给定背景色,如何获得使其在该背景色上可读的前景色? [英] Given a background color, how to get a foreground color that makes it readable on that background color?
问题描述
给出背景色,如何获得使其在该背景色上可读的前景色?
我的意思是在程序中自动计算该前景色。 / p>
还是简化问题,如果从白色/黑色中选择了前景色,如何在程序中进行选择?
最安全的选择是遵守万维网联盟(W3C)的Web内容可访问性指南2.0,该指南指定了常规文本(12磅或更小)的对比度为4.5:1,大文本为3.0:1 。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。
您可以计算亮度Y首先将每种颜色的RGB值转换为伽玛调整后的归一化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)组合它们:
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(在四舍五入误差内)。 / p>
此计算假设在光线较暗的房间(或房间t使用者可以根据需要调暗帽子)。这足以满足家庭或办公室使用需求,但我不知道它是否适合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 makes it readable on that background color?
I mean computing that foreground color automatically in a program.
Or simplify the problem, if the foreground color is chosen from white/black, how to do the choice 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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