images in gnome canvas

Hi,

I am trying to load an image and then manipulate it with the use of the gnome canvas but unfortunately i've found it is making my entire program quite unresponsive and slow.

I load the pixbuf form a file and then draw it on the canvas in the main loop;

map = gdk_pixbuf_new_from_file_at_size ("../pixmaps/map_brisbane.png", 900, 900, NULL);
canvMap = gnome_canvas_item_new(gnome_canvas_root(gnomecanvas),
                             GNOME_TYPE_CANVAS_PIXBUF,
                                "anchor",GTK_ANCHOR_CENTER,
                                "height-in-pixels",0,
                                "width-in-pixels",0,
                                "x-in-pixels",0,
                                "y-in-pixels",0,
                                "pixbuf",map,
                                "x", (double)300,
                                "y", (double)300,
                                "height",(double)600,
                                "width", (double)600,  
                                NULL);

I use an idle_callback function to move the image around and i simply change the pixels per unit to zoom the entire canvas;

        double xvel; //x velocity
        double yvel; //y velocity
        double vel= gtk_range_get_value(lookup_widget(GTK_WIDGET(app1), "hscale1"));

        xvel = vel*sin(home_head*C_DEG2RAD);
        yvel = vel*cos(home_head*C_DEG2RAD);
        gnome_canvas_item_move(canvMap,xvel/20,yvel/20);

The problem I am having is when the image is enlarged, when I decrease the size it seems to function normaly again. Also, without the image the program functions normally so i'm gussing it has something to do with rendering the pixbuf to the canvas but i'm not too sure what explicitly would be causing this problem weather it'd be the image itself or an inherent problem with the gnome canvas or simply me doing something completely wrong. any help would be greatly appreciated.

Thanks,

Chris