In the case of the sRGB and Rec. 709 spaces, the equation is [1704]
Y = 0.2126R + 0.7152G + 0.0722B.
--realtime rendering 4th
but why
还有我对这两个空间的理解准吗
https://en.wikipedia.org/wiki/CIE_1931_color_space
我终于明白了
CIExyz和 CIErgb空间转换的事情
为什么可以线性变换
变换矩阵怎么得到
xyz空间 与平面x+y+z=1 相交（不严谨大概是这个意思 ）得到上图的蓝色三角形
里面紫色三角形的三个顶点 某组rgb primitive 比如srgb 的假设这三个点是abc 位于 x+y+z=1这个平面上
向量oa ob oc（原点o）
作为新的基底组成的空间和原xyz空间 是线性关系
但是oa ob oc实际上不是CIE的 rgb空间 还需要scaler一下
方向是对的 系数不对
要缩放多少 需要用white来算
white 定义了 scalor
感觉white 的y=1 所有颜色加起来=1这个事情 是xyz本身定义的
这里还需要再看下资料
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.
但我倒是可以理解为什么 所有颜色加起来是luminance 因为
人眼就三种感受器 他们感受的simulus加起来就是总的感知到的luminance了
得到缩放后新的ABC
构成的空间就是rgb空间了
下图六面体
推导如下，感谢lele分享
上面是空间转换的问题
对于cie xyz空间本身的定义的理解可以参见wiki的这段
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.
y定义成亮度
xz就是这个亮度下所有可能的色度，估计看着直观吧