I found this handy little class in a Flash project that I just had to jump back into. It's an easy way to take a bitmap snapshot of any DisplayObject, then resize the image data to fit another frame. You can fill the area, letterbox/pillowbox, or just scale to new dimensions. Feel free to use this, and nevermind the warnings that show up in FDT :)

package com.cache.util
{
import flash.display.BitmapData;
import flash.display.DisplayObject;
import flash.geom.Matrix;
import flash.geom.Point;
import flash.geom.Rectangle;
/**
* @author justin - http://uihacker.blogspot.com/
*/
public class ImageEdit
{
/**
* Return a snapshot of a DisplayObject
*/
public static function getBitmapData( vSource:DisplayObject, vW:Number=NaN, vH:Number=NaN, vTransparent:Boolean=true, vColor:int=0xFF00FF, vMatrix:Matrix=null ):BitmapData
{
// set defaults.
var vWidth:int = ( isNaN( vW )) ? vSource.width : vW;
var vHeight:int = ( isNaN( vH )) ? vSource.height : vH;
// create BitmapData object.
var vBmp:BitmapData = new BitmapData( vWidth, vHeight, vTransparent, vColor );
// draw contents of source clip into target.
if ( vMatrix == null ) vBmp.draw( vSource, null, null, null, null, true );
else vBmp.draw( vSource, vMatrix, null, null, null, true );
return vBmp;
}
/**
* Build & return a matrix to use to scale a bitmap
*/
public static function getScaleMatrix( scale:Number ) : Matrix
{
var matrix:Matrix = new Matrix();
matrix.scale(scale, scale);
return matrix;
}
/**
* Pass these constants into the getResizedBitmapData() function
*/
public static const RESIZE_SCALE:String = 'ImageEdit.resizeScale';
public static const RESIZE_LETTERBOX:String = 'ImageEdit.resizeLetterbox';
public static const RESIZE_CROP:String = 'ImageEdit.resizeCrop';
/**
* Return a resized BitmapData copy of the original
*/
public static function getResizedBitmapData( sourceBitmap:BitmapData, targetWidth:Number, targetHeight:Number, resizingMethod:String = '', disposeSourceBmp:Boolean = true ) : BitmapData
{
// get current dimensions
var curW:Number = sourceBitmap.width;
var curH:Number = sourceBitmap.height;
// get ratios of 2 sides
var ratio_w:Number = targetWidth / curW;
var ratio_h:Number = targetHeight / curH;
var shorterRatio:Number = ( ratio_w > ratio_h ) ? ratio_h : ratio_w;
var longerRatio:Number = ( ratio_w > ratio_h ) ? ratio_w : ratio_h;
// apply sizing
switch( resizingMethod )
{
case RESIZE_CROP :
// get shorter ratio, so we fill the target area
var resizedWidth:int = Math.round( curW * longerRatio );
var resizedHeight:int = Math.round( curH * longerRatio );
// create copy of, and resize the source bitmap
var resizedSourceBmp:BitmapData = new BitmapData( resizedWidth, resizedHeight, false, 0x00000000 );
// create scale matrix
var matrix:Matrix = new Matrix();
matrix.scale( longerRatio, longerRatio );
// take resized snapshot
resizedSourceBmp.draw( sourceBitmap, matrix );
// draw into destination bitmap, letterbox/pillowbox style
var destBitmap:BitmapData = new BitmapData( targetWidth, targetHeight, false, 0x00000000 );
var offset:Point = new Point( targetWidth / 2 - resizedWidth / 2, targetHeight / 2 - resizedHeight / 2 );
destBitmap.copyPixels( resizedSourceBmp, new Rectangle( -offset.x, -offset.y, resizedSourceBmp.width, resizedSourceBmp.height ), new Point() );
// clean up temp BitmapData
resizedSourceBmp.dispose();
if( disposeSourceBmp ) sourceBitmap.dispose();
return destBitmap;
break;
case RESIZE_LETTERBOX :
// get shorter ratio, so we fill the target area
var resizedWidth:int = Math.round( curW * shorterRatio );
var resizedHeight:int = Math.round( curH * shorterRatio );
// create copy of, and resize the source bitmap
var resizedSourceBmp:BitmapData = new BitmapData( resizedWidth, resizedHeight, false, 0x00000000 );
// create scale matrix
var matrix:Matrix = new Matrix();
matrix.scale( shorterRatio, shorterRatio );
// take resized snapshot
resizedSourceBmp.draw( sourceBitmap, matrix );
// draw into destination bitmap, letterbox/pillowbox style
var destBitmap:BitmapData = new BitmapData( targetWidth, targetHeight, false, 0x00000000 );
var pastePoint:Point = new Point( targetWidth / 2 - resizedWidth / 2, targetHeight / 2 - resizedHeight / 2 );
destBitmap.copyPixels( resizedSourceBmp, new Rectangle( 0, 0, resizedSourceBmp.width, resizedSourceBmp.height ), pastePoint );
// clean up temp BitmapData
resizedSourceBmp.dispose();
if( disposeSourceBmp ) sourceBitmap.dispose();
return destBitmap;
break;
case RESIZE_SCALE :
default :
// create output bitmap
var vBmp:BitmapData = new BitmapData( targetWidth, targetHeight, false, 0x00000000 );
// create scale matrix
var matrix:Matrix = new Matrix();
matrix.scale( ratio_w, ratio_h );
// snapshot with scale & return
vBmp.draw( sourceBitmap, matrix );
// clean up temp BitmapData
if( disposeSourceBmp ) sourceBitmap.dispose();
return vBmp;
break;
}
return null;
}
}
}