根据 WCAG 规范，其计算公式为 ，L1/L2 为二者的明亮度(Luminance)。以下为实时计算公式
(0.2990019093583774 + 0.05) / (0.08716187250404345 + 0.05) = 2.5444527913403125
the relative brightness of any point in a colorspace, normalized to 0 for darkest black and 1 for lightest white
Note 1: For the sRGB colorspace, the relative luminance of a color is defined as where R, G and B are defined
and RsRGB, GsRGB, and BsRGB are defined as:
The "^" character is the exponentiation operator. (Formula taken from [sRGB] and [IEC-4WD]).
Note 2: Almost all systems used today to view Web content assume sRGB encoding. Unless it is known that another color space will be used to process and display the content, authors should evaluate using sRGB colorspace. If using other color spaces, see Understanding Success Criterion 1.4.3.
Note 3: If dithering occurs after delivery, then the source color value is used. For colors that are dithered at the source, the average values of the colors that are dithered should be used (average R, average G, and average B).
Note 4: Tools are available that automatically do the calculations when testing contrast and flash.
Note 5: A MathML version of the relative luminance definition is available.