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本帖最后由 dtlnor 于 2017-10-14 03:36 编辑
Tone curve / gamma
The target response curve is normally an exponential curve (output = inputgamma), and defaults to 2.2 (which is close to a typical CRT displays real response). Four pre-defined curves can be used as well: the sRGB colorspace response curve, which is an exponent curve with a straight segment at the dark end and an overall response of approximately gamma 2.2, the L* curve, which is the response of the CIE L*a*b* perceptual colorspace, the Rec. 709 video standard response curve and the SMPTE 240M video standard response curve.
Another possible choice is “As measured”, which will skip video card gamma table (1D LUT) calibration.
Note that a real display usually can't reproduce any of the ideal pre-defined curves, since it will have a non-zero black point, whereas all the ideal curves assume zero light at zero input.
For gamma values, you can also specify whether it should be interpreted relative, meaning the gamma value provided is used to set an actual response curve in light of the non-zero black of the actual display that has the same relative output at 50% input as the ideal gamma power curve, or absolute, which allows the actual power to be specified instead, meaning that after the actual displays non-zero black is accounted for, the response at 50% input will probably not match that of the ideal power curve with that gamma value (to see this setting, you have to go into the “Options” menu, and enable “Show advanced options”).
To allow for the non-zero black level of a real display, by default the target curve values will be offset so that zero input gives the actual black level of the display (output offset). This ensures that the target curve better corresponds to the typical natural behavior of displays, but it may not be the most visually even progression from display minimum. This behavior can be changed using the black output offset option (see further below).
Also note that many color spaces are encoded with, and labelled as having a gamma of approximately 2.2 (ie. sRGB, REC 709, SMPTE 240M, Macintosh OS X 10.6), but are actually intended to be displayed on a display with a typical CRT gamma of 2.4 viewed in a darkened environment.
This is because this 2.2 gamma is a source gamma encoding in bright viewing conditions such as a television studio, while typical display viewing conditions are quite dark by comparison, and a contrast expansion of (approx.) gamma 1.1 is desirable to make the images look as intended.
So if you are displaying images encoded to the sRGB standard, or displaying video through the calibration, just setting the gamma curve to sRGB or REC 709 (respectively) is probably not what you want! What you probably want to do, is to set the gamma curve to about gamma 2.4, so that the contrast range is expanded appropriately, or alternatively use sRGB or REC 709 or a gamma of 2.2 but also specify the actual ambient viewing conditions via a light level in Lux, so that an appropriate contrast enhancement can be made during calibration. If your instrument is capable of measuring ambient light levels, then you can do so.
(For in-depth technical information about sRGB, see “A Standard Default Color Space for the Internet: sRGB” at the ICC website for details of how it is intended to be used)
If you're wondering what gamma value you should use, you can run “Report on uncalibrated display device” from the “Tools” menu to measure the approximated overall gamma among other info. Setting the gamma to the reported value can then help to reduce calibration artifacts like banding, because the adjustments needed for the video card's gamma table should not be as strong as if a gamma further away from the display's native response was chosen.
或許官方文檔對你有幫助？
如果我的英文閱讀理解不錯的話，應該是說srgb的curve在接近黑色的一端的線段是直線，但整體與gamma2.2的指數曲線差不多，大概這就是兩者調完看起來也沒什麼分別的原因把 |
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可以再请教大佬两个问题吗？
