Evaluation of LCD monitors for deflectometric measurement systems

With deflectometric measurement methods there are powerful systems available today that are capable of measuring the geometry of specular surfaces or the power distribution of refractive optics in a fast and flexible manner without influencing the measurement object by tactile probing. They are based on the general principle to image a known spatially coded reference structure via the unknown measurement object onto an optically calibrated camera. As a representation of the reference structure LC-displays are very suitable as they provide a high flexibility in the generation of spatial coding patterns like sinusoidal fringes. As the characteristics of the reference structure have a huge impact on the resolution, the accuracy and the measurement range of the whole system, in this work two displays with different LCD technologies are analysed, compared and evaluated especially for deflectometric applications. The main focus is on the quality of gray-value rendering and the dependency between the characteristic curve and the observation angle. The experimental results corroborate the theoretical finding that IPS-technology is superior to TN- and MVA-displays in terms of an observation-angle independent shape of the grayscale-characteristic curve. So IPS should be the technology-of-choice when selecting a LC-display for a deflectometric measurement system.