© Fraunhofer IOSB

Light field technology

The classic PC screen on our desk can only display 2D image content, which looks identical from every viewing direction. A light field display, on the other hand, can simultaneously project different information in different directions. Imagine a display in the center console of the car that shows the driver the navigation while the front passenger can watch a movie at the same time. We go even further and project different image content in up to 1,600 different directions at the same time.

Functional principle

A light field emitter is a planar light source in which both the position and the direction of light emission can be controlled. Our prototype combines a monitor with an array of lenses mounted in front of it at the distance of the focal lengths of the individual lenses. If a pixel is activated behind an individual lens, the light field display emits a parallel bundle of rays whose direction of propagation is defined by the spatial position of the activated pixel behind the individual lens. In this way a 4D light field is projected into space. Its spatial resolution corresponds to the number of individual lenses in the lens array; the angular resolution is determined by the number of monitor pixels behind each individual lens.

© Fraunhofer IOSB
Figure 1: Construction of a light field display. Our prototype combines a monitor with a lens array, which is located in front of the monitor at a distance equal to the focal length of the individual lenses. If a pixel behind one of the lenses is activated, the light field display emits a parallel beam of light whose direction of propagation is defined by the spatial position of the activated pixel behind the individual lens. In this way, the light field is projected into the room.

Application in optical inspection

These additional control variables (in addition to pixel rows and columns also horizontal and vertical direction of emission) open up additional possibilities: Such a light field display can be used for visual inspection in order to illuminate objects with complex geometries with a specially adapted "light recipe" in such a way that relevant structures can be captured with maximum contrast.

© Fraunhofer IOSB
Figure 2: Use of a light field display for problem-specific illumination in industrial visual inspection. Test specimen: Glass plate with defect at the edge top right. Left: Classic bright field illumination - the defect is barely visible. Right: Light field illumination (colour-coded) - the defect is very clearly visible with strong contrast.

In order to demonstrate the variety of adjustable lighting modalities, we show below the use of our prototype as an autostereoscopic display. For this purpose we synthetically generated 361 views of a Rubik's Cube and rendered them into a 2D representation that is displayed on the screen of the light field display. The lens array then projects this into the room as a 4D light field, which we again recorded with a camera from nine different viewing angles. As can be seen, the emitted light field is very similar to the original light field data.

© Fraunhofer IOSB
Figure 3:
Left: synthetically generated views of a Rubik's Cube.
Center: rendered 2D representation oft he 4D light field data, as shown on the light field display’s monitor
Right: projected light field, recorded from 9 different perspectives
 

Department SPR of Fraunhofer IOSB

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Further projects of the SPR department

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