bgauthier · January 26, 2017 05:53 · May 7, 2013
diff --git a/color_luminance.php b/color_luminance.php
@@ -0,0 +1,27 @@
+<?php
+/**
+ * Lightens/darkens a given colour (hex format), returning the altered colour in hex format.7
+ * @param str $hex Colour as hexadecimal (with or without hash);
+ * @percent float $percent Decimal ( 0.2 = lighten by 20%(), -0.4 = darken by 40%() )
+ * @return str Lightened/Darkend colour as hexadecimal (with hash);
+ */
+function color_luminance( $hex, $percent ) {
+
+	// validate hex string
+
+	$hex = preg_replace( '/[^0-9a-f]/i', '', $hex );
+	$new_hex = '#';
+
+	if ( strlen( $hex ) < 6 ) {
+		$hex = $hex[0] + $hex[0] + $hex[1] + $hex[1] + $hex[2] + $hex[2];
+	}
+
+	// convert to decimal and change luminosity
+	for ($i = 0; $i < 3; $i++) {
+		$dec = hexdec( substr( $hex, $i*2, 2 ) );
+		$dec = min( max( 0, $dec + $dec * $percent ), 255 ); 
+		$new_hex .= str_pad( dechex( $dec ) , 2, 0, STR_PAD_LEFT );
+	}		
+
+	return $new_hex;
+}