angularjs directive will not call controller function

I have seen these issues before and it is usually because of parameters, etc, but I have a very simple example that I can't get to work....

I have a directive:

.directive('imageFileInput', function () {

    return {
        restrict: 'A',
        transclude: true,
        templateUrl: '/assets/tpl/directives/imageFileInput.html',
        scope: {
            onComplete: "&imageFileInput"
        },
        link: function (scope, element, attr) {

            // Get our input
            var input = element.find("input");

            // Function to handle the displaying of previews
            var preview = function () {

                // If we have an input
                if (input) {

                    // Create our file reader
                    var fileReader = new FileReader();

                    // Get our file
                    var file = input[0].files[0];

                    // Read the data from the file
                    fileReader.readAsDataURL(file);

                    // When the data has been read
                    fileReader.onload = function (e) {

                        // Apply the scope
                        scope.$apply(function () {

                            // And attach the result to our scope
                            scope.thumbnail = e.target.result;

                            // If we have a callback function
                            if (scope.onComplete) {

                                // Execute the function
                                scope.onComplete();
                            }
                        });
                    };
                }
            };

            // Bind a function to the onchange event
            input.bind('change', function () {

                // Create our preview
                preview();
            });
        }
    };
});

and the template looks like this:

<div class="thumbnail">
    <input type="file" accept="image/*" />
    <img src="{{ thumbnail }}" ng-if="thumbnail" />
    <div class="caption" ng-transclude>

    </div>
</div>

Pretty simple so far, it is just a directive that creates a nice preview for a file input. So the declaration of this directive is in my view like this:

<div id="{{ panel.id }}" image-file-input="controller.upload()">
    {{ panel.title }}
</div>

and in my controller, I have this function:

.controller('EditKitGraphicsController', ['GarmentService', 'garment', function (garments, garment) {
    var self = this;

    // Get our garment
    self.garment = garment;

    self.upload = function () {

        console.log('uploading');
    };
}])

So, if I break this down:

• My directive isolates the scope and expects a callback function called onComplete which is passed with the directive declaration (i.e. image-file-input="callback()")
• My directive calls this function after a scope.$apply and after checking the callback function exists, no parameters are passed
• My view passes the controller function upload() which again has no parameters
• My controller has a function attached to the scope called upload, which has a console.log in it
• Yet nothing gets executed...

Does anyone know why?