Quickie: Adding the ability to set a maximum height?

[djfox]

I have this following code:

 

<?php
// File and new size
//$imgfile = 'thumb.jpg';
//$percent = 0.2;
header('Content-type: image/jpeg');
$imgfile = $_GET['img'];
list($width, $height) = getimagesize($imgfile);
//echo $width, $height;
$newwidth = 100;
$factor = $newwidth / $width;
//echo $factor;
$newheight = $height * $factor;

$thumb = ImageCreateTrueColor($newwidth,$newheight);
$source = imagecreatefromjpeg($imgfile);

imagecopyresized($thumb, $source, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);

imagejpeg($thumb);
?>

 

It has the width set to 100 pixels. How can I add in for this code to set the height to 100? I don`t want it coming out 100x100 pixels. What I`m looking for is for this to set the image pixels as maximum 100 pixels wide and maximum 100 pixels high. So if the image is shorter in either field, the thumbnail wil adjust accordingly.