objective-c的实现

+ (UIColor*) getContrastColor:(UIColor*) color {
    CGFloat red, green, blue, alpha;
    [color getRed:&red green:&green blue:&blue alpha:&alpha];
    double a = ( 0.299 * red + 0.587 * green + 0.114 * blue);
    return (a > 0.5) ? [[UIColor alloc]initWithRed:0 green:0 blue:0 alpha:1] : [[UIColor alloc]initWithRed:255 green:255 blue:255 alpha:1];
}

我有同样的问题，但我必须在PHP开发它。我用了@Garek的解决方案，我也用了这个答案: 转换十六进制颜色到RGB值在PHP转换十六进制颜色代码到RGB。

所以我要分享它。

我想在给定的背景颜色下使用这个函数，但不总是从“#”开始。

//So it can be used like this way:
$color = calculateColor('#804040');
echo $color;

//or even this way:
$color = calculateColor('D79C44');
echo '<br/>'.$color;

function calculateColor($bgColor){
    //ensure that the color code will not have # in the beginning
    $bgColor = str_replace('#','',$bgColor);
    //now just add it
    $hex = '#'.$bgColor;
    list($r, $g, $b) = sscanf($hex, "#%02x%02x%02x");
    $color = 1 - ( 0.299 * $r + 0.587 * $g + 0.114 * $b)/255;

    if ($color < 0.5)
        $color = '#000000'; // bright colors - black font
    else
        $color = '#ffffff'; // dark colors - white font

    return $color;
}

您可以在任何色相背景上有任何色相文本，并确保它是易读的。我一直都这么做。在Javascript中有一个关于可读的彩色文本的公式- STW* 正如它在那个链接上所说的那样，这个公式是逆伽马调整计算的变化，尽管IMHO更易于管理。 该链接右侧的菜单及其相关页面使用随机生成的颜色作为文本和背景，始终清晰可辨。所以，是的，显然这是可以做到的，没有问题。

请注意，在谷歌闭包库中有一个算法，该算法引用了w3c推荐:http://www.w3.org/TR/AERT#color-contrast。但是，在这个API中，您提供了一个建议颜色列表作为起点。

/**
 * Find the "best" (highest-contrast) of the suggested colors for the prime
 * color. Uses W3C formula for judging readability and visual accessibility:
 * http://www.w3.org/TR/AERT#color-contrast
 * @param {goog.color.Rgb} prime Color represented as a rgb array.
 * @param {Array<goog.color.Rgb>} suggestions Array of colors,
 *     each representing a rgb array.
 * @return {!goog.color.Rgb} Highest-contrast color represented by an array.
 */
goog.color.highContrast = function(prime, suggestions) {
  var suggestionsWithDiff = [];
  for (var i = 0; i < suggestions.length; i++) {
    suggestionsWithDiff.push({
      color: suggestions[i],
      diff: goog.color.yiqBrightnessDiff_(suggestions[i], prime) +
          goog.color.colorDiff_(suggestions[i], prime)
    });
  }
  suggestionsWithDiff.sort(function(a, b) { return b.diff - a.diff; });
  return suggestionsWithDiff[0].color;
};


/**
 * Calculate brightness of a color according to YIQ formula (brightness is Y).
 * More info on YIQ here: http://en.wikipedia.org/wiki/YIQ. Helper method for
 * goog.color.highContrast()
 * @param {goog.color.Rgb} rgb Color represented by a rgb array.
 * @return {number} brightness (Y).
 * @private
 */
goog.color.yiqBrightness_ = function(rgb) {
  return Math.round((rgb[0] * 299 + rgb[1] * 587 + rgb[2] * 114) / 1000);
};


/**
 * Calculate difference in brightness of two colors. Helper method for
 * goog.color.highContrast()
 * @param {goog.color.Rgb} rgb1 Color represented by a rgb array.
 * @param {goog.color.Rgb} rgb2 Color represented by a rgb array.
 * @return {number} Brightness difference.
 * @private
 */
goog.color.yiqBrightnessDiff_ = function(rgb1, rgb2) {
  return Math.abs(
      goog.color.yiqBrightness_(rgb1) - goog.color.yiqBrightness_(rgb2));
};


/**
 * Calculate color difference between two colors. Helper method for
 * goog.color.highContrast()
 * @param {goog.color.Rgb} rgb1 Color represented by a rgb array.
 * @param {goog.color.Rgb} rgb2 Color represented by a rgb array.
 * @return {number} Color difference.
 * @private
 */
goog.color.colorDiff_ = function(rgb1, rgb2) {
  return Math.abs(rgb1[0] - rgb2[0]) + Math.abs(rgb1[1] - rgb2[1]) +
      Math.abs(rgb1[2] - rgb2[2]);
};

objective-c的实现

+ (UIColor*) getContrastColor:(UIColor*) color {
    CGFloat red, green, blue, alpha;
    [color getRed:&red green:&green blue:&blue alpha:&alpha];
    double a = ( 0.299 * red + 0.587 * green + 0.114 * blue);
    return (a > 0.5) ? [[UIColor alloc]initWithRed:0 green:0 blue:0 alpha:1] : [[UIColor alloc]initWithRed:255 green:255 blue:255 alpha:1];
}

一个Android版本，捕捉alpha以及。

(感谢@thomas-vos)

/**
 * Returns a colour best suited to contrast with the input colour.
 *
 * @param colour
 * @return
 */
@ColorInt
public static int contrastingColour(@ColorInt int colour) {
    // XXX https://stackoverflow.com/questions/1855884/determine-font-color-based-on-background-color

    // Counting the perceptive luminance - human eye favors green color...
    double a = 1 - (0.299 * Color.red(colour) + 0.587 * Color.green(colour) + 0.114 * Color.blue(colour)) / 255;
    int alpha = Color.alpha(colour);

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

    return Color.argb(alpha, d, d, d);
}