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
還有我對這兩個空間的理解准嗎
https://en.wikipedia.org/wiki/CIE_1931_color_space
我終於明白了
CIExyz和 CIErgb空間轉換的事情
為什么可以線性變換
變換矩陣怎么得到
xyz空間 與平面x+y+z=1 相交（不嚴謹大概是這個意思 ）得到上圖的藍色三角形
里面紫色三角形的三個頂點 某組rgb primitive 比如srgb 的假設這三個點是abc 位於 x+y+z=1這個平面上
向量oa ob oc（原點o）
作為新的基底組成的空間和原xyz空間 是線性關系
但是oa ob oc實際上不是CIE的 rgb空間 還需要scaler一下
方向是對的 系數不對
要縮放多少 需要用white來算
white 定義了 scalor
感覺white 的y=1 所有顏色加起來=1這個事情 是xyz本身定義的
這里還需要再看下資料
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.
但我倒是可以理解為什么 所有顏色加起來是luminance 因為
人眼就三種感受器 他們感受的simulus加起來就是總的感知到的luminance了
得到縮放后新的ABC
構成的空間就是rgb空間了
下圖六面體
推導如下，感謝lele分享
上面是空間轉換的問題
對於cie xyz空間本身的定義的理解可以參見wiki的這段
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定義成亮度
xz就是這個亮度下所有可能的色度，估計看着直觀吧