camera are the use of a true IP camera solution, excellent implementation of H.264 and dedicated hardware architecture. A true IP camera completely eliminates any analogue signal by connecting the digital signal processor present in all analogue cameras directly to the compressor chip. This ensures no added signal noise is introduced.
There are three common compression standards used in current HD IP cameras, namely MJPEG, MPEG-4 and H.264. Video is compressed using two types of frames: I Frame (also known as the Index or Key Frame and which contains the whole image) and P Frame, which only contains the information that’s different from the previous frame.
MJPEG only uses I Frames, whereas MPEG-4 and H.264 use a combination of both I and P Frames and, consequently, considerably less bandwidth than MJPEG. H.264 will require up to 50% less bandwidth than MPEG-4 to transmit the same quality image.
The H.264 standard specifies a set of optional tools which can be used to compress video. A compliant decoder must implement every tool, whereas a compliant encoder can choose which tools to use. This means there may be a big difference between encoders from different suppliers – some compress well, but not all.
Searching for some motion
To determine what information is transmitted in a P Frame, the image has to be searched for motion in each frame. The quality of the compression depends on how far and how well the search is completed on each frame.
Compared to the best encoders, a poor encoder design could result in a higher bandwidth for good quality video, increased bandwidth during high motion, dropped frames or ‘blocky’ or blurred video.
Due to the huge processing demands of a low bandwidth HD IP camera using H.264, it’s essential that the compression engine is implemented in dedicated hardware such as Field Programmable Gate Arrays (FPGA). Thanks to this type of design, low bandwidth HD compression can be achieved with a guarantee of no dropped frames.