<mx :Script>
        < ![CDATA[
 
                // Maximum  width
                private var mxw:Number = 500;              
                // Maximum height
               private var mxh:Number = 250;
 
               public function onImageComplete(e:Event):void
               {
                var wthMaxRatio:Number = mxw / mxh;
 
                // no resize needed
                if (e.target.contentWidth <= mxw && e.target.contentHeight <= mxh)
                {
                    e.target.x = (mxw - e.target.contentWidth) / 2;
                    e.target.y = (mxh - e.target.contentHeight) / 2;
                }
                else
                {
                    var wthImgRatio:Number = e.target.contentWidth / e.target.contentHeight;
 
                    if (wthImgRatio > wthMaxRatio)
                    {
                        // will max out the width
                        e.target.width = mxw;
                        var imgHeight:Number = Math.round( (mxw / e.target.contentWidth) * e.target.contentHeight );
                        var newY:Number = Math.round( (mxh - imgHeight) / 2 );
                        e.target.x = 0;
                        e.target.y = newY;
                    }
                    else
                    {
                        // will max out the height
                        e.target.height = mxh;
                        var imgWidth:Number = Math.round( (mxh / e.target.contentHeight) * e.target.contentWidth );
                        var newX:Number = Math.round( (mxw - imgWidth) / 2 );
                        e.target.x = newX;
                        e.target.y = 0;
                    }
                }
              }
         ]]>
    </mx>
 
 
      <mx :Canvas width="500" height="250"
            verticalScrollPolicy="off" horizontalScrollPolicy="off" 
            backgroundColor="#000000">
 
            <mx :Image id="theimage"
                maintainAspectRatio="true"
		scaleContent="true"
                complete="onImageComplete(event)" />
 
        </mx>