给定背景颜色，如何获得使其在该背景颜色上可读的前景色? [英] Given a background color, how to get a foreground color that makes it readable on that background color?
问题描述
给定背景颜色，如何获得使其在该背景颜色上可读的前景色?
Given a background color, how to get a foreground color that makes it readable on that background color?
我的意思是在程序中自动计算前景色.
I mean computing that foreground color automatically in a program.
或者简化问题，如果前景色是从白/黑中选择，在程序中如何选择?
Or simplify the problem, if the foreground color is chosen from white/black, how to do the choice in a program?
推荐答案
最安全的选择是符合万维网联盟 (W3C) 的 Web 内容可访问性指南 2.0，该指南指定了亮度 常规文本的对比度为 4.5:1(12 pt 或更小)，对比度为 3.0:1大文本.对比度定义为:
The safest bet is to conform with the World Wide Web Consortium’s (W3C) Web Content Accessibility Guidelines 2.0, which specify a brightness contrast ratio of 4.5:1 for regular text (12 pt or smaller), and 3.0:1 for large text. Contrast ratio is defined as:
[Y(b) + 0.05]/[Y(d) + 0.05]
[Y(b) + 0.05] / [Y(d) + 0.05]
其中 Y(b) 是较亮颜色的亮度(亮度)，Y(d) 是较暗颜色的亮度.
Where Y(b) is the brightness (luminance) of the brighter color and Y(d) is the brightness of the darker color.
首先将每种颜色的 RGB 值转换为伽马调整后的归一化 rgb 值来计算亮度 Y:
You calculate luminance Y by first converting each of the color’s RGB values to gamma adjusted normalize rgb values:
- r = (R/255)^2.2
- b = (B/255)^2.2
- g = (G/255)^2.2
然后使用 sRGB 常量(四舍五入)将它们组合起来:
Then combine them using sRGB constants (rounded to 4 places):
Y = 0.2126*r + 0.7151*g + 0.0721*b
Y = 0.2126*r + 0.7151*g + 0.0721*b
这使白色的 Y 为 1，黑色的 Y 为 0，因此最大可能的对比度为 (1.05/0.05) = 21(在舍入误差范围内).
This gives white a Y of 1 and black a Y of 0, so the maximum possible contrast is (1.05/ 0.05) = 21 (within rounding error).
此计算假设在相对昏暗的房间(或用户可以在必要时调暗的房间)中使用标准性能的显示器.这使它适合家庭或办公室使用，但我不知道它是否适合户外使用的移动应用或其他设备.
This calculation assumes a standard-performing monitor in a relatively dimly lit room (or a room that the user can make dim if she or he has to). That makes it adequate for home or office use, but I don’t know if it’s adequate for mobile apps or other devices that are used outdoors.
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