SYSTEMATIC ERRORS IN DEFLECTOMETY INDUCED BY USE OF LIQUID CRYSTAL DISPLAYS AS REFERENCE STRUCTURE

摘要

Deflectometric measurements are based on observing a known reference structure via the reflective or refractive surface under test. Many up-to-date deflectometry systems are using a liquid crystal display (LCD) as reference structure, as those allow a flexible pattern generation. In most of these cases the display is regarded as an ideal flat surface emitting structured light with a characteristic close to a lambert radiator. Closer observation, however, reveals that the properties and behavior of LCDs are non-ideal in a number of aspects. Therefore the insufficient consideration of the real display behavior induces systematic errors in deflectometry, which are relevant especially if the absolute shape is to be measured. The present contribution gives an overview of the main characteristics of LCDs that cause systematic errors in deflectometric shape measurements and discusses ways to improve the model description of displays used as deflectometric reference.