Monday, January 09, 2012

#OPTICS: "Smarter Cameras Focus After Shooting"

Light-field cameras capture images in all possible focal planes simultaneously, allowing users to refocus them after they have been taken, albeit at the cost of lower resolution.

Images captured by light field cameras can be focused after shooting, here on the background (left) or foreground (right). (Source: Lytro)

Light-field cameras capture not only light, but also the direction it came from. This permits the user to take the photo first and focus it later. The photographer can also create 3D images from that single shot, using after-the-fact software conversions, which deduce perspective from the distance to objects in a scene.

Conventional cameras require that photographers set the focus before shooting, in effect narrowing down the direction from which light rays can impinge on the sensor, resulting in a single plane that is clear. By adjusting the focus ring on a conventional camera, that focal plane can be adjusted from its closest setting all the way out to the horizon. Depending on the depth-of-field for a particular aperture setting, that focal plane can be adjusted to include a wide or narrow swath.

A light-field camera, on the other hand, inserts an array of micro-lenses in front of the image sensor, in effect recording the images in all focal planes simultaneously. And because software can deduce which parts of an image are in focus, software can, after the fact, create the perspective needed to generate 3D images using a single camera.

The first commercial light-field camera comes from Raytrix GmbH. The camera uses about 40,000 micro-lenses to capture images of from 1 to 3 megapixels of resolution depending on the model chosen. Raytrix will also take your existing digital camera and convert it to a light-field camera by building a custom micro-lens array for it. The company's proprietary software then allows users to adjust the focus, or create 3D images, after shooting.

Raytrix’s cameras are often customized for a specific application, resulting in price tags of over $10,000, which is reasonable for industrial applications, such as for inspection, and even for high-end security systems where personnel can adjust the focus after shooting to clear up who or what transpired when no one was looking.

Next year a new company, Lytro, will be delivering a consumer version of a light-field camera for under $500. The Lytro camera has an 11-megapixel image chip from which software generates square HD images of 1,080 by 1,080 pixels, focused in any plane. The focus-free shooting will be a boon to applications that are stunted today by shutter lag while waiting for auto-focus mechanisms to kick in--such as candid photography. The Lytro light-field camera, on the other hand, has zero shutter lag for an 8X zoom lens at f2.0--fast enough even for sports photography.