public static function ContrastRatio($color1, $color2)
{
include_once AC_INCLUDE_PATH . "classes/ColorValue.class.php";
$color1 = new ColorValue($color1);
$color2 = new ColorValue($color2);
if (!$color1->isValid() || !$color2->isValid()) {
return true;
}
$colorR1 = $color1->getRed() / 255;
$colorG1 = $color1->getGreen() / 255;
$colorB1 = $color1->getBlue() / 255;
$colorR2 = $color2->getRed() / 255;
$colorG2 = $color2->getGreen() / 255;
$colorB2 = $color2->getBlue() / 255;
if ($colorR1 <= 0.03928) {
$colorR1 = $colorR1 / 12.92;
} else {
$colorR1 = pow(($colorR1 + 0.055) / 1.055, 2.4);
}
if ($colorG1 <= 0.03928) {
$colorG1 = $colorG1 / 12.92;
} else {
$colorG1 = pow(($colorG1 + 0.055) / 1.055, 2.4);
}
if ($colorB1 <= 0.03928) {
$colorB1 = $colorB1 / 12.92;
} else {
$colorB1 = pow(($colorB1 + 0.055) / 1.055, 2.4);
}
if ($colorR2 <= 0.03928) {
$colorR2 = $colorR2 / 12.92;
} else {
$colorR2 = pow(($colorR2 + 0.055) / 1.055, 2.4);
}
if ($colorG2 <= 0.03928) {
$colorG2 = $colorG2 / 12.92;
} else {
$colorG2 = pow(($colorG2 + 0.055) / 1.055, 2.4);
}
if ($colorB2 <= 0.03928) {
$colorB2 = $colorB2 / 12.92;
} else {
$colorB2 = pow(($colorB2 + 0.055) / 1.055, 2.4);
}
$Lum1 = $colorR1 * 0.2126 + $colorG1 * 0.7151999999999999 + $colorB1 * 0.0722;
$Lum2 = $colorR2 * 0.2126 + $colorG2 * 0.7151999999999999 + $colorB2 * 0.0722;
$ContrastRatio = 0;
if ($Lum1 > $Lum2) {
$ContrastRatio = ($Lum1 + 0.05) / ($Lum2 + 0.05);
} else {
$ContrastRatio = ($Lum2 + 0.05) / ($Lum1 + 0.05);
}
return $ContrastRatio;
}
/**
* Check if the luminosity contrast ratio between $color1 and $color2 is at least 5:1
* Input: color values to compare: $color1 & $color2. Color value can be one of: rgb(x,x,x), #xxxxxx, colorname
* Return: true or false
*/
public static function hasGoodContrastWaiert($color1, $color2)
{
include_once AC_INCLUDE_PATH . "classes/ColorValue.class.php";
$color1 = new ColorValue($color1);
$color2 = new ColorValue($color2);
if (!$color1->isValid() || !$color2->isValid()) {
return true;
}
$colorR1 = $color1->getRed();
$colorG1 = $color1->getGreen();
$colorB1 = $color1->getBlue();
$colorR2 = $color2->getRed();
$colorG2 = $color2->getGreen();
$colorB2 = $color2->getBlue();
$brightness1 = ($colorR1 * 299 + $colorG1 * 587 + $colorB1 * 114) / 1000;
$brightness2 = ($colorR2 * 299 + $colorG2 * 587 + $colorB2 * 114) / 1000;
$difference = 0;
if ($brightness1 > $brightness2) {
$difference = $brightness1 - $brightness2;
} else {
$difference = $brightness2 - $brightness1;
}
if ($difference < 125) {
return false;
}
// calculate the color difference
$difference = 0;
// red
if ($colorR1 > $colorR2) {
$difference = $colorR1 - $colorR2;
} else {
$difference = $colorR2 - $colorR1;
}
// green
if ($colorG1 > $colorG2) {
$difference += $colorG1 - $colorG2;
} else {
$difference += $colorG2 - $colorG1;
}
// blue
if ($colorB1 > $colorB2) {
$difference += $colorB1 - $colorB2;
} else {
$difference += $colorB2 - $colorB1;
}
return $difference > 499;
}
