Quality Domes Hold No Viewing Limits Ⅰ
Editor / Provider: a&s International | Updated: 3/25/2011 | Article type: Tech Corner
What makes a dome good? A&S examines performance and installation issues to illustrate how fixed, speed and PTZ domes make the cut in an increasingly IP-enabled world.
Dome cameras are characterized by their distinctive bubbles, offering installers an extra option for demanding sites. They can be adapted for different applications, depending on user requirements and monitoring purposes.
Fixed domes are much like box cameras, except for a rounded form factor for easy installation and aesthetics. Mostly deployed for indoor surveillance, installers can adjust fixed domes for lens position, viewing angle and focus. Once the dome is installed, operators can only view a set area.
Speed and PTZ domes overcome the viewing limitations of fixed domes. They can monitor specific scenes or targets by size, position or both. Other uses for speed and PTZ domes include patrolling specific routes at a set time, or integration with intrusion detection for alarm verification.
PTZ cameras are not always housed in bubbles, offering more lens options and camera functions. However, they are usually larger, heavier and pricier than speed domes. As speed domes are housed in a single unit, they have a smaller form factor, more mounting options and greater pricing flexibility.
Ease of Installation
Regardless of dome type, the cameras must be easy to install. As most domes are suspended from ceilings or poles, they require installers to climb ladders, or utilize basket cranes or cherry pickers. This altitude limits the time and amount of tools installers can use placing the dome, which can be quite heavy, said Rich Huang , PM at EverFocus Electronics.
Installation is a two-step process for most domes. “Construction and industrial design affect performance,” said Alf Chang, Senior Consultant for A&S magazines and a former integrator. First, the housing is placed,and then the camera is fitted into the back box and enclosure.
The mount, or where the camera attaches to the back box, has a crucial effect on performance, Chang said. Metal mounts tend to be too rigid and cause too much interference. Plastic mounts can be too soft and loose, which may result in the camera dropping out of the mount and landing in the bubble. Understanding what materials a dome is made of can reduce maintenance calls.
Reliability is another benchmark of a good dome. “We look at good value for money, whether it's for the top-end, medium or budget applications,” said Andrew Pigram, Technical Director at Norbain. “But you can't sell rubbish to anyone.”
[NextPage]Fixed Dome Differentiators
Fixed dome selection looks at image quality, resolution, progressive or interlaced, and sensitivity, Pigram said. “Linked to those is whether you have a sophisticated DSP with noise reduction, which is related to performance.”
A dome's back-box construction will affect heat dissipation. “Too many ICs will overheat the camera and shorten its lifespan,” Chang said. Inferior materials will also cause interference, such as a bad lens connector, which should be inspected before purchase.
One way to infer how hot a dome might get is by looking at power usage. “Low power consumption is important to save power, but also for thermal operation,” said Jeff Corrall, Product Line Manager for Edge Devices, March Networks. “If you heat up a camera, it could malfunction. Or it may function properly, but its overall life cycle is reduced if the components are outside temperature specifications.”
A more prosaic benchmark is the dome's ability to lock position, said Ian Crosby, Product Marketing Manager for CCTV, Bosch Security Systems. The better the dome stays put, the better it will prevent shock and vibration effects.
A dome's processor determines its functionality. As chips have gotten faster and smaller, more features are now built into dome cameras, such as slow shutter, wide dynamic, Sens-up or digital noise reduction. “Some features are better on the edge, but they will depend on your computing power,” Huang said. “You need to select a faster or bigger CPU for analytics.”
A dome line may be divided into high-end and budget models by DSP. “Security is a relatively low-volume business, but requires many types of cameras,” Huang said.
Axis designs its own ASIC chip and this gives the company an edge in the market, said Erik Fr?nnlid, Director of Product Management, Axis Communications. Its processor features software for image correction, such as a corridor format that optimizes scenes that are more vertical than horizontal, such as hallways or tunnels. Modular designs and use of the latest technologies, as well as good forecasting and planning, allow Axis to source components in large quantities, which keeps prices manageable, Fr?nnlid added.
Samsung Techwin also has its own semiconductor foundry, using the same DSP chipset for its dome range. “We have ranges of both analog and network domes, including megapixel versions, arriving very soon,” said James Smith, European Marketing Manager.
Another deciding factor in dome selection is the image sensor. Whether the sensor comes with an image processor will affect image quality, along with the sensor 's format, Chang said.
Resolution and frame rate are considerations in sensor selection. “Low-light performance is also important,” Corrall said. Global shutter on CMOS chips has better image results compared to rolling shutter.
However, CCD sensors still outperform CMOS ones in most low-light conditions. “For image sensors for fixed domes, good low-light performance requires CCDs,” Huang said. “But as CMOS improves, that will change.”
To differentiate, some vendors develop their own image sensors, while making themselves less vulnerable to sourcing fluctuations from component suppliers. “We provide image sensors for both CCD and CMOS,” said Iida Atsushi, PM of Security Solutions, Business and Professional Products for APAC, Sony Electronics. Pan-tilt mechanisms are also made in-house, saving sourcing time; on the other hand, they add to development cost.
The line between CCD and CMOS is almost always drawn at resolution, with analog and network domes delivering different results. “An analog image is interlaced, so if an analog dome is connected to an encoder, you only see about 400 TVLs,” said Caroline Kuan, Marketing Specialist at DynaColor.“IP domes are at least 600 TVLs, which make a difference in image quality.”
True network cameras use progressive scan, Fr?nnlid added.