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P-Iris - The replacement of DC-iris (Cover Story by Kowa & Axis Communication) |
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 Precise iris control for optimized performance in all lighting conditions P-Iris is jointly developed by Axis Communications of Sweden and Kowa Company of Japan. The new product was introduced at the Ifsec security tradeshow in Birmingham, UK in May 2009. It was highlighted in connection with the introduction of Axis P1346 Network Camera. Kowa will be producing a series of megapixel P-Iris lenses. Axis plans to introduce P-Iris in upcoming network cameras, beginning with the 3-megapixel AXIS P1346 Network Camera. Kowa and Axis expects other camera and lens manufacturers to also adopt the P-Iris technology to make it a standard that eventually replaces DC-iris lenses.
The function of an iris The ability to control a lens’s iris opening plays an important role in image quality. An iris is used to maintain the optimum light level to the image sensor so that images can be sharp, clear and correctly exposed with good contrast and resolution. The iris can also be used to control the depth of field. Iris control can be fixed or adjustable. Adjustable iris lenses can be manual or automatic (auto iris and P-Iris). An iris in a lens has a similar function as the iris in the human eye. It controls the amount of light that can pass through the lens to the image sensor so that an image is correctly exposed. The size of an iris opening plays a critical role in determining image quality. If too little light passes through, the resulting image will be dark or blurry from too much gain being applied. If too much light passes through, the resulting image will be overexposed. In addition, a smaller iris opening also produces an image with better depth of field (objects are in focus over a longer distance), and with increased sharpness because optical errors are reduced. Too small an iris opening will blur an image due to diffraction.
A P-Iris lens uses a stepper motor that allows the position of the iris opening to be precisely controlled. A P-Iris lens works together with software in the network camera to automatically provide the best iris position for optimal image quality in all lighting conditions. The software is configured to optimize the performance of the lens and image sensor. A DC-iris lens uses a galvanometer motor that is controlled by the image light level. A DC-iris lens relies on the camera to sample the video signal to control the iris opening. Why there was a need to develop P-Iris? An iris should be automatically and precisely controlled in order to optimize image quality in a variety of lighting conditions. In particular, the company wanted to make improvements in three areas:
Why there was a need to develop P-Iris? An iris should be automatically and precisely controlled in order to optimize image quality in a variety of lighting conditions. In particular, the company wanted to make improvements in three areas:
- Performance of megapixel/HDTV cameras that use sensors with smaller pixels,
- Ability to avoid blurring (diffraction) in bright surveillance environments
- better depth of field.
- Prior to P-Iris, lenses with an adjustable iris were either manual iris or auto iris lenses.
A manual iris lens allows a user to manually turn a ring on the lens to open or close the iris. This is not convenient in environments with changing lighting conditions, such as in outdoor applications. An auto iris lens can be a DC iris lens or a video iris lens. Both have a motor-driven, automatically adjustable iris opening that responds to changes in light levels. Both also use an analog signal (often analog video signal) to control the iris opening. The difference between the two is where the circuitry to convert the analog signal into motor control signals is located. In a DC-iris lens, the circuit resides inside the camera; in a video iris, it is inside the lens. In bright situations, a camera with an auto iris lens (especially one that uses megapixel sensors that have small pixels) can be affected by diffraction and blurring when an iris opening becomes too small.
Further more the ND-Filter concept (Neutral Density Filter) for DC-lenses is a built-in feature for the purpose of helping the diaphragm function toward the minimum aperture range. However this additional filter will negatively effect the resolution.
The problem with an auto iris lens is that it does not enable the camera or the user to know the exact position of the iris opening, which is needed to optimize image clarity.
What is P-Iris? P-Iris is a precise iris control that allows fixed network cameras to deliver better image quality in both indoor and outdoor applications. P-Iris, which involves a P-Iris lens and specialized software in the network camera, can automatically and precisely regulate the iris opening to enable better contrast, clarity, resolution and depth of field. Having good depth of field—where objects at different distances from the camera are in focus simultaneously—is important in the video monitoring of, for example, a long corridor or parking lot.
In bright situations, P-Iris limits the closing of the iris to avoid blurring (diffraction) caused when the iris opening becomes too small. This can typically happen in cameras that use DC-iris lenses in combination with megapixel sensors that have small pixels. Furthermore there is no ND-Filter incorporated into the lens for better resolution. Being able to avoid diffraction and at the same time benefit from an automatically controlled iris is highly valued in outdoor video surveillance applications. The advanced iris control will be especially beneficial for megapixel/HDTV cameras and demanding video surveillance applications. P-Iris is a revolutionary improvement for video surveillance cameras and for the industry in general. It allows fixed network cameras to reach a new level of performance in image quality. It is expected to replace DC-iris lenses as the standard iris control for fixed network cameras.
P-Iris is beneficial for megapixel/HDTV network cameras
A megapixel/HDTV camera uses a megapixel image sensor (an image sensor with 1 million or more pixels), which generally has smaller pixels than a standard resolution camera. A smaller pixel has a lower ability to gather light than a larger pixel. Therefore, the image quality is more dependent on getting the right levels of light into a megapixel/HDTV camera. P-Iris helps optimize the performance of the lens and image sensor to automatically adjust the iris opening for optimal image quality. If the iris closes too much in bright situations, a megapixel camera can lose resolution, causing blurriness. P-Iris limits the closing of the iris to avoid this situation and enables a megapixel camera to maintain the delivery of crisp, high-resolution images, even in difficult lighting situations.
Future of P-IrisP-Iris is expected to replace DC iris as the standard iris control for fixed network cameras. The technology used in P-Iris lenses is well known to the industry and it will take other companies between 6 and 12 months to incorporate P-Iris.
ProfileKowa Company, Ltd. was founded in 1894. Since its establishment, Kowa has grown into a multinational Japanese company actively engaged in various manufacturing and trading activities in the fields of pharmaceutical, textiles, opto-electronics and various consumer products. Kowa has been producing high quality lenses for 60 years including CCTV lenses. Kowa is continuously developing innovative products for the fast changing CCTV market. [www.kowa.eu]
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