Elevator Surveillance Guide

 Elevator Surveillance Guide

Installing surveillance in an elevator can be challenging. Small but wide areas, vandal resistance, and transmission methods all present challenges not found in other areas cameras are installed. In this note, we look at:

• Form factor: Box vs. dome vs. specialty
• Resolution: How much is necessary?
• Transmission: Wired vs. wireless vs laser methods
• Dealing with electrical contractors

Form Factor

The first decision to make when considering elevator cameras is form factor. Minidome and corner mount are the two most common options in use as they most compact compared to box, bullet, or full sized dome cameras. Other form factors, such as box or bullet may be more easily tampered with due to the low ceiling height of the elevators, and more easily knocked out of position.

Minidome

The key advantage to minidomes is camera choice, as most manufacturers offer cameras in this form factor, with numerous resolution and lens options. These options are not generally seen in corner mount cameras.

However, they are more obtrusive than many corner mount housings, and do not blend into the interior of the elevator as well. Where aesthetics are the key concern, domes may not be preferred.

Corner Mount

This type of mount places the camera in a roughly triangular housing made to cover one of the elevator's corners. Some are sold as unitized housing/camera packages, while other manufacturers sell housings meant to accept a box camera. Size and appearance varies depending on manufacturer:

They key drawback to corner mount cameras is limited availability. Most manufacturers do not offer corner mount options, and those that do typically only offer one or two models, with limited resolution and lens choices. Larger corner housings built for box cameras add more flexibility, but are larger and more obtrusive.

Field of View/Resolution

Given elevators' small size, generally under 10' wide, users typically choose to cover the full car instead of just the doors. This gives them not only the opportunity to view comings and goings, tracking subjects throughout a facitity, but to view potential incidents in the elevator, as well. However, care should be taken that pixels per foot (PPF) does not drop below acceptable levels for recognition if no other cameras will provide facial shots of subjects, e.g. lobby and hallway cameras.

For example, using an actual 103° field of view from an elevator camera with Camera Calculator, we can see the difference between VGA, 720p, and 1080p in a typical 8x8' elevator. Estimating ~9' to target to reliably capture subjects as they enter through the elevator doors, 720p provides 56 PPF in this scene. This is likely enough to provide identification quality video under good lighting. VGA provides only 28 PPF, too low for recognition, while 1080p provides 85, more than enough.

Mounting Height

Since most people look down while walking, and criminals may actively avoid cameras, mounting height in elevators should be carefully considered for the best chance of capture. As we found cameras are typically best mounted as low as possible, with ~8' being a "sweet spot", better able to see those with heads down or hats on while also see over subjects beneath the camera.

This image shows the effects of mounting height and the subject's face angle, displaying the difference in capture quality at various mounting heights with the subject's face level as well as tilted down.

Signal Transmission

Once the camera has been selected, installers must decide how signal will be carried from the elevator. There are three typical options for this:

• Traveler cable
• RF wireless
• Optical laser

Traveler Cable

Connections between the elevator car and the machine room for power and signal are made via a specialized traveler cable. This cable is attached to the car, typically to the bottom, and to the top or center of the shaft. The construction of this cable varies, but it typically contains multiple twisted pair conductors for power and control, and possibly a UTP or coaxial cable for video. 

This image shows cross-sections of various flat traveler cables:

Generally speaking, since these cables are often attached to the top of the shaft, making the cable approximately twice the height of the shaft, UTP is not a usable solution for Ethernet. Buildings of 12-14 stories can easily have a 300' traveling cable, which exceeds the maximum distance category cables can be run, before even considering horizontal runs to an equipment room or IDF. In low-rise buildings, UTP may be an option, however. Fiber-optic and coaxial cables may be considered otherwise.

RF Wireless

The second option is to opt for wireless connectivity, utilizing a pair of wireless APs between the car and bottom or top of shaft. Both are used in practice, with the bottom of the shaft generally chosen for easier servicing. In this case, local power must be obtained from the car, which may involve the elevator contractor. Power is readily available, however, due to lights and air conditioning installed in the car.

Wireless eliminates the issue of necessary conductors in the traveler cable, but presents challenges of its own. Cables and conduits located in the elevator shaft may cause interference, making wireless connectivity unreliable. Very narrow beamwidth antennas may be used to compensate for this, but antenna alignment must be carefully set and maintained over time.

Optical Wireless

Optical wireless uses a pair of laser transceivers, one mounted to the car, the other in the shaft, to send/receive data. This is specified to handle elevator shafts up to 75 floors.

Optical product performance is degraded by dust, dirt, and other debris which may fall in the elevator shaft and as such should be cleaned regularly.

Dealing With Elevator Contractors

Normally, most facilities maintain service contracts with an elevator contractor, since the elevator must undergo routine maintenance. These contractors may be difficult to deal with, as a number of users have shared. They are often hesitant to modify existing traveling cables for new services, simply because it complicates (however slightly) their routine maintenance of the elevator with a system outside their control. If the traveling cable is insufficient to add video, installing a new cable is, most times, cost prohibitive, and may remove the elevator from service for several days. Both of these add up to expenses users may not wish to incur.

To avoid the coordination and expense required to have the elevator vendor add video to a car, users and integrators may attempt to add their own cable to the car. There are two things to be aware of in this case: 

• Third parties attempting to modify the cable without the contractor's permission will void warranties and service contracts in most cases. Even leaving existing cables alone and simply zip-tying a new UTP cable to it may be frowned upon.
• According to NEC code, hoistway cables must be listed for use in these applications, and be of type E. Standard UTP, fiber, and coaxial cables do not meet these requirements.

 

RAW Formats

RAW Format implies that there is no compression done on the image. The major types of RAW format are RGB, YUV, YIQ. Our eye is more sensitive towards light intensity variation than color variation. So loss on color information will not affect the over all quality of the image. RGB is an end stream format. Information from the image sensor is in RGB format and we need the same format for displaying the image on an end

device. YUV & YIQ formats are developed for Analog TV transmission (NTSC & PAL respectively) and the digital version of YUV, YCbCr is the most common format used for image and video compressions.

Conversion from one format to another is described below:

RGB to YCbCr Conversion

Y = 0.299 R + 0.587 G + 0.11B

Cb = 0.564 (B - Y)

Cr = 0.713 (R - Y)

YCbCr to RGB

R = Y + 1.402 Cr

G = Y – 0.344 Cb – 0.714 C r

B = Y + 1.722 Cb

Y – Luminance Signal

Cb, Cr – Chrominance Signal, Color difference signal

R – Red

G – Green

B – Blue

Need for Compression

Consider an image of resolution 640 × 480. Let us calculate the size of the picture in RAW format. Each of the 10 Color is represented by 8 bits. Then for each pixel it needs 24 bits. Total no of pixels in the image is 640 × 480 = 307200 pixels. Therefore the size of the image turns to 307200 × 3 bytes = 921600 bytes. But an image in compressed format with the same resolution takes only 100 KB.

In the case of RAW video stream of length 1 sec its needs 640 × 480 × 3 × 25 = 23040000 bytes (23 MB) of storage if the frame rate is 25 frames/sec. But it’s known that the VCD format video having a size 700 MB plays for around 80 minutes. In the former case we need 110400 MBs (23 MB × 60 × 80) as storage space for 80 minutes video. Therefore we can achieve a high compression 150: 1 at the cost of computational complexities.

Which Image Quality is Better

When thinking about maximizing image quality, resolution is usually the first thing that comes to mind. However, resolution is not the only factor that impacts quality. The amount of bandwidth available and used can have a dramatic impact on image quality. In this report, we examine bandwidth and the effect that it has on quality across numerous cameras.
Which Image Quality is Better?
To better understand image quality, let's start by examining two samples of the same scene side by side:

 

Consider two questions:

1. Which camera has higher resolution? A or B?

2. Which camera is better? A or B?

It is pretty obvious that the image from Camera B is better so this should be a simple case.

The reality is that those images are from the same camera at the same resolution and frame rate (720p/30). All that was done to the camera was changing the Constant Bit Rate target from 512 Kb/s to 8 Mb/s.

Factors Impacting Quality:

Even with the same resolution, two common settings impact quality: 

1. Bit Rate: Most cameras can have their bit rate adjusted to specific levels (e.g., 512 Kb/s, 2 Mb/s, 8Mb/s, etc.) 

2. Quantization Level: Most cameras can have the level of compression adjusted (often called a quality or compression setting with options from 1-10 or 0-100)

Typically, these are mutually exclusive. If you lock in bit rate, the camera will automatically adjust the quantization level to not exceed the bandwidth set. Vice versa, if you set the quantization level, the camera will automatically change the bandwidth consumed to make sure the quality / compression always stays at the same level.

Our Test Process

We wanted to better understand how changes in these two factors impact video quality. To do so, we did a series of tests with three HD cameras: the Axis P1344, the Sony CH140 and the Bosch NBN-921.

For the bandwidth tests, we tested each camera at the following levels:

• 512 Kb/s
• 1 Mb/s
• 2 Mb/s
• 4 Mb/s
• 8 Mb/s

We did this across a series of scenes to see how quality would vary in different conditions:

• Daytime Indoors (300 lux)
• Nighttime Indoors (.5 lux)
• Daytime Intersection

Finally, we did a similar series of tests varying the quality level of a VBR camera (the Axis across 0, 30, 60 and 100 levels) to better understand changes in quality and bandwidth consumption.

Capturing Crystal Clear Images With Megapixel Technology

Megapixel surveillance is not a new concept — its applications and benefits are starkly clear. What has changed are smarter cameras, taking advantage of the added pixels and a better understanding of illumination in real life. In the first of a two-part report, A&S examines how smarter megapixel cameras are getting; the second part looks at best practices for optimal performance.

The big picture for megapixel surveillance cameras looks bright, in the wake of the recession. HD and megapixel cameras are expected to make up nearly 30 percent of network camera shipments in 2011, according to IMS Research. By 2015, it is forecast that more than 60 percent of network cameras shipped will be of megapixel resolution.

The resolution increase has a noted effect on the whole surveillance system. While a 2.1-megapixel or 1,080p HD image is six times larger than a D1 image, the additional pixels require a bigger pipe to transmit more data. The infrastructure and storage costs for megapixel are well-documented, with ROI and TCO being used as arguments in favor of bigger pictures. The fate of megapixel is linked to the future of IP networks, with HD forecast to make up most high-resolution cameras compared to megapixel, according to IMS.

Megapixel surveillance requires careful planning, but the benefits of added resolution boost the accuracy of analytics. Edge devices take advantage of faster processors, resulting in smarter use of pixels. Analytics can help reduce bandwidth, as an event will trigger video streaming, rather than constantly sending the same still images over the network. A more distributed architecture puts less strain on networks and makes life easier.

Clarity is the main driver for megapixel. “At the end of the day, you're putting in a security system to protect life and provide evidence in a court of law,” said Stephen Moody, Security Development Manager for ViS Security Solutions, an integrator in Ireland.

Cracking the Code
H.264 is the de facto standard compression for megapixel cameras, due to its efficiency in crunching large data files into smaller ones for transmission and storage. As compression evolved from M-JPEG's stills to MPEG-4 and now to H.264, a variety of profiles yield differences in performance. With 17 profiles in all, three are the most common: baseline, main and high, said Sachin Khanna, PM for CCTV, Bosch Security Systems.

By profile, the baseline is appropriate for video conferencing; the main profile is good for broadcast video; and high profile is most applicable for HD broadcast video. “H.264 requires a fair amount of processing power for encoding and decoding; this may limit the camera's frame rate and dictate the NVR platform to achieve the desired performance,” said Rich Pineau, CTO of Oncam Global.

Most H.264 profiles stem from 2-D applications, with not all profiles being capable of integration. “Even if both cameras are H.264 and the manufacturers are partners, the system could still not work,” said Patrick Lim, Director of Sales and Marketing for Ademco Far East. “The I/O and output are hard to integrate. Some engineers say it's easy to plug and play — there's no such thing.”