Asynchronous Stroboscopic Structured Lighting Image Processing Using Low-Cost Cameras

Abstract

Structured lighting (SL) image processing relies on the generation of known illumination patterns synchronized with the camera frame rate and is commonly implemented using syncing capable cameras. In general, such cameras employ global shutters, that exposes the whole frame at once. However, most modern digital cameras use rolling shutters, which expose each line at different intervals, impairing most structured lighting applications. In this paper we introduce an asynchronous SL technique that can be used by any rolling shutter digital camera. While the use of stroboscopic illumination partially solves for the line exposure shift, the phase difference between the camera and lighting clocks results in stripe artifacts that move vertically in the video stream. These stripes are detected and tracked using a Kalman filter. Two asynchronous stroboscopic SL methods are proposed. The first method, image differencing, minimizes the stripe artifacts. The second method, image compositing, completely removes the artifacts. We demonstrate the use of the asynchronous differential lighting technique in a pupil detector using a low-cost high-speed camera with no synchronization means, with the lighting running independently at a higher, unknown frequency to the application.