Minimizing latency for augmented reality displays: Frames considered harmful

We present initial results from a new image generation approach for low-latency displays such as those needed in head-worn AR devices. Avoiding the usual video interfaces, such as HDMI, we favor direct control of the internal display technology. We illustrate our new approach with a bench-top optical see-through AR proof-of-concept prototype that uses a Digital Light Processing (DLPTM) projector whose Digital Micromirror Device (DMD) imaging chip is directly controlled by a computer, similar to the way random access memory is controlled. We show that a perceptually-continuous-tone dynamic gray-scale image can be efficiently composed from a very rapid succession of binary (partial) images, each calculated from the continuous-tone image generated with the most recent tracking data. As the DMD projects only a binary image at any moment, it cannot instantly display this latest continuous-tone image, and conventional decomposition of a continuous-tone image into binary time-division-multiplexed values would induce just the latency we seek to avoid. Instead, our approach maintains an estimate of the image the user currently perceives, and at every opportunity allowed by the control circuitry, sets each binary DMD pixel to the value that will reduce the difference between that user-perceived image and the newly generated image from the latest tracking data. The resulting displayed binary image is “neither here nor there,” but always approaches the moving target that is the constantly changing desired image, even when that image changes every 50μs. We compare our experimental results with imagery from a conventional DLP projector with similar internal speed, and demonstrate that AR overlays on a moving object are more effective with this kind of low-latency display device than with displays of similar speed that use a conventional video interface.