A bright flash in the dark may now be a thing of the past. (Image: James Curley/Rex Features) Infrared and ultraviolet light is used to take the initial image, but the hues look unnatural. So accurate colours are added via a second brief exposure taken with ambient light (Image: Dilip Krishnan and Rob Fergus)

A camera that takes photos with an invisible flash of infrared and ultraviolet light points to a smarter way to take photos in the dark.


Dilip Krishnan and Rob Fergus at New York University created the camera in an attempt to do away with intrusive regular flashes.

To make their “dark flash” camera, they modified a flashbulb to emit light over a wider range of frequencies and filter out visible light. The pair also had to remove the filters that usually prevent a camera’s silicon image sensor detecting IR and UV rays.

See an image gallery explaining the dark flash system

Twin exposures

Although the dark flash gives a crisp image without disturbing those in the picture, the results have an odd colour balance that looks like a view through a night-vision scope.

To give the pictures more normal hues, Krishnan and Fergus used colour information from a brief, flash-free photograph of the same scene taken quickly after the dark flash image.

The second image is dim and blurry, and so it lacks some of the fine detail of its dark flash twin. However, the researchers use software to combine the sharp detail from the first image with the natural colours from the second image, resulting in a remarkably natural end result.

See an image gallery demonstrating the dark flash system

Blind spots

Despite the impressive results, a few problems remain. Some materials or objects absorb both UV and IR light and so don’t appear in the dark flash image or the reconstruction. For instance, the subject’s freckles are visible in the long-exposure image, but not in the computer-reconstructed image.

Amit Agrawal at Mitsubishi Electric Research Labs in Cambridge, Massachusetts, says that computer scientists have already found many uses for this type of flash/ambient light twin photography.

In 2005 his team showed thatcombining ambient and flashlight images can remove unwanted reflections from images, and more advanced tricks using the technique include making instant 3D models.

Krishnan and Fergus will present their work at the Siggraph conference in New Orleans in August.