Axis P-Iris Quick reference guide

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P-Iris.
New iris control improves image quality in megapixel and HDTV network cameras.

Table of contents
1. Introduction 3
2. The role of an iris 3
3. Existing lens options 4
4. How P-Iris works 4
5. Redening video quality 6

3
Introduction
The introduction of megapixel or HDTV xed 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 benets megapixel cameras but all xed 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 eld. In short, P-Iris means improved image sharpness and increased image usability for net-
work video surveillance operators.
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 eort 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 aects 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 eect on image sharpness and depth of eld. Depth of eld 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 eld while a smaller opening increases it. Having good depth
of eld 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 eld—where objects at dierent 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.
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4
3.
While it is true that a smaller iris opening often means sharper images, too small an opening may blur an
image due to an optical eect called diraction. This problem can be seen in bright outdoor situations
when a camera closes the iris too much and light is diracted or spread over many pixels. The smaller
each pixel is on an image sensor, the more of a problem diraction becomes as the diracted light
aects more pixels. This can typically happen in cameras that use an automatic DC-iris lens in combina-
tion especially with megapixel sensors that have small pixels. (While a megapixel sensor has more pixels
than a standard VGA 640x480 image sensor, the size of each pixel on a megapixel sensor is often
smaller than the size of each pixel on a VGA image sensor.)
Fig. 2 This illustration is an example of the depth of eld for dierent size iris openings, expressed as f-numbers. A smaller iris open-
ing, that is a larger f-number, enables objects to be in focus over a longer range. Depending on the sensor’s pixel size, very small
openings may cause image blur (diraction).
Existing lens options
Until the introduction of P-Iris, the types of iris control on lens options for xed surveillance cameras
have been xed, manual and automatic. Fixed iris lenses have no ability to adjust the iris opening. With
manual iris lenses, the iris opening must be adjusted by hand. Auto-iris lenses, either DC iris or video iris,
automatically adjust the iris opening in response to changes in light levels.
For indoor applications where light levels are constant, xed or manual iris lenses may be suitable since
there is no need to constantly adjust the iris opening.
In situations with varying light levels, for example, outdoor camera installations, the preferred lens option
is an automatically adjustable iris. This is commonly a DC-iris lens. A DC-iris lens responds only to light
levels and does not take into account the impact of the iris opening on other image qualities such as depth
of eld. With a DC-iris lens, the camera only knows if the iris opens or closes in response to the level of
light; it doesn’t provide the camera with information about the position of the iris. Without this informa-
tion, the camera is not able to eectively steer the iris opening in order to optimize image quality. This is a
drawback that P-Iris is designed to overcome.
How P-Iris works
P-Iris is a new type of iris control that is both automatic and precise. Unlike a DC-iris lens, the main task
of the P-Iris control is not to continuously adjust the ow of light through the lens. The primary objective
of P-Iris is to improve image quality by enabling the optimal iris position to be set so that the central and
best-performing part of the lens is used most of the time. This position, expressed as a specic f-number,
is where the lens performs optimally, where many optical errors are reduced, and where image quality
(with regards to contrast, resolution and depth of eld) is at its best. This is the default setting in a net-
work camera with P-Iris.
4.

5
When the whole lens surface area is used, maximum light reaches the image sensor, depth of
eld is shallow and the use of the full lens surface may create image aberrations.
When the central part of the lens is used, unwanted optical eects are reduced, good depth
of eld is achieved and image quality is optimized. This is the preferred iris position in a P-Iris
camera.
When the very center of the lens is used, diraction may occur, which results in blurriness.
Image quality will not be optimal since the resolution and contrast are low.
Fig. 3 This diagram illustrates the impact of setting the iris to use dierent areas of a lens surface.
Working in conjunction with P-Iris is the use of electronic means—gain (amplication of the signal level)
and exposure time—to manage slight changes in lighting conditions and to further optimize an image.
This allows the optimal iris position to be maintained as long as possible. In situations when the preferred
iris position and the camera’s electronic processing capabilities cannot adequately correct the exposure,
a P-Iris camera will automatically instruct the iris to move to a dierent position. In dark conditions, for
example, the iris will fully open. In bright situations, a camera with P-Iris is programmed to limit the
closing of the iris to a position that avoids diraction or blurring, as explained earlier. Hence, in all
lighting conditions, P-Iris can automatically make adjustments to deliver optimal image quality.
Old technology P-Iris
Fig. 4 Note the great depth of eld in the picture to the right taken by a P-Iris camera.
Old technology (cropped view) P-Iris (cropped view)
Fig. 5 Note the sharp contrast in the picture to the right taken by a P-Iris camera.

6
Redening video quality
P-Iris is an innovative solution that truly allows a network camera—particularly a megapixel or HDTV
network camera—to perform optimally in all lighting conditions. It enables the delivery of crisp, high-
resolution images with good depth of eld. It can also avoid diraction in bright situations. Furthermore,
it does it all automatically, which is highly valued in outdoor video surveillance applications.
Although the P-Iris control is initially available only in Axis network cameras, the technique has the
potential of becoming a new industry standard as Axis and Kowa have decided to make P-Iris accessible
to the whole industry.
P-Iris is a revolutionary development for video surveillance cameras and is a testament to Axis’ commitment
to providing the surveillance industry with superior video quality and greater image usability.
5.

www.axis.com
38023/EN/R2/1009
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About Axis Communications
Axis is an IT company oering network video solutions
for professional installations. The company is the global
market leader in network video, driving the ongoing
shift from analog to digital video surveillance. Axis
products and solutions focus on security surveillance
and remote monitoring, and are based on innovative,
open technology platforms.
Axis is a Swedish-based company, operating worldwide
with oces in more than 20 countries and cooperating
with partners in more than 70 countries. Founded in
1984, Axis is listed on the NASDAQ OMX Stockholm
under the ticker AXIS. For more information about Axis,
please visit our website at www.axis.com