take the centre of the large image to create the small image.
The scripts I've written for generating thumbnails are designed to have a maximum height and width of 100x100. It then finds which is the large dimension and shrinks the other proportionally.
A 1000x500px image would become 100x50, and so forth.
Additionally, if both dimensions are under 100x100, then it simply leaves as is, for a smaller image, such as a logo, rather than stretching it.
It would be possible to take the center, but this isn't a great representation of the full image. It would also lead to pixelated previews for small images (unless you're sure you wont have any).
Here's a script that will do what I posted above. If you need it to do something else, ask, and I'll see what can be done.
<?php
//thumbnail.php
//use this script as any image
//ex: <img src="thumbnail.php?img=trees.jpg">
//Note that you can use any path you'd like, but I would recommend
//adding something to the script to disallow remote images.
//This way, no one just uses your script.
//Adding another directory to the path within the script will solve this:
//$path = 'images/'.$img;
//There should be no real need to modify any of this
//but I have marked several areas that can have custom values
include('bmp.php');
//BMP functions -- SEE NOTE
// The file
$img = isset($_GET['img'])?$_GET['img']:'';
if ($img == '') die('Image Does Not Exist');
//You could enable a default image with the error message
//so the error displayed in a page as an image (rather than
//an X for image not loaded).
//instead of die(), use $img = 'error.jpg';
//as described above, this prevents custom locations of images
//so no one can use your script from another page
$dir = 'images/';
//change as you want
$filename = $dir.urldecode($_GET['img']);
function getimagetype($img) {
$size = getimagesize($img);
$mime = $size['mime'];
$type = substr($mime,strpos($mime,'/')+1);
if (in_array($type, array('gif', 'png', 'bmp'))) {
return $type;
}
else if ($type == 'jpeg') {
return 'jpg';
}
else {
return FALSE;
}
}
if (getimagetype($filename)) {
$ext = getimagetype($filename);
$imageextok = 1;
}
$extn=0;
foreach (array("jpg","gif","png","bmp") as $imageext) {
$extn++;
if ($ext == $imageext) { break; }
}
if($imageextok != 1) { die('Image Filetype Incorrect - '.$filename); }
// Set a maximum height and width
$width = 100;
$height = 100;
// Make image
if ($extn == 1) {
if (@imagecreatefromjpeg($filename)) $image = imagecreatefromjpeg($filename);
}
else if ($extn == 2) {
if (@imagecreatefromgif($filename)) $image = imagecreatefromgif($filename);
}
else if ($extn == 3) {
if (@imagecreatefrompng($filename)) $image = imagecreatefrompng($filename);
}
else if ($extn == 4) {
if (@imagecreatefrombmp($filename)) $image = imagecreatefrombmp($filename);
}
if (!isset($image)) die('Image Filetype Incorrect.');
// Get new dimensions
$width_orig = imagesx($image);
$height_orig = imagesy($image);
//override w/h with smaller values if image is under 100x100 for w&h
if ($width_orig<$width && $height_orig<$height) {
$height = $height_orig;
$width = $width_orig;
}
else {
$ratio_orig = $width_orig/$height_orig;
if ($width/$height > $ratio_orig) {
$width = $height*$ratio_orig;
} else {
$height = $width/$ratio_orig;
}
}
// Resample
$image_p = imagecreatetruecolor($width, $height);
imagecopyresampled($image_p, $image, 0, 0, 0, 0, $width, $height, $width_orig, $height_orig);
// Content type
header('Content-type: image/gif');
// Output
imagegif($image_p, null, 30);
////FORMAT OPTIONS:
////replace 'gif' in the last two lines with 'png' or 'jpeg' if desired.
////for jpg, quality (30 above) is needed; for png, remove 3rd parameter
////bmp would also work if you have bmp.php included, but not good for
////thumbnails, due to size.
?>
Note: to use this you must have PHP installed/enabled on your server.
For BMP images to work, you must include the bmp.php script. That can be found here (and by a google search for 'imagecreatefrombmp'): http://www.hotscripts.com/Detailed/41077.html
Also, this script is a bit slow, but that's just how it works generating thumbnails from huge images, at least with the PHP GD library.