Abstract

Pelli and Zhang¹ describe techniques for combining the outputs of the three color DACs with a CRT monitor to achieve extra gray-scale resolution, particularly at low contrast levels. While there should theoretically be 24 bits of gray scale available, this is unachievable in practice because of monitor nonlinearities and DAC inaccuracies. We measure and account for the inaccuracies in the DAC (which are extremely stable) and build a single look-up table containing over 32,000 (15 bits) RGB values that are converted by a passive resistive circuit into equal-interval gray-scale values. Dynamic inaccuracies resulting from DAC bit changes have been examined and found to be negligible. A novel smoothing technique that does not depend on assumptions of the form of the monitor non-linearity has been used. The final correlation of measured vs. specified luminance has been as high as 0.999996 (and is typically higher than 0.99995).

© 1992 Optical Society of America