javascript programming: how to remove blank area of a tile map in openlayers

I use a open source tool named "maptiler" to create a tile map on a raster impage (no geo-info). It also create a HTML file which uses openlayers lib to display the created tile map. It looks fine except the map (image) is draggable and there are a large blank area in the screen which looks urgly. Do you know how to remove the blank area around the map?

Thanks for your help!

screenshot is here: use http to visit: "218.244.136.35:8080/7777/a.png"

My software is like this:

var options = {
              controls: [
                        new OpenLayers.Control.Attribution(),
                        new OpenLayers.Control.TouchNavigation({
                            dragPanOptions: {
                                enableKinetic: true
                            }
                        }),
                        new OpenLayers.Control.LayerSwitcher(),
                        new OpenLayers.Control.Zoom()
                ],
                maxExtent: new OpenLayers.Bounds(  0.0, -3448.0, 2426.0, 0.0 ),
                maxResolution: 16.000000,
                numZoomLevels: 5
            };


var layer = new OpenLayers.Layer.TMS( "TMS Layer","",
       {  url: '', serviceVersion: '.', layername: '.', alpha: true,
                                type: 'png', getURL: overlay_getTileURL 
                    });

map = new OpenLayers.Map('map', options);                       
map.addLayer(layer);
var mapBounds = new OpenLayers.Bounds( 0.0, -3448.0, 2426.0, 0.0); // this is the resolution of my image
map.zoomToExtent( mapBounds );          
map.addControl(new OpenLayers.Control.MousePosition());

You must add restrictedExtent: to the options of the map. An example of this feature is visible at:

http://openlayers.org/dev/examples/restricted-extent.html

If you had used new MapTiler (from http://www.maptiler.com) to generate the tiles, then the javascript code would be cleaner and you would also get Leaflet viewer out of the box and minimized tiles.