function setBrightness(&$r, &$g, &$b, $value)
    {
        $Y  = ceil(  0 . 299   * $r +  0 . 587   * $g +  0 . 114  * $b); 
        $Cb = ceil(- 0 . 1687  * $r -  0 . 3313  * $g +  0 . 5    * $b +  128 . 0 );
        $Cr = ceil(  0 . 5     * $r -  0 . 4187  * $g -  0 . 0813  * $b +  128 . 0 );

        $Y += $value;

        $b  = ceil($Y +  1 . 772  * ($Cb -  128 . 0 ));
        if ($b >  255 ) $b =  255 ; else if ($b <  0 ) $b =  0 ;

        $g = ceil($Y -  0 . 34414  * ($Cb -  128 . 0 ) -  0 . 71414  * ($Cr -  128 . 0 ));
        if ($g >  255 ) $g =  255 ; else if ($g <  0 ) $g =  0 ;

        $r = ceil($Y +  1 . 402  * ($Cr -  128 . 0 ));
        if ($r >  255 ) $r =  255 ; else if ($r <  0 ) $r =  0 ;
    }