Why am I getting a "Call to a member function on a non-object" error?

I'm working with the Zend framework, backed by MySQL, and trying to set up an index view. However, with the code I have, I keep getting the "call to a member function on a non-object" error and I don't know how to solve it. Here's the Controller for my index page:

 public function indexAction() {
     $dImage = new Application_Model_DImage();
 }

Here's the code for the DImage model that it references:

public function getImageDesCol ($Id) {
    return $this->getDb()->fetchCol("SELECT description FROM d_image WHERE d_id = ?", $Id);
}

Finally, here's the source of my Index view page where I'm trying to display the values from the DImage model:

  <?php $description = $this->dImage->getImageDesCol($id) ?>
  <label><?php echo $description[0] ?></label>

When I load that page, I get the "Call to a member function getImageDesCol() on a non-object" error instead of a rendered page. Since I'm new to the Zend framework and PHP in general, I feel like there's something obvious that I'm missing. What can I do to fix this?

Change:

 public function indexAction()
 {
     $dImage = new Application_Model_DImage();
 }

To:

 public function indexAction()
 {
     $this->dImage = new Application_Model_DImage();
 }

You must add the Application_Model_DImage object to the view, or else the view does not know of an object with that name. Do this:

public function indexAction()
{
    $dImage = new Application_Model_DImage();
    $this->view->dImage = $dImage;
}

Then you will have your $dImage available to your view scripts.

Your view scripts execute in the context of a Zend_View object, but you were creating your Application_Model_DImage object in the context of your controller (an instance of Zend_Controller_Action). As such, you need to explicitly pass to the view whatever objects the view scripts will use. By default, Zend_Controller_Action has a view object ready for you (check here).