Reducing fluorescent flicker in security camera video

The technical problem with video cameras and fluorescent lighting takes shape in slightly different ways worldwide, but it boils down to a video sampling issue that occurs when there's a difference between the video field capture frequency (which is set by global standards bodies) and local AC power frequency (which varies by geographic location).

This mismatch results in everything from video images whose color shifts every few seconds to video that "beats" so strongly that operators are physically unable to watch it continuously. A closely related technical issue also affects scenes with LED lighting sources, causing the video images to go dark every few seconds.

Some of the results are simply annoyances, but at other times they can seriously hinder effective security.

These video sampling issues are not readily apparent to people looking directly at a scene lit by fluorescent lights or LEDs, thanks to a natural effect known as "eye persistence." Unlike video cameras, when humans view a scene our brains "fill in the gaps" between fast-flickering lights. The human eye perceives the lighting as constant -- in the same way we perceive the fast-moving frames of projected movies as continuous motion.

Through the years, a number of approaches have been tried to solve the video sampling issues caused by fluorescent and LED frequencies and their mismatch with AC power frequencies. These other approaches, however, significantly reduce the dynamic range of the video camera for fluorescent-lit scenes. This loss of information is not an acceptable trade-off for many video security applications.

Pixim Inc. has recently solved the persistent technical issues of fluorescent light flicker, fluorescent color roll and frequency-modulated LED "blackout" -- while also retaining ultra-wide dynamic range capabilities, for true natural color and accurate image capture even under variable lighting conditions. Pixim's Enhanced Flicker Reduction (EFR) mode represents the first real solution to this persistent technical issue.

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