Accurate Measurement of Monochrome Luminance Palettes for the Calibration of Medical LCD Monitors

摘要

Grayscale medical monitors are commonly calibrated by transforming the image display values sent to a graphic controller using a lookup table (LUT). The calibration LUT is deduced from the uncalibrated luminance response (uLR) of the display system. The uLR of liquid crystal display (LCD) systems is poorly behaved with significant discontinuities occurring in the relative luminance changes. Accurate grayscale calibration of LCD devices thus requires a measurement of the luminance for the full palette of possible output values. A method is reported to acquire the uLR of LCD displays, generate a LUT to achieve precise calibration, and assess the accuracy of the calibration results. A palette of 766 luminance values can be measured in 12 minutes. The accuracy of the method permits the evaluation of relative luminance changes, dL/L, to be made with a precision of .0002 to .0007 for luminance values between 1000 and 1 cd/m~2. For seven LCD monitors, 766 values for the uLR were measured and calibration tables deduced. The calibrated luminance response (cLR) for 256 gray values was then compared to the DICOM standard. The root mean squared error of the observed JNDs per luminance interval values ranged from .37 to .59 which is less than the AAPM recommended value of 1.0. A full calibration of this type should be done at installation. However, the stability of LCD systems suggests that periodic recalibration will not be necessary.