Vision-correcting displays Researchers at the MIT Media Laboratory and the University of California at Berkeley have developed a new display technology that automatically corrects for vision defects   no glasses (or contact lenses) required. The technique could lead to dashboard-mounted GPS displays that farsighted drivers can consult without putting their glasses on or electronic readers that eliminate the need for reading glasses among other applications. The first spectacles were invented in the 13th century  says Gordon Wetzstein a research scientist at the Media Lab and one of the display's co-creators.  Today of course we have contact lenses and surgery but it's all invasive in the sense that you either have to put something in your eye wear something on your head or undergo surgery. We have a different solution that basically puts the glasses on the display rather than on your head. It will not be able to help you see the rest of the world more sharply but today we spend a huge portion of our time interacting with the digital world. Wetzstein and his colleagues describe their display in a paper they're presenting in August at Siggraph the premier graphics conference. Joining him on the paper are Ramesh Raskar the NEC Career Development Professor of Media Arts and Sciences and director of the Media Lab s Camera Culture group and Berkeley s Fu-Chung Huang and Brian Barsky.Knowing the angles. The display is a variation on a glasses-free 3-D technology also developed by the Camera Culture group. But where the 3-D display projects slightly different images to the viewer's left and right eyes the vision-correcting display projects slightly different images to different parts of the viewer's pupil. A vision defect is a mismatch between the eye's focal distance   the range at which it can actually bring objects into focus   and the distance of the object it s trying to focus on. Essentially the new display simulates an image at the correct focal distance somewhere between the display and the viewer's eye. The difficulty with this approach is that simulating a single pixel in the virtual image requires multiple pixels of the physical display. The angle at which light should seem to arrive from the simulated image is sharper than the angle at which light would arrive from the same image displayed on the screen. So the physical pixels projecting light to the right side of the pupil have to be offset to the left and the pixels projecting light to the left side of the pupil have to be offset to the right.The use of multiple on-screen pixels to simulate a single virtual pixel would drastically reduce the image resolution. But this problem turns out to be very similar to a problem that Wetzstein Raskar and colleagues solved in their 3-D displays which also had to project different images at different angles.The researchers discovered that there is in fact a great deal of redundancy between the images required to simulate different viewing angles. The algorithm that computes the image to be displayed onscreen can exploit that redundancy allowing individual screen pixels to participate simultaneously in the projection of different viewing angles. The MIT and Berkeley researchers were able to adapt that algorithm to the problem of vision correction so the new display incurs only a modest loss in resolution.In the researchers  prototype however display pixels do have to be masked from the parts of the pupil for which they re not intended. That requires that a transparency patterned with an array of pinholes be laid over the screen blocking more than half the light it emits. Multitasking But early versions of the 3-D display faced the same problem and the MIT researchers solved it by instead using two liquid-crystal displays (LCDs) in parallel. Carefully tailoring the images displayed on the LCDs to each other allows the system to mask perspectives while letting much more light pass through. Wetzstein envisions that commercial versions of a vision-correcting screen would use the same technique.Indeed he says the same screens could both display 3-D content and correct for vision defects all glasses-free. They could also reproduce another Camera Culture project which diagnoses vision defects. So the same device could in effect determine the user s prescription and automatically correct for it. Most people in mainstream optics would have said Oh this is impossible, says Chris Dainty a professor at the University College London Institute of Ophthalmology and Moorfields Eye Hospital.  But Ramesh's group has the art of making the apparently impossible possible. MIT researchers explain how their vision-correcting display technology works. The key thing is they seem to have cracked the contrast problem  Dainty adds.  In image-processing schemes with incoherent light  normal light that we have around us nonlaser light  you're always dealing with intensities. And intensity is always positive (or zero). Because of that you're always adding positive things so the background just gets bigger and bigger and bigger. And the signal-to-background which is contrast therefore gets smaller as you do more processing. It's a fundamental problem. Dainty believes that the most intriguing application of the technology is in dashboard displays.  Most people over 50 55 quite probably see in the distance fine but can't read a book,  Dainty says.  In the car you can wear varifocals but varifocals distort the geometry of the outside world so if you don't wear them all the time you have a bit of a problem. There [the MIT and Berkeley researchers] have a great solution.