HDTV/Megapixel: Excellent Image Detail
HD/megapixel technology enables network cameras to provide higher resolution of video images than analog CCTV, i.e. the ability to see more details or have a wider coverage – a key consideration in video surveillance applications. With an HDTV or megapixel network camera, the resolution is at least three times better than an analog CCTV camera.
Combining HDTV/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.
HD/megapixel surveillance
HD and megapixel network cameras have an important role to play in video surveillance applications. They can provide images that are more useful, with more image detail and with wider coverage than standard resolution cameras. Depending on your requirements, Axis network cameras can bring the advantages of HDTV, megapixel and network technology to your surveillance application.
| Format | Resolution (pixels) | Aspect ratio | Image scanning |
| HDTV 720p | 1280×720 | 16:9 | Progressive |
| HDTV 1080p | 1920×1080 | 16:9 | Progressive |
The variation of requirements within video surveillance is enormous. However, it can be boiled down to 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 HDTV/megapixel network camera or a number of non-megapixel network cameras.
High detail
These are the 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 enable a closer view of the area of interest, or by placing the camera close to the area to be monitored. Using a HDTV or 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 704×480 pixels (NTSC) or 704×576 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 75 pixels per foot in good conditions, or even 150 pixels per foot in challenging conditions. See also the standard EN 50132-7:2012 by CENELEC www.cenelec.eu. 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 1,050×1,050 pixels, which is slightly more than 1 megapixel.
To assess which network cameras you need (megapixel, HDTV 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.