color space

在微软网站可下载免费的DisplayHDR Test: The tool allows users to confirm the display parameters including brightness, color and contrast performance of High Dynamic Range (HDR) laptop and desktop monitors as per [根据] the set forth [阐述] in VESA’s High-Performance Monitor and Display Compliance Test Specification (DisplayHDR). 测试结果：

sRGB is a standard RGB color space that HP and Microsoft created cooperatively in 1996 to use on monitors, printers, and the Web. 注意min, max effective value分别是15和250.

  

程序未能获得硬件信息，以上数据是默认/猜的数据。比如VESA统计了若干台常见的显示器，取了个平均值之类。

颜色空间的空间和线性空间的空间一个意思。颜色空间涉及颜色的表示和呈现。3x8位不够好，有3x10位。3个double估计过了。显示器可能把[15, 15, 15]和[16, 16, 16]显示为同一种颜色。显示为不同颜色，(我的)眼睛分辨不出。请注意gamut [范围] coverage. primary: (三)原色。

买个高档数码单反(和若干镜头)，用AdobeRGB和RAW格式，自用的显示器也高档，很有意思吗？给网民都配上高档显示器才是真厉害。花公家十来万买摄影器材，拍了几十年如下风格：

就厉害啦？知道挖掘机多少钱一台不？能用挖掘机开酒瓶不？:-) 用800/f 2拍男足，它们就不输球了？我知道没这么厉害的镜头。

 

The Adobe RGB color space was developed in 1998. It was designed to encompass most of the colors achievable on CMYK color printers, but by using RGB primary colors on a device such as a computer display. To meet the color appearance requirements of the color space, the luminance of the monitor must be 160.00 cd/m² at the white point, and 0.5557 cd/m² at the black point, which implies a contrast ratio of 287.9.

尼特(nit)与勒克斯(lux, lx)的转换

The CIE XYZ color space encompasses all color sensations that are visible to a person with average eyesight. That is why CIE XYZ (Tristimulus values) is a device-invariant representation of color. It serves as a standard reference against which many other color spaces are defined. 

The CIE 1931 RGB color space and CIE 1931 XYZ color space were created by the International Commission on Illumination (CIE; 国际照明委员会) in 1931. They resulted from a series of experiments done in the late 1920s by William David Wright using ten observers and John Guild using seven observers. The experimental results were combined into the specification of the CIE RGB color space, from which the CIE XYZ color space was derived. The CIE 1931 color spaces are still widely used.

The experiments were conducted by using a circular split screen 2 degrees in diameter, which is the angular size of the human fovea [视网膜中间的凹]. On one side a test color was projected while on the other an observer-adjustable color was projected. The adjustable color was a mixture of three primary colors, each with fixed chromaticity [色度], but with adjustable brightness. The observer would alter the brightness of each of the three primary beams until a match to the test color was observed.

Although the experiments were carried out using various primaries at various intensities, and although they used a number of different observers, all of their results were summarized by the standardized CIE RGB color matching functions, obtained using three monochromatic primaries at standardized wavelengths of 700 nm (red), 546.1 nm (green) and 435.8 nm (blue).

X,Y,Z写不出表达式，只好罗列数据。Table lookup can become impractical for some computational tasks. Instead of referring to the published table, the CIE XYZ color matching functions can be approximated by a sum of Gaussian functions.

把颜色空间画成个长方体的话，我们看不到内部。

这篇文章提到：By construction x+y+z=1, so z=1-x-y and all the information of the chromaticity coordinates is contained in the pair (x,y). Therefore, all the possible chromaticities can be represented in a 2D plane, the plane with axes x and y, and this is called the CIE xy chromaticity diagram.

The X and Z tristimulus [三(色)刺激] values can be calculated back from the chromaticity values x and y and the Y tristimulus value:

 

也许是指定/固定某个亮度Y(常数)，改变/列举X和Z，得到x和y.

人眼对绿色最敏感，RGB转YUV，算Y时G的权重最大：

• Y = 0.299R + 0.587G + 0.114B
• U = 0.492 (B - Y)
• V = 0.877 (R - Y)

CIE当初随手用了XYZ，YUV的Y抄了CIE的Y，U和V也是两个连续的字母，YUV比YVW念起来上口。此UV和紫外线Ultra Violet没关系。

B - Y; R - Y; 于是有了色差这个词。YCbCr的b和r分别代表blue和red. complementary color: color of light which when combined with a given colour makes white light (eg blue with yellow) 互补色（混合后产生白色光的两种色光, 如蓝和黄)。

为啥人眼对绿色敏感？

首先绿色的波长不短不长。其次我们的祖先猿吃绿色食物，不仅需要发现绿色，还要能区分各种绿色：菠菜绿、苦瓜绿……

红绿蓝的排名顺序咋来的？没有光谱图还有彩虹。赤橙黄绿青蓝紫，红橙黄绿青蓝紫，红橙黄绿蓝靛紫，春来江水绿如蓝。可见用数字表示颜色很有必要。