Color Accuracy of a Calibrated Computer Monitor for Shade Replication

Objectives: To evaluate the color accuracy of a computer cathode ray tube (CRT) monitor after a proposed calibration protocol for the purpose of shade replication. Methods: An IBM compatible computer and a 22 inch CRT monitor with 24 bit color quality were used. The calibration protocol consisted of RGB values (0 to 255) normalized and defined with a minimum of 0 and a maximum of 1. Eleven images from 0 to 1 with an interval of 0.1 were created to express red (R), green (G) and blue (B) phosphors individually, resulting in a total of 33 different colors. Matlab?was used to display the 33 color images on the monitor, and color measurements were carried out with a spectroradiometer. The monitor’s gamma for each phosphor was then plotted, and a correction formula was established by mathematically inversing the gamma plots. The color accuracy of this calibration protocol was evaluated using 22 well spaced color samples from two groups: (1) located within the tooth color space, e.g. shade tabs, and (2) covering a wider color space (Kodak Q60). The actual RGB values of the 44 samples were measured with a spectroradiometer and then created on the monitor. The spectroradiometer was used to measure the color on the monitor. The mean color difference (Delta E) was calculated between the actual and created color on the monitor for both sample sets. The data was analyzed using a Wilcoxon Rank-Sum test. Results: The mean Delta E for the shade tab group was 1.44 (0.35) and Kodak Q60 group was 5.00 (3.67). A statistically significant difference was found between the two groups (p<0.001). Conclusion: The calibrated monitor produced colors within the tooth color space more accurately than colors in a wider color space. Supported by: NIH R15 EY013527 and an ACP Research Fellowship in Geriatric Prosthodontics.