How can I use getjson to parse a php output?

How can I use getjson to parse a php output?

I am totally lost when it come to json/ajax stuff (I guess I am just too old).

I have a php file (preload.php) which reads:

<?php

/* Read all files from directory */
$ImageDirectory = ($_GET['directory']);
$ImageDirectory = dir($ImageDirectory);
$ImageArray = array();

/* Store imagefiles in an array */
while($ImageLoop = $ImageDirectory->read())
{
   if (isImage($ImageLoop)) {
        $ImageArray[] = $ImageLoop;
    }
}

/* Is the file an image? */
function isImage($FileLoop) {
    return preg_match('/^.+\.(gif|png|jpe?g|bmp|tif)$/i', $FileLoop);
}

/* Return the array contents */
echo $ImageArray;
?>


And a Javascript function:

function PreLoadImages(ImageDir) {
   for(var counter = 0; counter<ImageDir.length; counter++) {
      ImageObject = new Image();
      ImageObject.src = ImageDir[counter];
   }
}


This JS is in an external (.js) file. Obviously I want the argument ImageDir to be read from the php file. I suspect I have to use $.getjson, but am too stupid to know how.

Any help would be much appreciated.