Engineers at Rice University have unveiled a new type of 3D camera system, dubbed a Hyperspectral Stripe Projector (HSP), which combines four dimensions: the three spatial dimensions, plus a spectral dimension.
"We’re getting four-dimensional information from an image, three spatial and one spectral, in real time," Associate Professor Kevin Kelly explains of the team's work. "Other people use multiple modulators and thus require bright light sources to accomplish this, but we found we could do it with a light source of normal brightness and some clever optics."
"Regular RGB (red, green, blue) cameras basically give you only three spectral channels," adds lead author Yibo Xu. "But a hyperspectral camera gives us spectra in many, many channels. We can capture red at around 700 nanometers and blue at around 400 nanometers, but we can also have bandwidths at every few nanometers or less between. That gives us fine spectral resolution and a fuller understanding of the scene."
"HSP simultaneously encodes the depth and hyperspectral measurements in a very simple and efficient way, allowing the use of a monochrome camera instead of an expensive hyperspectral camera as typically used in similar systems."
The core concept is the same as used in existing consumer 3D imaging systems, like those used for facial recognition in smartphones, but concentrates on pulling spectral data for each pixel — capturing, the researchers claim, not only the shape of an object but also its material composition.
The camera system is based on existing hardware: "We use a single DMD [digital micromirror device] and a single [diffraction] grating in HSP," Xu explains. "The novel optical design of folding the light path back to the same diffraction grating and lens is what makes it really compact. The single DMD allows us to keep the light we want and throw away the rest."
The team's work has been published under open-access terms in the journal Optics Express.