System brightens dark video

As anyone who has used a video camera knows, the picture is sometimes murkier than real life.

Researchers from the University of North Carolina at Chapel Hill have devised a way to improve under-exposed videos.

The method sharpens and brightens videos that are too dark or that have only a single object fully exposed. It works with any kind of video from home videos to professional footage, according to the researchers.

The method could also eventually be built into camcorders to make it easier to capture darkly-lit scenes. It could also eventually be used to improve night vision systems.

The trick to improving dark footage is avoiding accentuating the stray dark pixels, or noise, commonly found in dark videos.

Some noise-reduction techniques attempt to improve quality within a single frame. Other techniques attempt to remove noise by analyzing a single pixel over the course of a few frames. The researchers' method uses both techniques, starting with the multiframe method and switching to the single frame filter for pixels that move from frame to frame.

The system is based on the notion of a virtual exposure camera that can simulate longer exposure times for darker image regions. The result is a video that appears to have been captured under balanced, consistent lighting conditions.

The researchers' method reduces noise and enhances contrast consistently between frames so that the frames don't flicker when played back at full speed.

The researchers are scheduled to present the work at the Special Interest Group Graphics (Siggraph) 2005 conference on August 3 in Los Angeles (Video Enhancement Using Per-Pixel Virtual Exposures).