A photographic technique for assessing the viewing-angle performance of liquid-crystal displays

Liquid-crystal displays (LCDs) have notable variation in luminance and perceived contrast as a function of the angle from which they are viewed. Though this is an important performance issue for LCDs, most evaluation techniques for assessing this variation have been limited to laboratory settings. This study demonstrates the use of a photographic technique for such an evaluation. The technique is based on an actively cooled charge-coupled-device (CCD) detector in combination with a macro lens covering a circular angular range (theta) of +/-42.5 degrees. The camera was used to evaluate the luminance and perceived contrast properties of an LCD. Uniform field images corresponding to 17 equally spaced gray-scale values in the digital driving level (DDL) range of the display system were acquired. The 12-bit gray-scale digital images produced by the camera were converted to luminance units (cd/m(2)) via the measured luminance vs. DDL response function of the camera. The changes in perceived contrast as a function of viewing angle were derived from the Barten model of the gray-scale response of the human-visual system using the methods proposed by the AAPM TG18 Report. The results of this photographic technique were compared to measurements acquired from a similar display using a Fourier-optics-based luminance meter. The results of the two methods generally agreed to within 5%. The photographic methods used were found to be accurate and robust for in-field assessment of the angular response of LCDs over the FOV of the camera.