Video surveillance expert John Honovich on when PTZs are needed versus when a megapixel surveillance camera can take the place of a PTZ
[Editor's note: John Honovich publishes this and other information on network video at IPVideoMarket.info.]
Though popular, PTZ cameras often create a false sense of security. They make for great demonstrations but are often underutilized or misused.
The use of PTZ cameras varies significantly. Offices and fast food restaurants rarely use PTZ cameras. However, the majority of cameras at shopping malls and public surveillance are PTZs. In general, PTZs are the standard choice for monitoring large public areas.
Advantages of PTZs
- Monitoring large areas: the PTZ camera can be pan, tilted and zoomed to cover hundreds of acres (a few square kilometers). This is not possible with fixed cameras which normally only cover a small area (few hundred square meters).
- PTZs can be placed on tours (patterns) that move the camera in a predetermined way to capture areas of interest. For instance, over a 1 minute period, the camera can capture the front door, the gate to the parking lot and the fenceline. The tour can repeat indefinitely.
- Operators can control PTZ cameras to track a suspect or respond to a security incident. The operator can zoom in to view and capture fine details like facial features or license plate. The operator can also follow a suspect across a large area.
- Because PTZs can cover a wide area, this reduces the cost of coverage per given area.
- People love PTZ demos. They are the closest thing the surveillance industry has to movie special effects (see the demo above). It makes people feel excited about the potential.
Disadvantages of PTZs
- PTZs can see and record only where they are currently looking. While the PTZ has a potential to view enormous areas, at any given time, it only covers the area of a fixed camera. If a PTZ on a tour is looking at the front door and an event happens at the vehicle gate, that event is missed (and vice versa).
- Service issues: Since PTZs are complex mechanical devices, they tend to have much more frequent service calls and shorter live spans (compared to fixed cameras).
- High storage costs: Because PTZs move so frequently, their storage utilization tends to be 2 - 4x higher than a fixed camera with equivalent frame rate and resolution. Motion based recording cannot be used (or it has little savings since the camera continues to move). Plus, encoding motion requires higher bit rates to maintain image quality.
- Poorer image quality: PTZ image quality is often poorer than fixed cameras, especially when zoomed in. This is likely a result of smaller chip sizes (1/4" for PTZs vs 1/3" inch in fixed cameras) and the much larger focal lengths in PTZs (over 50mm focal length is common for professional PTZs).
- Mispositioning of PTZs is common. Operators routinely place (or leave) the PTZ in different positions. While this can be solved by using a 'home' functionality, many systems are not configured to use this properly.
- Works Poorly over IP Networks: Controlling mechanical PTZs are very sensitive to latency. If the latency is more than a fraction of a second, controlling PTZs become very difficult. This is not an issue for traditional analog systems but a growing problem for IP video. Furthermore, network viewing often requires on screen PTZ controls which are much harder for an operator to use. These issues can be somewhat rectified by using USB joysticks and manufacturer optimizations to reduce latency. However, this is a frequent problem with IP networks.
- Higher Per-Camera Cost: Whereas a fixed camera may cost $200 - $500, a PTZ camera with a 15x or greater zoom can cost $1,500 to $3,000. The cost increase is significant.
- The demos are unreflective of most real applications. While it's impressive to see a building a mile away, that ability rarely solves real security problems for users.
In general, PTZs suffer from a host of logistical problems that detract from the potential appeal in demos.
Alternatives to PTZs
Megapixel IP cameras are emerging as an alternative to PTZs but issues remain.
The primary potential of Megapixel cameras is to eliminate the problem that PTZs can only view/record where they are currently looking. By contrast, since megapixel cameras use a digital zoom, viewing does not impact the area recorded. Also, since megapixel cameras eliminate the mechanical complexity of PTZs, their cost is lower (even for multi-megapixel) and the service issues should be less.
However, megapixel cameras cannot come close to matching the potential coverage area of a PTZ camera. Even with the far higher pixel count of a megapixel camera, it's unlikely to provide anything more than the equivalent of a 2x or 3x optical zoom. Furthermore, while megapixel vendors contend that megapixel cameras provide the resolution of 20 to 60 standard definition cameras, the effective image detail is nowhere close to this (especially at lower light conditions).
While megapixel certainly offers enhanced resolution and coverage area over fixed cameras, there's little reason to believe that megapixel cameras can fully eliminate the use of PTZs.
Best Fits for PTZs
With these considerations in mind, PTZs work best when:
- An organization has operators dedicated to monitoring security systems. If you are a big box retailer or a sports stadium and have operators dedicated to monitoring, PTZs make sense. The PTZ cameras allow operators to monitor greater areas. However, if you rarely monitor the security system and primarily use it for investigations, megapixel cameras are a worthwhile alternative to consider.
- An organization has a really large area that needs to be covered. Such large areas may still be impractical even with megapixel cameras. Only a PTZ provides you the range needed (so long as you have active monitors). However, if you have a moderate size area (like a parking lot with a few dozen spaces), one or two megapixel cameras are likely to be less expensive and more effective.