function saveImage(){
    //magic...
    define('UPLOAD_DIR', '../webroot/img/');
    $base64string = str_replace('data:image/png;base64,', '', $base64string);
    $base64string = str_replace(' ', '+', $base64string);
    $data = base64_decode($base64string);
    $id = uniqid();
    $file = UPLOAD_DIR.$id.'.png';
    $success = file_put_contents($file, $data);
}

function getChart($uniqid= null){
    if($uniqid){
        $this->layout = null;
        header("Content-type: image/png");
        header("Content-Disposition:attachment;filename='".$uniqid.".png'");
        readfile('../webroot/img/'.$uniqid.'.png');
        exit;
    } else exit;
}

function getChart ($uniqid = null) {

    if (!$uniqid) exit;

    $this->layout = null;

    if (headers_sent()) throw new Exception('Headers sent.');
    while (ob_get_level() && ob_end_clean());
    if (ob_get_level()) throw new Exception('Buffering is still active.');

    header("Content-type: image/png");
    header("Content-Disposition:attachment;filename='".$uniqid.".png'");
    readfile('../webroot/img/'.$uniqid.'.png');

    exit;
}

header("Content-length: $file_size")

header("Content-type: $file_type")

header("Content-Disposition: attachment; filename=$file_name");

// add ob_start() at the very top of your script
function getChart($uniqid= null){
    echo strlen(ob_get_clean()); die(); // if it's not 0 then you are definetly echoing something

    if($uniqid){
        $this->layout = null;
        header("Content-type: image/png");
        header("Content-Disposition:attachment;filename='".$uniqid.".png'");
        readfile('../webroot/img/'.$uniqid.'.png');
        exit;
    } else exit;
}

function getChart($uniqid= null){
    if($uniqid){

        $image = $uniqid;

        header("Cache-Control: public");
        header("Content-Description: File Transfer");
        header("Content-Disposition: attachment; filename=" . $image);
        header("Content-Type: image/jpg");
        header("Content-Transfer-Encoding: binary");

        readfile($image);

    } else exit;
}

getChart("060620121945.jpg");

function getChart($uniqid= null){
    if($uniqid){

        $mime_type = "image/png";
        $content = file_get_contents('../webroot/img/'.$uniqid.'.png');
        $base64   = base64_encode($content);
        return ('data:' . $mime_type . ';base64,' . $base64);

    } else exit;
}