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Peak Wavelength:
- Rod cell: 510nm (380~590nm blue~green)
- B: 450nm G:550nm R:600nm

CIE: the International Commission on Illumination (Commission internationale de l’éclairage)
L: lightness, a: Green&Red(-128~+127), b: Blue&Yellow(-128~+127)

Most of our colour modes are based on how much of a certain colour is needed to be displayed for a certain device. For example RGB is how much Red, Green and Blue needs to be displayed to show the correct colour on a digital screen and CMYK values are for how much colour is needed for a 4 colour print. The LAB colour model is based on how humans see colour; How much colour there is on the green to red axis combined with how much colour there is on the blue to yellow axis.

XYZ coordinate: When judging the relative luminance (brightness) of different colors in well-lit situations, humans tend to perceive light within the green parts of the spectrum as brighter than red or blue light of equal power. The luminosity function that describes the perceived brightnesses of different wavelengths is thus roughly analogous to the spectral sensitivity of M cones.

The CIE model capitalizes on this fact by setting Y as luminance. Z is quasi-equal to blue, or the S cone response, and X is a mix of response curves chosen to be nonnegative. The XYZ tristimulus values are thus analogous to, but different from, the LMS cone responses of the human eye. Setting Y as luminance has the useful result that for any given Y value, the XZ plane will contain all possible chromaticities at that luminance.

The unit of the tristimulus values X, Y, and Z is often arbitrarily chosen so that Y = 1 or Y = 100 is the brightest white that a color display supports. In this case, the Y value is known as the relative luminance. The corresponding whitepoint values for X and Z can then be inferred using the standard illuminants.

Yxy coordinate: is a recombination of XYZ coordinate in order to separate luminance with chromatic. Y is luminance, same as the Y in XYZ coordinate. x-y is a mix of X-Y-Z so that it only changes chromatic. Wikipedia

参考资料：
* Lab Color Space介绍，以及如何使用Lab色彩空间快速调整特定颜色 https://www.youtube.com/watch?v=bBh3DE2OIOw&feature=youtu.be&t=24m19s
* What is Lab color: http://www.photoshopbuzz.com/what-is-lab-color-photoshop/
* Human Eye Cell Color Spectrum: https://midimagic.sgc-hosting.com/huvision.htm

Refer to these two Q&A on how to solve thr over satrauted display when using a monitor that support 100%+ sRGB.

https://answers.microsoft.com/en-us/windows/forum/all/is-the-srgb-mode-still-the-only-one-that-windows/5abf7c11-8f71-4f6d-801e-2096816f409f

https://superuser.com/questions/164793/how-can-i-reduce-saturation-on-my-wide-gamut-monitor-to-have-it-display-at-srgb