Axis Megapixel Network Cameras
Megapixel technology enables network cameras to provide higher resolution of video images than analog CCTV, i.e. the ability to see details and to identify people and objects – a key consideration in video surveillance applications. With a megapixel network camera, the resolution is at least three times better than an analog CCTV camera.
Combining megapixel network cameras with a selection of non-megapixel network cameras that are optimized for other needs (such as powerful optical zoom, extreme light sensitivity or low cost) creates video surveillance installations that are effective, reliable and cost-efficient.
What do you need to see?
Megapixel network cameras have an important role to play in video surveillance applications. They are obviously more suitable for some areas than for others. The determining factors are ultimately the requirements of the individual customer’s system. Once the specific objectives for each network camera in the surveillance application are set, the right type of camera can be selected for the best fit.
Naturally, the variation of requirements within video surveillance is enormous. The most fundamental question, however, is generally a choice between two different priorities:
General overview
In this case, the aim is to obtain a general overview of a scene. In a shopping mall, for instance, your primary goal of a camera installation may be to watch for the presence of people and view their movements—not the identification of individuals. Or you may want to see whether a parking lot is full or has empty spaces, rather than identify individual cars or read license plates. For overview applications, sufficient resolution and coverage of a scene may be achieved with a single megapixel network camera or a number of non-megapixel network cameras.
High detail
These are the really demanding situations where you need to be able to identify persons or objects in a scene. This could be point-of-sales monitoring where it is necessary to clearly see every item a customer is purchasing, or situations where you need to be able to identify a face. High detail images can be achieved by installing a network camera with a telescopic lens or a lens with zoom capability to allow a closer view of the area of interest, or by placing the camera close to the area to be monitored. Using a megapixel network camera in all such cases will provide even higher resolution images with more details than a non-megapixel network camera.
Pixels per foot – best practices
A conventional CCTV camera providing 4CIF resolution offers a resolution of 704x480 pixels (NTSC) or 704x576 pixels (PAL) after the signal has been digitized in a DVR or a video server, which corresponds to a maximum of 400,000 pixels.
In the surveillance industry, some best practices have emerged regarding the number of pixels required for certain applications. For an overview image, it is generally considered that 20 to 30 pixels are enough to represent one foot of a scene.
For applications that require detailed images, such as face identification, the demands can rise to as much as 150 pixels per foot. This means, for example, that you want to be able to strongly identify people passing through an area that is seven feet wide and seven feet high, the camera needs to provide a resolution of 1,050x1,050 pixels, which is slightly more than 1 megapixel.
To assess which network cameras you need (megapixel and/or non-megapixel, including pan/tilt/zoom cameras) it is important not only to do the calculations as outlined, but also to survey the location to determine the number of interest areas, the size of these areas and whether they are located close to each other or spread far apart. Other considerations should also be taken into account; for example the availability of guards performing live monitoring, the need for light sensitivity, bandwidth and storage.
