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# Lab Color and Color Profile

## Human Eye Cells 

Peak Wavelength:\\
- Blue: 450nm   Green:550nm   Red:600nm\\
- Rod cell: 510nm (380~590nm blue~green)



## CIE Lab Color

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.[Wikipedia](https://en.wikipedia.org/wiki/CIE_1931_color_space#Meaning_of_X,_Y_and_Z)

**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](https://en.wikipedia.org/wiki/CIE_1931_color_space#CIE_xy_chromaticity_diagram_and_the_CIE_xyY_color_space)

**Yuv coordinate:** Similar with Yxy, YUV is a color encoding system typically used as part of a color image pipeline. Y′ stands for the luma component (the brightness) and U and V are the chrominance (color) components. [wiki CIE 1960](https://en.wikipedia.org/wiki/CIE_1960_color_space) [wiki YUV](https://en.wikipedia.org/wiki/YUV)


**Lab coordinate:** also means to seperate luminance with chromatic. Strongly influenced by the Munsell color system, the intention behind CIELAB was to create a space that can be computed via simple formulas from the CIEXYZ space but is <color /#FFff00>more perceptually uniform</color> than CIEXYZ.
While CIELAB has a relative white point, the International Color Consortium L*a*b* values are relative to CIE standard illuminant D50, while they are relative to the unprinted substrate for other rendering intents).

**Luv coordinate:** similar with Lab. The CIE 1976 (L\*, u\*, v\*) color space (a.k.a. CIELUV), preserves the same L\* as L\*a\*b\* but has a different representation of the chromaticity components. 

<wrap lo>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\\
 * CIE 1931 color space (XYZ): https://en.wikipedia.org/wiki/CIE_1931_color_space\\
 * CIELAB color space: https://en.wikipedia.org/wiki/CIELAB_color_space\\
 * Munsell Color System: https://en.wikipedia.org/wiki/Munsell_color_system\\
 * Patablog Colorimetry: https://patapom.com/blog/Colorimetry/ColorSpace\\
</wrap>


## Conversion of Color Represents

**RGB and HSL** https://stackoverflow.com/questions/39118528/rgb-to-hsl-conversion


## Display on Computer
{{::palatte_adobergb.png?40| Adobe RGB}}  Adobe RGB \\
{{:palatte_srgb.png?40| sRGB}}  sRGB

普通来说使用sRGB就可以了。因为网页和大部分显示器只支持到sRGB

使用Photoshop可以在不改变视觉颜色的情况下转换color profile。但是使用colorsync utility似乎就不行。不知道区别是什么。

### AdobeRGB display on Windows
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
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