omdøbe billede ved upload

jeg benytter pt nedenstående script til upload af billede, som jeg gerne vil omdøbe til eks. $tableid.gif

Format: de må bruge Jpg, jpeg, gif

Form input:
<input type="file" name="image_file" size="20">


upload billede script:

if($_POST["action"] == "submit")
{
unset($imagename);

if(!isset($_FILES) && isset($HTTP_POST_FILES))
$_FILES = $HTTP_POST_FILES;

if(!isset($_FILES['image_file']))
$error["image_file"] = "An image was not found.";


$imagename = basename($_FILES['image_file']['name']);
//echo $imagename;

if(empty($imagename))
$error["imagename"] = "The name of the image was not found.";

if(empty($error))
{
$newimage = "idpicture/" . $imagename;
//echo $newimage;
$result = @move_uploaded_file($_FILES['image_file']['tmp_name'], $newimage);
if(empty($result))
$error["result"] = "There was an error moving the uploaded file.";
}

}