Temporal Dithering of Illumination for Fast Active Vision

Abstract

Abstract. Active vision techniques use programmable light sources, such as projectors, whose intensities can be controlled over space and time. We present a broad framework for fast active vision using Digital Light Processing (DLP) projectors. The digital micromirror array (DMD) in a DLP projector is capable of switching mirrors "on" and "off" at high speeds (10 6 /s). An off-the-shelf DLP projector, however, effectively operates at much lower rates (30-60Hz) by emitting smaller intensities that are integrated over time by a sensor (eye or camera) to produce the desired brightness value. Our key idea is to exploit this "temporal dithering" of illumination, as observed by a high-speed camera. The dithering encodes each brightness value uniquely and may be used in conjunction with virtually any active vision technique. We apply our approach to five well-known problems: (a) structured light-based range finding, (b) photometric stereo, (c) illumination de-multiplexing, (d) high frequency preserving motion-blur and (e) separation of direct and global scene components, achieving significant speedups in performance. In all our methods, the projector receives a single image as input whereas the camera acquires a sequence of frames.

Selection of temporally dithered codes for increasing virtual depth of field in structured light systems

“…In general, structured light systems have been developed around off-the-shelf digital projectors with limited modifications [2,3,4,5,6]. Since these projectors are not designed for structured light applications, some of their inherent qualities become problematic for depth capture.…”

“…Since most DLP projectors are only capable of projecting patterns at a rate of 60 frames per second (fps), it is difficult to use these projectors to capture fast moving dynamic scenes. Temporally dithered codes have recently been shown to significantly increase the rate at which codes are projected from a standard DLP projector [2]. These codes make it possible to capture dynamic scenes with faster motion than has been possible with traditional 60 fps projection.…”

Ultrafast 3-D shape measurement with an off-the-shelf DLP projector

“…Davis et al has developed a realtime 3-D shape measurement system based on Spacetime stereo vision method [12]. Recently, Narasimhan et al developed a temporal dithering technique for 3-D shape measurement [13]. However, unlike an aforementioned sinusoidal fringe analysis technique, it is difficult for any of binary structured pattern based methods to reach pixel-level spatial resolution because the stripe width must be larger than one projector pixel [14].…”

Motion deblurring with temporally coded illumination in an LED array microscope

“…By "fluttering" the camera's shutter open and closed during the chosen exposure time, the resulting filter can be broadband, and the deblur problem becomes wellposed [8,9]. This coded exposure method has been recently adapted to flash imaging [10], fluorescence microscopy [11], and illumination coding [12]. Here, we apply the same strategy for illumination coding in our LED array microscope, whose LEDs are already capable of modulation at speeds much faster than the camera exposure time.…”