Determine font color based on background color

Given a system (a website for instance) that lets a user customize the background color for some section but not the font color (to keep number of options to a minimum), is there a way to programmatically determine if a "light" or "dark" font color is necessary?

I'm sure there is some algorithm, but I don't know enough about colors, luminosity, etc to figure it out on my own.

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I encountered similar problem. I had to find a good method of selecting contrastive font color to display text labels on colorscales/heatmaps. It had to be universal method and generated color had to be "good looking", which means that simple generating complementary color was not good solution - sometimes it generated strange, very intensive colors that were hard to watch and read.

After long hours of testing and trying to solve this problem, I found out that the best solution is to select white font for "dark" colors, and black font for "bright" colors.

Here's an example of function I am using in C#:

Color ContrastColor(Color color)
{
    int d = 0;

    // Counting the perceptive luminance - human eye favors green color... 
    double a = 1 - ( 0.299 * color.R + 0.587 * color.G + 0.114 * color.B)/255;

    if (a < 0.5)
       d = 0; // bright colors - black font
    else
       d = 255; // dark colors - white font

    return  Color.FromArgb(d, d, d);
}

This was tested for many various colorscales (rainbow, grayscale, heat, ice, and many others) and is the only "universal" method I found out.

Edit
Changed the formula of counting a to "perceptive luminance" - it really looks better! Already implemented it in my software, looks great.

Edit 2 @WebSeed provided a great working example of this algorithm: http://codepen.io/WebSeed/full/pvgqEq/

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Thank you @Gacek. Here's a version for Android:

@ColorInt
public static int getContrastColor(@ColorInt int color) {
    // Counting the perceptive luminance - human eye favors green color...
    double a = 1 - (0.299 * Color.red(color) + 0.587 * Color.green(color) + 0.114 * Color.blue(color)) / 255;

    int d;
    if (a < 0.5) {
        d = 0; // bright colors - black font
    } else {
        d = 255; // dark colors - white font
    }

    return Color.rgb(d, d, d);
}

And an improved (shorter) version:

@ColorInt
public static int getContrastColor(@ColorInt int color) {
    // Counting the perceptive luminance - human eye favors green color...
    double a = 1 - (0.299 * Color.red(color) + 0.587 * Color.green(color) + 0.114 * Color.blue(color)) / 255;
    return a < 0.5 ? Color.BLACK : Color.WHITE;
}

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This is such a helpful answer. Thanks for it!

I'd like to share an SCSS version:

@function is-color-light( $color ) {

  // Get the components of the specified color
  $red: red( $color );
  $green: green( $color );
  $blue: blue( $color );

  // Compute the perceptive luminance, keeping
  // in mind that the human eye favors green.
  $l: 1 - ( 0.299 * $red + 0.587 * $green + 0.114 * $blue ) / 255;
  @return ( $l < 0.5 );

}

Now figuring out how to use the algorithm to auto-create hover colors for menu links. Light headers get a darker hover, and vice-versa.

链接地址: http://www.djcxy.com/p/2498.html

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