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Photogrammetric determination of the refractive properties of liquid crystal displays

Abstract In phase-measuring deflectometry for measuring reflecting and transparent surfaces, a high-contrast pattern displayed on a liquid crystal screen is usually optically detected. One of the most important non-idealities of liquid crystal displays with regard to the achievable measurement uncertainty is the refraction in the glass substrate, which leads to an angle-dependent offset between the actual location and the observed location of a feature displayed on the screen. Owing to the typical thicknesses and refractive indices of the glass substrates used, this offset reaches several tenths of a millimeter even at moderate viewing angles. In the approach presented here, the refraction-related offset of features displayed on the screen is determined by simultaneous observation of displayed features and features mounted on the screen. The model used so far was improved, so that apart from a distance of the features to be determined before the evaluation no further previous knowledge is necessary. Within the scope of the investigations carried out, statements on the measurement uncertainty of the method could also be made and verified for the first time.