All-digital phase code: a proposal for high-speed 3D-shape recording

摘要

The use of computer generated sinusoidal fringe patterns has found wide acceptance in optical metrology. There are corresponding software solutions that reconstruct the phase field coded in the fringe pattern in order to get 3D-shape data via triangulation and deflection measuring setups, respectively. Short recording time is a common issue of high importance for all tasks on the factory shop floor as well as in applications for life sciences and for security locks. Recent high-speed implementations take advantage of MEMS based spatial light modulators and the digital micromirror chipset DMD Discovery~(TM) is the fastest mature component currently available for this ami. Being an on-off-state system, the sinusoidal gray level pictures recorded by a tune averaging analog detector are produced using the DMD pulse-width modulation (PWM). This digital generation of "intensities" provides outstanding precision and long-term stability. However, there is no corresponding counterpart on the detector side up to now. The recording of light fields by CCD or CMOS cameras is always an analog process despite the fact that the camera output may be digital (CameraLink or FireWire). A new proposal is discussed in this paper that could be suited to overcome this limitation. After a brief classification of state-of-the-art systems, the author describes what he envisages being the way to future digital phase-code readings at extremely high speed and precision.