Practical Aspects of Grayscale Calibration of Display Systems

摘要

Five aspects of grayscale calibration of display systems are discussed: 1) As has been shown before, it is very desirable that the discrete luminance levels on the calibrated display function are placed with high accuracy. The accuracy of a calibration with a commercial system is demonstrated. The effect of 8-bit versus 10-bit precision in computing the required luminance levels on contrast and noise in images is illustrated. 2) Display controllers of liquid crystal displays (LCDs) predominantly offer 8-bit precision. A subpixel modulation technique to increase the grayscale accuracy is presented. 3) LCDs may exhibit characteristic curves with non-monotonically changing first derivatives. To achieve a high degree of calibration accuracy, these curves must be represented by a sufficient number of strategically placed measurement points. 4) Photometers of commercial calibration systems for CRT monitors have wide acceptance angles. For display systems with non-uniform angular emission distribution, these photometers may indicate luminance values that do not represent the luminance perceived through the small acceptance angle of the eyes of observers. Techniques for adapting these photometers to luminance measurements for liquid crystal displays are proposed. 5) The suitability of built-in photo-sensors (attached to the tapered glass envelope of the CRT) for calibrating a monitor according to the DICOM Display Function Standard is investigated. Considering the solutions to these problems, more accurate grayscale calibration, especially to the DICOM Display Function Standard, can be implemented for a wide variety of display systems.