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3.5
Image processing
Three features that may be supported in network cameras to improve image quality are back-
light compensation, exposure zones and wide dynamic range.
3.5.1 Backlight compensation
While a camera’s automatic exposure tries to get the brightness of an image to appear as the
human eye would see a scene, it can be easily fooled. Strong backlight can cause objects in the
foreground to be dark. Network cameras with backlight compensation strive to ignore limited areas
of high illumination, just as if they were not present. It enables objects in the foreground to be seen,
although the bright areas will be overexposed. Such lighting situations can also be handled by
increasing the dynamic range of the camera, which is discussed in section 3.5.3 below.
3.5.2 Exposure zones
Besides dealing with limited areas of high illumination, a network camera’s automatic exposure
must also decide what area of an image should determine the exposure value. For instance, the
foreground (usually the bottom section of an image) may hold more important information than
the background; for example, the sky (usually the top section of an image). The less important
areas of a scene should not determine the overall exposure. In advanced Axis network cameras,
the user is able to use exposure zones to select the area of a scene—center, left, right, top or
bottom—that should be more correctly exposed.
3.5.3 Wide dynamic range
Some Axis network cameras offer wide dynamic range to handle a wide range of lighting condi-
tions in a scene. In a scene with extremely bright and dark areas or in backlight situations where
a person is in front of a bright window, a typical camera will produce an image where objects in
the dark areas will hardly be visible. Wide dynamic range solves this by applying techniques,
such as using different exposures for different objects in a scene, to enable objects in both bright
and dark areas to be visible.
Figure 3.5a At left, image without wide dynamic range. At right, image with wide dynamic range applied.
CAMERA ELEMENTS - CHAPTER 3
