Advertisement
1.
Introduction
The introduction of megapixel or HDTV fixed network cameras
has meant greater resolution images but not always better
image quality. Maintaining image sharpness, particularly in
varying outdoor lighting conditions, has proved challenging. It
is a problem that has highlighted the limitations of existing
lens alternatives and the need for a better solution.
Axis Communications' search for a solution has now led to the
introduction of a new and revolutionary precise iris control,
P-Iris.
P-Iris not only benefits megapixel cameras but all fixed network cameras. The system optimizes the iris
opening under all lighting conditions and the result is images with better contrast, clarity, resolution and
depth of field. In short, P-Iris means improved image sharpness and increased image usability for net-
work video surveillance operators.
2.
The role of an iris
The P-Iris system involves a new approach to looking at the role of an iris and is the result of a joint
development effort between Axis Communications of Sweden and the Japanese lens manufacturer
Kowa.
The system comprises of a P-Iris lens and specialized software in the camera. The software steers a
motor in the P-Iris lens, enabling automatic and precise control of the iris opening. The key to under-
standing P-Iris is to look at how the iris affects image quality.
The iris of a lens regulates the size of a lens' aperture or opening and the amount of light that passes
through it so that an image can be correctly exposed. Without an iris, an image can become too light in
a very bright environment, or it can be dark if the lens opening is not big enough to let available light in.
The size of the iris opening also has an effect on image sharpness and depth of field. Depth of field refers
to the distance in front of and beyond the point of focus where objects appear to be sharp simultane-
ously. A wide iris opening reduces depth of field while a smaller opening increases it. Having good depth
of field is important in many surveillance applications as it allows more of a scene to be clearly visible.
It is particularly useful in the video monitoring of, for example, a long corridor or parking lot. Image
sharpness generally improves with a smaller iris opening because optical errors can often be reduced. All
lenses create some form of image aberrations when the full lens surface is used.
Fig. 1 Having good depth of field—where objects at different distances from the camera are in focus simultaneously—is important
in many surveillance applications as it allows more of a scene to be clearly visible.
3
Advertisement
