Video data reduction allows energy-saving data glasses
Offering the benefit of hands-free operation, data glasses are ideal for Augmented Reality applications where, for instance, they mirror relevant information to the operator’s eye regarding the assembly procedure he is currently busy with. Thus, the operator can view assembly plans while they are working. Likewise, data googles are becoming attractive for cyclists: they can display navigation hints without the urging the driver to take his hands off the handlebars; the smartphone can stay in the backpack.
The high power consumption of data glasses nevertheless has prevented that they have become a market success. Since processing video data is still a rather energy-consuming task, the batteries of data glasses typically do not last longer than an hour or so before they need to be recharged.
Researchers from the Fraunhofer institute for Organic Electronics, Electron Beam and Plasma Technology (EFP) in Dresden now have succeeded in developing a display that combines the benefits of offering a particularly bright screen and low power consumption. Today, organic LEDs (OLEDs) are combined with a silicon pixel driver on a single chip. In addition, the Fraunhofer experts integrated a complete camera function on that chip. Thus, the OLED micro displays can be used not only to display an image but also to perceive its surroundings. Towards this end, a light-sensitive photodiode has been added to each pixel. The camera function is relevant for future VR and AR usage: It enables the software to sense the direction where the wearer looks and thus provide the appropriate information on the display.
This feature however does not yet resolve the power consumption problem. The Fraunhofer researchers attacked this issue with a completely new approach that reduces the amount of video data to be processed: Traditionally, video displays for real-time applications like data glasses process 60 frames per second which leads to high data throughput and thus to high power consumption. The Fraunhofer team around Philipp Wartenberg had the idea of reducing the data stream to the necessary amount. Only those data that are altered at any given moment are renewed on the display. If, for instance, a person runs through the image, only the pixels representing this person are changing; the background pixels remain the same and therefore do not need to be processed and transferred. To reduce the video data stream, the team had to redesign the video processor and the related circuitry from scratch. Today’s pixels, designed for fast refresh rates, typically stop emitting light after a short time. In a design that does not require the entire screen to be refreshed constantly, another approach to drive the OLED pixels is necessary, because otherwise the unaltered areas of the screen would then appear black. “Simply put, we have modified the circuitry so that it passes on only those parts of the data stream that has changed since the past frame,” Wartenberg explained.
This feature drastically reduced the power required, Wartenberg said. The team presented a prototype that suffice with just two to three milliwatts. For comparison: Conventional data googles consume some 200 milliwatts.
The prototype will be exhibited at the electronica next week; Fraunhofer FEP is in hall A4, booth 113.
Read also:
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OLED microdisplays double as eye trackers
Sony transforms eyewear into smart augmented reality devices
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