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Firmware makes fluorescent-lit videos flicker-free

Posted: 26 Jun 2008 ?? ?Print Version ?Bookmark and Share

Keywords:flickering video? surveillance camera firmware? CCD sensors?

Pixim Inc. announced that it has solved a persistent technical issue affecting the accuracy and usability of CCD video security cameras worldwide.

With its V3.2 firmware with Enhanced Flicker Reduction (EFR) mode, Pixim overcomes video sampling issues that can diminish camera performance, including fluorescent light flicker, fluorescent color roll and frequency-modulated LED "blackout." These issues all are caused by differences between the video field capture frequency (which is set by global standards bodies) and the local AC power frequency (which varies by geographic location).

"As incandescent lighting continues to be eliminated due to energy efficiency concerns, fluorescent and LED light sources will become increasingly widespreadas will the serious video capture issues associated with them," said Mark Kirstein, president of market research consultancy Multimedia Intelligence. "Pixim's EFR technology is the industry's first real solution for fluorescent- and LED-related video capture problems that also maintains wide dynamic range and true color."

"These video sampling issues range from an annoyance to a serious security hindrance," said John Monti, VP of marketing and business development. "Pixim has devised the first solution that overcomes these industry-wide issues among CCD video cameras while also retaining wide dynamic range capabilities, meaning true natural color and accurate image capture under variable lighting conditions."

The Pixim EFR mode works with video cameras powered by Pixim Digital Pixel System technology.

Solving CCD video issues
The three issues addressed by Pixim's EFR mode are fluorescent color roll, frequency-modulated LED blackout and fluorescent light flicker. They result from differences between the video field capture frequency and local AC power frequencies.

Fluorescent color roll happens because the spectral characteristics of fluorescent lights change within each AC power cycle, as the illumination level changes. It is a worldwide problem, affecting North and Central America, western Japan, other Asian countries and most of South America, the Caribbean and the Pacific.

NTSC video frequencies are 59.94Hz, a slight difference from the 60Hz AC power frequency that is used in most NTSC areas. In this situation, the camera's image captures will sweep through the entire illumination cycle of the fluorescent light every 8s, and the color of the fluorescent light will appear to change in the captured video. This effect is referred to as "color roll."

Using a Pixim-powered camera with V3.2 firmware and EFR mode is the only way to solve this problem and to capture colors accurately under fluorescent lights while preserving 15bits of dynamic range.

Frequency-modulated LED blackout, affecting the same geographic regions as fluorescent color roll, occurs with low-powered solid-state lights, such as the LEDs used in traffic and signal lights, vehicle headlights and flashlights. These LEDs are not continuously powered, but rather their power is modulated to save energy and extend the life of the LED. At the same time, however, this power modulation causes the lights to "blink," which creates problems for video cameras.

LEDs "blink" at 120Hz frequency, creating an LED time base mismatch in areas that use the NTSC field rate of 59.94Hz along with 60Hz AC power. In captured video, the LEDs will appear to go dark for a period of time every 8s. As a result, security cameras cannot accurately capture LED-based traffic and train signals. This is a problem because it is important to be able to accurately capture the illumination state of these signals for forensics purposes (i.e., to tell whether a traffic light was showing green, yellow or red at the moment of a traffic collision).

Fluorescent light flicker occurs because fluorescent light output is not constant, and in fact flickers. Video captured under fluorescent lighting includes a constant beating, strobe-light effect that makes the video difficult to watch. As a result, people are physically unable to monitor the flickering video for any length of time, which can lead to unmonitored security cameras.

Fluorescent light flicker becomes an issue in places where AC voltage cycles at 50Hz and the TV standard is NTSC (59.94Hz)primarily in eastern Japan, Chile and some other Latin American, Caribbean and Pacific nations. The flicker problem cannot be solved for standard CCD sensors. Only Pixim-powered cameras with the new V3.2 firmware with EFR can overcome the fluorescent light flicker while maintaining a full 15bits of dynamic range.

The Pixim V3.2 firmware for Orca chipsets began shipping to camera companies in May, and the first Pixim-powered cameras with EFR are expected to reach the market in Q3 08. The EFR capability will be a standard feature with all future versions of Pixim's Orca firmware. A 32Mbit flash is required to support the EFR mode.

- Video Imaging DesignLine





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