it not work with png created a thumb png but haven't data , like null data :D with jpg , jpeg still working without error why ?

function thumbnail($pathtoFile,$thumWidth,$pathtoThumb) {

    //infor of image
    $infor = pathinfo($pathtoFile);

    // Setting the resize parameters 
    list($width, $height) = getimagesize($pathtoFile); 

    $modwidth = $thumWidth; 
    $modheight = floor( $height * ( $modwidth / $width )); 


    // Resizing the Image 
    $thumb = imagecreatetruecolor($modwidth, $modheight);

    switch(strtolower($infor['extension'])) {
        case 'jpeg':
        case 'jpg':
            $image = imagecreatefromjpeg($pathtoFile); 
            break;

        case 'gif':
            $image = imagecreatefromgif($pathtoFile); 
            break;

        case 'png':
            $image = imagecreatefrompng($pathtoFile); 
            break;
    }

    imagecopyresampled($thumb, $image, 0, 0, 0, 0, $modwidth,
            $modheight, $width, $height);

    switch(strtolower($infor['extension'])) {
        case 'jpeg':
        case 'jpg':
            imagejpeg($thumb,$pathtoThumb, 70); 
            break;
        case 'gif':
            imagegif($thumb,$pathtoThumb, 70); 
            break;
        case 'png':

            imagepng($thumb,$pathtoThumb, 70); 
            break;
    }

    //destroy tmp
    imagedestroy($thumb);
}