Estimating black-level emissions of computer-controlled displays

It is quite common for computer-controlled displays to emit light in image areas set to digital values of zero, referred to as their black level. This is expected for liquid-crystal displays and also can occur for cathode-ray tube displays when the "brightness" (gun-amplifier offset) is set excessively high. For either display, the light emission at the black level results in color channels whose chromaticities vary with luminance level. Consequently, typical methods of colorimetric characterization result in large error. When this black-level emission is measured and accounted for suitably, characterization accuracy is dramatically improved. Unfortunately, many instruments used to measure displays have too low a sensitivity to measure black-level emission with sufficient precision and accuracy. A method of estimating black-level emissions was derived and tested. Because the optimal black-level results in channel chromaticities that are invariant to the greatest extent with luminance level, an objective function was defined as the sum of chromaticity variances of each channel over a range of measurements. Minimizing this objective function resulted is an estimate of a display's black level. The estimated black level resulted in equivalent or superior performance to direct measurements. (C) 2003 Wiley Periodicals, Inc.