Compressive Schlieren Deflectometry

TL;DR

This paper introduces a novel optical compressive sensing method for efficiently capturing and reconstructing deflection spectra in Schlieren deflectometry, enabling faster and more direct analysis of transparent surfaces.

Contribution

It presents a new optical compressive sensing approach using spread spectrum techniques and a spatial light modulator to acquire deflection spectra with fewer measurements.

Findings

Successful experimental validation on test objects

Key deflection parameters can be directly computed from measurements

Method reduces data acquisition and processing complexity

Abstract

Schlieren deflectometry aims at characterizing the deflections undergone by refracted incident light rays at any surface point of a transparent object. For smooth surfaces, each surface location is actually associated with a sparse deflection map (or spectrum). This paper presents a novel method to compressively acquire and reconstruct such spectra. This is achieved by altering the way deflection information is captured in a common Schlieren Deflectometer, i.e., the deflection spectra are indirectly observed by the principle of spread spectrum compressed sensing. These observations are realized optically using a 2-D Spatial Light Modulator (SLM) adjusted to the corresponding sensing basis and whose modulations encode the light deviation subsequently recorded by a CCD camera. The efficiency of this approach is demonstrated experimentally on the observation of few test objects. Further, using a simple parametrization of the deflection spectra we show that relevant key parameters can be directly computed using the measurements, avoiding full reconstruction.