【色彩】ICC Profile 內的 VCGT Tag

	ICC Profile 內的 VCGT Tag (Video Card Gamma Table) 是一個沒有定義在 ICC Profile Specification 內的 Tag，但現行不少用來做軟校的 ICC Profile 有包含此 Tag，該 Tag 最早被定義在何處？

定義／Definition

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在 Abhay Sharma 和 P.D. Fleming 所發表的 Measuring the quality of ICC profiles and color management software 一文中，在 Monitor profile quality 一節中，提到 vcgt 最早被應用的地方如下所述：  

"Macintosh monitor profiles are distinguished by the use of the 'vcgt' tag that is used to provide the calibration part of the system. vcgt stands for video card gamma tag and has been part of MacOS since ColorSync 2.5 (Apple, 1998). How is calibration to a user defined gamma and white point achieved? First the inherent, factory response of the system is determined. Then the software asks the user for the required gamma and white point. A correction is calculated and stored in the vcgt, such that the vcgt in conjunction with the factory response results in the user requested Gamma and white point. On selection of a monitor profile, the data from the vcgt tag is downloaded to the video card and used to actively alter the system display"

意即，從 MacOS 的 ColorSync 從版本 2.5 之後（Apple 1998），就開始支援 VCGT，並且用來校正 Gamma 和白點。