resize image on the fly - php

Question

I've built a gallery using ci where the image that is uploaded is kept its same size as long as its within 3000x5000 px range. Upon displaying them and since i haven't cropped thumbnails , how can I re size them when needed so say i want to re-size a list of them as 150x150 how would i go about this?
i followed the guide
http://ellislab.com/codeigniter/user-guide/libraries/image_lib.html
Problem is when loading the library it wants me to specify each images complete config information.
So say I loaded the variable into a controller to be displayed in a view, and when loading it would look like this:
foreach($gallery as $img)
{
echo "<div>";
echo "<img src='" . $this->img_lib->resize($img->imagepath, 150, 150) . "'>";
echo "</div>";
}
ps: does the image gets saved when its resized? because i dont want that.
better solution: http://www.matmoo.com/digital-dribble/codeigniter/image_moo/

Answer 1

I know how to do it outside of ci. Essentially the img "src" needs to equal a php script OR be intercepted by htaccess which then redirects it to a php script.
You could try something like this:
foreach($gallery as $img)
{
echo "<div>";
echo "<img src='/imageResize.php?path=" . $img->imagepath . "'>";
echo "</div>";
}
File: imageResize.php
$path = $_REQUEST['path'];
$this->img_lib->resize($path, 150, 150);
Depending on the folder structure of your site it would be better to just pass the filename rather than the full path. Even better is to use .htaccess (which I do in our CMS) to intercept the image and resize/crop on the fly. e.g. <img src="/path/to/image.jpg?w=150&h=150" />
Does that help provide some direction?
On your other question, a physical file isn't saved on the server unless you specify it to do so.

Answer 2

The answer from #SaRiD is on the right track. However, it doesn't necessarily have to be outside of CI. You can point the image source to a controller method that takes care of the resizing and serve the image.
You also need to use the correct headers to identify the image resource to the browser, within this method.
You state that you do not want to save the thumbnail. This obviously depend on the need of the application. You can set it in a way that it serves the previously cropped and saved thumbnails to the browser if that exists (from a previous request), rather than creating and serving thumbnails each time - it will save you some CPU cycles.