The patience limit (PL) and just noticeable difference (JND) of various grayscale viewing angle characteristics were evaluated subjectively using simulated images. Ten test subjects evaluated four types of picture images. Each type consisted of eight different images; two kinds of reverse images, three kinds of black crushing images, and three kinds of white omission images. All the images had several grayscale difference levels. The results showed that the concernments depend not only on the kind of pictures but also significantly on the images. We propose a new evaluation criterion, criterion grayscale difference odiousness (CGDO) value, for evaluating grayscale viewing angle characteristics. The value is calculated integrating the gamma-curve shape and the difference in the grayscale level from the original one. In our results, the CGDO values at PL and JND are about 2.0 and 0.5, respectively. Therefore the CGDO values shall be 2.0 or less, and should be 0.5 or less for ideal TFT-LCD legibility.
