Caltech light-cancelling camera reduces glare by factor of ten
A research team at the the California Institute of Technology (Caltech) in the USA is developing a cost-effective noise cancelling camera that counteracts glare in an image.
The research was presented in Optica in October and demonstrated an ability to reduce the effects of the unwanted light by a factor of 10.
The camera cancels out unwanted light by using illumination that matches the coherence of the glare. The camera shows promise in applications such as microscopy, where scientists experience noise from light when looking through skin or other membranes, or astronomy, where images of planets can be obscured by the light from bright stars.
‘We are trying to invent a type of noise-cancelling camera by separating the glare from the target’s reflection so that the target can easily be seen,’ said Edward Haojiang Zhou, a graduate student at Caltech and first author of the Optica paper.
Zhou and the researchers showed that their approach can reduce glare by a factor of 10, and were able to produce images of an object placed 2mm behind a 1mm-thick, light-scattering sample.
‘By changing the coherence of the light, the method we demonstrated can be used to simultaneously image objects at various distances from the light source,’ said Zhou. ‘This provides a great deal of freedom for imaging through scattering samples with thicknesses from 1mm to a kilometre.’
In contrast to other approaches used to compensate for glare, which require expensive and complicated equipment, the Caltech setup uses basic and readily available optical components. The researchers are now working to apply their technique to improve the quality of images taken by satellites and plan to try it with astronomy applications, where it could help researchers peer through the opaque atmospheres of other planets, such as Venus.
An alternate approach to reducing the effects of glare was recenelty demonstrated at the Weizmann Institute of Science in Israel, where instead of changing the light’s coherence as with Caltech’s camera, glare was reduced by using wavefront shaping to change the field of the light illuminating the object. This method minimises the amount of blinding light scattered into the camera by using an optical device called a spatial light modulator (SLM) and an optimisation algorithm to control the shape of the impinging light field.
As in Caltech‘s work, wavefront shaping operates by the light from the object and the background being mutually incoherent to cancel out the glare. The unwanted light must also be fairly static for the optimisation process to be effective.
‘Our lab uses wavefront shaping for many different purposes,’ said Professor Yaron Silberberg, head of the research team in Israel. ‘We are trying to develop a toolbox where, using wavefront shaping and SLMs, you can improve imaging, especially under difficult conditions. Glare reduction will be part of this toolbox.’ Silberberg’s paper was also published in October’s Optica.