Zoom: less is more in the world of surveillance (Pt 1)

By Nafis Jasmani, Country Manager, Axis Communications Malaysia.

In many surveillance situations, being able to effectively magnify an image to reveal specific details is a necessity. Often, the small details that are picked up by a security camera are the most important; in criminal prosecution cases, for example, obtaining clear pictures of faces and clothing can affect the course of justice.

It is a common assumption that the higher the zoom factors of a lens, the better its ability to magnify a scene and make details more visible. This is not always true. In the world of security cameras, 18x zoom can be equal to 36x. More specifically, a high-resolution security camera with 18x optical zoom can provide images that, for surveillance purposes, are just as, or even more useful than those delivered by a standard resolution, 4CIF camera with twice the zoom capa¬bility.

Which has better zoom: 18x or 36x?
HDTV network cameras can easily fulfill demanding surveillance require¬ments using just half the zoom, demonstrating that what appears to be less can actually be more.

Compare the pictures below. Figure 1 shows a 36x zoomed-in view using a pan/tilt/zoom (PTZ) camera with 4CIF resolution (704 x 480 pixels). Figure 3 shows an 18x zoomed-in view using an HDTV 720p PTZ camera with a resolution of 1280 x 720 pixels.


The pixel resolution in both cases is virtually the same: the newspaper’s name, for example, is readable. However, the HDTV camera offers the same details with just half the zoom capability of the standard-resolution camera.

It is also important to note that the HDTV camera’s wider (16:9) field of view makes it possible to moni¬tor a larger area without compromising image details. In the image from the 4CIF camera (Figure 1), only one person can be seen in the picture, while in the HDTV image, the operator can see more than one person and simultaneously pick up small details such as texts on the newspaper. So while the level of detail is similar, the HDTV 720p camera enables more of a scene to be seen, which is advantageous in surveillance situations. The wider field of view in zoomed-in mode also makes tracking easier and more reliable since the risk of losing sight of a person or object while panning or tilting the camera is reduced.