problemi con imagecopyresized

[cecco-idro]

Salve, uso questa funzione da diverso tempo ma questa volta devo fare una copia ridotta e dalle dimensioni fisse e non ci riesco.

$thumbWidth = 463;
$thumbHeight = 276;
//resyzer 
$tnsize_x = (integer) $thumbWidth; //276
$tnsize_y = (integer) $thumbHeight; //276
$sz = getimagesize("$imageDirectory/$imageName");
$x = $sz[0];    // big image width 
$y = $sz[1];    // big image height
$w = $tnsize_x;
$h = $tnsize_y;
if (($x/$y)>($w/$h)){ 
    $cx = ($x-($h*$w/$y))/2; 
    $cw = 0; 
    $ch = 0;     
    $cy = 0;         
} else { 
    $cx = 0; 
    $cw = 0;     
    $ch = 0;     
    $cy = ($y - ($h*$x/$w))/0; 
}
//crea la miniatura e la salva
$srcImg = imagecreatefromjpeg("$imageDirectory/$imageName");
$thumbImg = imagecreatetruecolor($thumbWidth, $thumbHeight);
imagecopyresized($thumbImg, $srcImg, $cw, $ch, $cx, $cy, $w, $h, $x, $y);