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What do digital PTZ cameras do?

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PTZ stands for Pan, Tilt and Zoom.

PTZ camera, when you pan and tilt you physically rotate the camera using electrical motors. The zoom is controlled by mechanically moving two lenses closer together or further apart dependent on whether you are zooming in or out with the effect that objects in view appear larger or smaller.

What do digital PTZ cameras do?

On a conventional PTZ camera, when you pan and tilt you physically rotate the camera using electrical motors. The zoom is controlled by mechanically moving two lenses closer together or further apart dependent on whether you are zooming in or out with the effect that objects in view appear larger or smaller.

Digital PTZ cameras don’t work in this manner. The camera will first capture a full image, usually in megapixel resolution. When a user decides to zoom in they are provided with a section of the overall picture. The pixels in this are then enlarged so that the cropped image is the same size as the original. This gives the appearance that you have zoomed in as objects are now larger.

DPTZ cameras vs PTZ cameras

Zooming resolutions

The first thing that people will notice when using digital PTZ features is that the quality. When zoomed in two times, image quality can be similar to PTZ cameras but the more you zoom in, the less definition you see on objects. After only a few zooms the object you are looking at will be almost unrecognizable.

The reason is that there is a finite limit on the data in an image. When zooming you cut down on the amount of information you are looking at and it is cut again every time you zoom. On a conventional PTZ camera the optical zoom always captures the same amount of information whether you are fully zoomed in or out.

When used in a security scenario this is less than acceptable. Say you monitor a thief coming into a bank who is just out of range to be identifiable. You zoom in with digital PTZ but the more you zoom in the less identifiable the person gets. In mission critical situations digital PTZ just doesn't cut it.

Reliability

As stated earlier, conventional PTZ cameras use motors to move the camera around. There are multiple different ways of using these to pan the camera such as bands, cogs or direct drive. There are even some which use electromagnetism to accurately aim the camera in some higher end cameras.

In whatever camera you look at, however, there are moving parts and as most people will know, anything with moving parts will eventually fail. Bearings can wear, motors can burn out and bands can stretch. As a result most manufacturers will recommend that to prolong the life of your camera you should limit its movement.

The same goes for temperature. The mechanics inside conventional cameras can freeze up if temperatures plummet. I have heard many stories of cameras in arctic conditions where the PTZ mechanism had frozen. When the users try to move the camera it essentially rips itself apart.

Similarly, strong vibrations or movements, such as on swaying ships or when mounted on tall poles in windy conditions, can cause the camera to slip. Every time a PTZ camera starts up it has to zero itself so that it knows where it is aiming. The camera will find its zero-location so that it knows how far it can move left, right, up and down. However, once it has zeroed itself any external forces which act on the camera will pull it away from where it thinks it is looking. As a result the camera will think it is looking at point A when it is really looking at point B. A restart will solve this problem by resetting the camera back to the zero position but there’s nothing to stop it from happening again.

Digital PTZ systems perform their functionality in software. As a result there are no moving parts and nothing to break, freeze or move. So long as the camera is functioning, the digital PTZ system will work. So from a reliability point of view, digital PTZ cameras win hands down.

After-event monitoring

PTZ cameras are used primarily to monitor a large area with only a single camera. However, say you have a conventional PTZ camera pointed at the entry gate to a site and someone scales the wall out of shot. The next day you come in to find all your stock has vanished and your security system has missed it completely. Conventional PTZ cameras are limited to monitoring where they are aimed.

With cameras such as the Mobotix Q24M-SEC you can now capture footage from 360° around the camera and digitally zoom in on certain areas. Because you are recording the entire field of view it doesn't matter if you are zoomed in on the entry gates or not, all angles are recorded.

Retrospectively wishing that your cameras were pointed in another direction is pointless. If you have a large area to cover then the limitations of a conventional PTZ camera can leave you very exposed. Second win to digital PTZ.

However, the Mobotix camera is a special case. Most cameras will only provide a 90 degree view at best. This will drastically limit the panning and tilting that can be performed.

Discretion

No one likes being watched. In commercial environments it can put people off buying items as they feel persecuted by having a camera pointed at them. In city locations it can even have an adverse effect with people acting out when they see that a camera is watching them. It is an unfortunate side effect of conventional PTZ systems.

With DPTZ cameras there is no way to see where the viewer is monitoring and there is no noise associated with movement. If placed in a discreet location most people won’t even know it’s there.

Can digital PTZ cameras really compete with conventional PTZ?

Unfortunately no. With security systems it always comes back to quality. The whole point of having a zoom is to capture higher detail of remote objects and if the system cannot provide that then there is no point in using it. The benefits that DPTZ offer over conventional PTZ do not outweigh the limitations in quality, with the possible exception 360 degree monitoring as covering blind spots can never be bad.

In order for digital PTZ systems to be truly comparable to conventional PTZ system the resolution and quality at full zoom needs to be identical. To achieve this you would need to make the image sensor large enough that when zoomed in both resolutions are the same, in the case of most PTZ cameras this would be 640×480. This would be completely unfeasible and with new megapixel PTZ cameras arriving shortly the gap between the two will only increase.

For the time being, however, digital PTZ is being marketed largely as an add-on feature to provide zoom on static megapixel cameras with very few being aimed as a direct replacement for PTZ cameras

 
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Article details
Article ID: 35
Category: Analog Cameras
Date added: 2014-10-02 05:05:03
Views: 1266
Rating (Votes): Article rated 4.8/5.0 (16)

 
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