Lytro’s Awesome Plenoptic Camera Lens
It’s impossible to look at Lytro’s plenoptic consumer cameras and not see potential for use in video surveillance applications.
FOR CCTV people the best way to guarantee focus in a large, deep scene is super high resolution. This allows digital zoom to be employed to dig into scenes later on. The cost is very large file sizes and there’s an inevitable trade off in storage space and bandwidth that often lead to applications that reek of compromise.
Solutions that mirror a plenoptic function include Dallmeier’s Panomera, which uses multiple 2MP CCTV cameras each with a different focal length in an array that’s directed at a single scene. Depending on the depth of field you want in focus, the system selects different images from different cameras – it’s a brilliant solution.
What if there was more compact and less expensive solution of low end cameras? If Lytro is anything to go by, the technology certainly exists to do things differently. Lytro Light Field is a plentoptic camera that uses an array of hundreds of micro-lenses to gather a 4D light field – all the light rays reflected from a scene – which allows the camera’s software engine more data to chew on. The result is an image that can be refocused after it’s taken.
With a Lytro camera, a scene can be focused to the front to show a face and then focused to the rear to offer situational awareness all from the same image. While the final image resolution is kept relatively low at 1.1MP – 1080p x 1080p – the overall image size is relatively large at 11MP but that’s small relatively considering the potential of the technology to offer face recognition or LPR in all parts and depths of a scene.
Plenoptic technology is actually around 100 years old – it was developed by Gabriel Lippmann in 1908 and enhanced by Adelson and Wang who in 1992, slashed correspondence in stereo matching by placing the microlens array at the focal plane of the main camera lens – at the front of the camera with the image sensor just aft.
There are negatives of the system relating to low resolution – an image has the resolution of the microlens that is in focus in a given part of the scene. A focused plenoptic camera can resolve these issues, however, giving more spatial resolution and less angular resolution. Focus can also be a little slow – but it’s early days yet.
Obviously, the beauty of this technology is that would allow camera manufacturers, integrators and end users to side step the fundamental truth that an image’s best focal point is set at the point of exposure. The ability to go through the scene from front to back afterwards is extremely cool and in many video surveillance applications it would be profoundly useful.
Quite simply, as you shift the focal point on a Lytro camera, the image refocuses with complete clarity. Reviewers of Lytro have pointed out that the camera image quality is not up with the best. High contrast edges suffer from chromatic aberration and that most important of features, wide dynamic range, is comparatively low. Importantly though, images contain only small amounts of noise.
Lytro cameras are supported by Lytro management software and this includes something rather neat called Perspective Shift. It’s a function that allows an operator to move around and into a scene, moving seamlessly around a fully focused image, which gives its operators the sense of moving around a 3D object – it’s gaming stuff in real life.
Obviously, Lytro is proprietary and targeted at consumers but it’s technologies like this that give us hints of where clever CCTV camera manufacturers might go in the future. Something interesting is price. The camera, which also has Wi-Fi connectivity for download and sharing, is about $US400, which is not much to ask for technology as clever as this is.