给定背景颜色，如何获得前景色，使其可读的背景颜色？ [英] given a background color, how to get a foreground color that make it readable on that background color?
问题描述
给定背景颜色，如何获得前景色，使其在背景色上可读？
ps：我的意思是在程序中自动计算前景色。
或简化问题，如果前景颜色选自白色/空白，如何在程序中做选择？
<最安全的做法是遵守万维网联盟（W3C）Web内容无障碍指南2.0，该指南规定了亮度 www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-contrast.htmlrel =nofollow noreferrer>正常文字（12 pt或更小）的对比度为4.5：1，以及3.0：1大文字。对比度定义为：
[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。
通过首先将每个颜色的RGB值转换为伽马调整的归一化rgb值：
- r =（R / 255）^ 2.2
- b =（B / 255）^ 2.2
- g =（G / 255）^ 2.2
然后使用sRGB常数（四舍五入为4）组合它们：
Y = 0.2126 * r + 0.7151 * g + 0.0721 * b
这使得白色的Y为1，黑色的Y为0，所以最大可能的对比度为（1.05 / 0.05）= 21（舍入误差范围内）。
此计算假设在相对昏暗的房间（或房间，如果她或他必须让用户可以变暗）的标准执行监视器。这使得它适合家庭或办公室使用，但我不知道它是否足以用于户外使用的移动应用或其他设备。
given a background color, how to get a foreground color that make it readable on that background color?
ps: I mean computing that foreground color automatically in a program.
or simplify the problem, if the foreground color is chosen from white/blank, how to do the choise in a program?
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]
Where Y(b) is the brightness (luminance) of the brighter color and Y(d) is the brightness of the darker color.
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
Then combine them using sRGB constants (rounded to 4 places):
Y = 0.2126*r + 0.7151*g + 0.0721*b
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).
Or let JuicyStudio do the math for you.
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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