Dazzlingly sharp images on curved screens

October 27, 2014, Fraunhofer-Gesellschaft
Micro-optical array projectors: Double-sided lens array with buried slide array (left) and lens array with buried color filters for LCD micro-imager (right). Credit: Fraunhofer IOF

Projecting images on curved screens poses a dilemma. The sharper the image, the darker it is. A novel optical approach brings brightness and sharpness together for the first time on screens of any curvature – and additionally allows about 10,000-times faster projection rates. Researchers will be presenting their technology November 4-6 at Vision 2014 in Stuttgart. (Hall 1, Booth G42)

The logo glows above the overhang of the wall and ledge of the large office building, immediately identifying the enterprise hidden behind the façade to passersby. Made possible by a projector throwing up a suitable slide onto the wall. However, what works well on flat projection surfaces is fraught with difficulties for curved or uneven surfaces like a façade, however. To achieve sufficient sharpness and depth of field, the aperture must be closed down. But the smaller this opening, the less brightness is achieved – just like with cameras. There is a way around this problem using a laser. Scanning mirrors can direct the laser light so the desired image is created. This process has its drawbacks, however. The setup is complicated and expensive.

Sharpness and brightness at the same time

Researchers from the Fraunhofer Institute for Applied Optics and Precision Engineering IOF in Jena, Germany, have applied a proven approach used with cameras. "We close the aperture down to 0.8 mm and thereby attain huge depth of field," IOF scientist Dr. Peter Schreiber divulges. But in contrast to solutions used up to now, the image projected by IOF is bright. "We create the desired brightness by placing several microprojectors beside one another – known as an array." To make a long story short, the light from the individual devices is additive – if the image is supposed to brighter, you simply increase the number of projection elements.

The projector can be up to ten by ten centimeters in size for instance, while its thickness is about a centimeter – independent of the number of projectors. "While the exit aperture in today's projectors is round, we can construct whatever aperture shape we want," says Schreiber. That means the projector can cast bright and sharp images on a screen of any curvature while possessing its own shape – a logo, for instance – that itself resembles an image. The projector in the shape of a company logo could be mounted on a reception area wall, for example, while at the same time projecting an image on the opposite wall.

Assembled like pieces of a mosaic

If you look more closely at the projector, you see that it consists of numerous 1 cm x 1 cm elements resembling a mosaic. And within each of these elements in turn, there is a single LED and more than a hundred micro-projectors – i.e. a self-contained micro-slide with micro-illumination and micro-projection lenses. However, the researchers do not manufacture these micro-projectors individually, but instead as arrays. They overlay the slide array with the lens arrays. "We can use this building block to work with different screen geometries and projection distances," explains Schreiber. In addition, the optical array has a further advantage: if the geometry of the projection surface or the projection distance change, it is no longer necessary to reconfigure the entire optical system as before, but instead only just the slide array. The optical array itself remains unchanged.

Rapid projection rates

While high-speed cameras can take up to ten-thousand images per second, conventional projectors are slow. They can only reproduce about one-hundred images per second. This difference can lead to problems, since a rate of a hundred images per second is often insufficient. Like when projecting stripes used for measuring moving surfaces. "Our array can project a million images per second," Schreiber was pleased to offer. That is about 10,000 times faster than conventional projectors. The array can also project dynamic images. Instead of using a slide array, the researchers build in a micro-imager behind the individual lens.

Explore further: Mini-projector for smartphones

Related Stories

Mini-projector for smartphones

May 10, 2012

Their very small displays sometimes make smartphones diffi cult to operate. In the future, a projector will help: if the cell phone is standing on a table, for instance, it can project a large-format display onto the table ...

Mini-projectors -- maximum performance

May 20, 2010

(PhysOrg.com) -- The number of mini-projector devotees keeps growing. The combination of a new kind of optical structure with high-performance LEDs enables completely new compact and brilliant lighting and projection systems.

Warping images using your PC graphics card

January 2, 2014

By projecting images onto contoured surfaces you get a virtual experience that puts you at the center of the action. Now, a quick and easy calibration technique could help the concept find a wider application beyond the planetarium.

Osram LEDs for Mini Projectors

March 4, 2010

New, particularly high-performance light-emitting diodes (LEDs) from Osram make it possible to build mini projectors. These LEDs produce enough light to project images measuring over one meter in diagonal on a wall. The small, ...

Recommended for you

Two new planets discovered using artificial intelligence

March 26, 2019

Astronomers at The University of Texas at Austin, in partnership with Google, have used artificial intelligence (AI) to uncover two more hidden planets in the Kepler space telescope archive. The technique shows promise for ...

Infertility's roots in DNA packaging

March 26, 2019

Pathological infertility is a condition affecting roughly 7 percent of human males, and among those afflicted, 10 to 15 percent are thought to have a genetic cause. However, pinpointing the precise genes responsible for the ...

Facebook is free, but should it count toward GDP anyway?

March 26, 2019

For several decades, gross domestic product (GDP), a sum of the value of purchased goods, has been a ubiquitous yardstick of economic activity. More recently, some observers have suggested that GDP falls short because it ...

Droughts could hit aging power plants hard

March 26, 2019

Older power plants with once-through cooling systems generate about a third of all U.S. electricity, but their future generating capacity will be undercut by droughts and rising water temperatures linked to climate change. ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.