67 GM&HuronValleySchools

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Dave Doerr has been involved in FRC since January 2007 as a software & controls mentor for Team 67, the HOT Team. Beginning in January 2009, he is also team leader for the HOT Team. Dave, along with wife Pat, has been an FLL coach since 2002. He is a member of the 2009 FLL Smart Move challenge design team.

Axis 206 Camera Green Lamp Imaging

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The Axis 206 Network Camera can be used to image the green cold-cathode lamp used in the 2006 and 2007 FRC games, but the default camera settings do not work well for that application. To complicate matters, the camera interface does not provide a method to directly set the camera to work well with the FRC green lamp. This article explains why the default settings do not work well and how to indirectly change the settings for excellent green lamp imaging.

Overview

The author used two software tools in working with the Axis 206 camera. The Axis 206 Camera Web Server interface was used to change camera settings and to capture images. The National Instruments Vision Assistant was used to process the captured images.

Phil Malone (Mentor: Team 1629) has further developed the procedure by adapting the LabVIEW FRC “Locate Colored Object” example, and he describes his easy-to-use method in another Think Tank article.

Once the FRC green lamp has been turned on for a period of time, its light level and color properties stay relatively constant, even under differing lighting conditions. It is these constant properties of the green lamp – it’s hue, saturation and luminance – that can be used in identifying and locating the lamp.

By default, the Axis 206 exposure and white balance are set to automatically adjust to compensate for differing lighting conditions. Automatic adjustment may work well when capturing images of reflected light of variable level and color temperature. However, it is better to use fixed exposure level and white balance settings to capture an image of a light source whose brightness and color temperature remains relatively constant under variable lighting conditions.

If the camera is allowed to automatically vary exposure and white balance when imaging the green lamp under variable lighting conditions, the apparent properties of the lamp will vary from image to image as the camera auto-adjusts to the lighting conditions. In order to obtain consistent imaging of the lamp, the exposure and white balance settings can be fixed at the optimum “green-lamp” level. Achieving that optimum level is the trick.

When auto-adjusting for exposure, the Axis camera seems to adjust for average brightness of the image. If the green lamp fills the entire image, auto-adjustment will achieve the correct exposure for the lamp. The camera exposure can then be held fixed. The camera will retain its settings even if powered off and then on again.
 

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