De-pixelating phase mask for digital fringe projection

A method to reduce the influence of pixel structure in projectors based on spatial light modulators is proposed using a binary phase mask. The method is well-suited for applications utilising narrow bandwidth light sources, such as digital fringe projection. The design approach, based on the concept of a scatter plate and computer-generated hologram, is introduced, followed by simulations from a polychromatic Fourier optics model; an investigation of the fabricated mask's quality; and results from a set of projection experiments. A polychromatic Fourier optics model is used to simulate the point spread function (PSF) resulting from the phase mask design. This PSF is applied to a set of phase stepped fringe patterns acquired experimentally and indicates that the phase mask can reduce deviations from the ideal linear phase ramp due to projector pixel structure by up to 7 × . A re-focusing phenomenon similar to the Talbot effect is observed both experimentally and in the associated numerical model. Experiments with the fabricated phase mask indicate that phase noise is attenuated by up to 3 × at the plane of best focus when the phase mask is present and projected directly on to a camera sensor, and up to 2 × when the fringes are projected onto a screen and viewed with a camera. Both experiments show almost constant attenuation throughout the measured depth range. Errors in estimated surface depth due to projector pixel structure can also be reduced by up to the same factor when used in a digital fringe projection configuration.<p></p>