用ImageInfoExtractor类在图片未加载时获取图片信息

ImageInfoExtractor类通过ByteArray方式获取jpg,png,gif等图片的相关信息：例如图片大小，图片宽和高，图片格式等。当然，这一切都是未加载图片之前，也就是说如果一张相当大的图片，你不必完全加载后才得到这些信息，用ImageInfoExtractor类可以马上就能读取到它了。
使用方法很简单：

var myExtractor:ImageInfoExtractor = new ImageInfoExtractor();
myExtractor.addEventListener(ImageInfoExtractor.PARSE_COMPLETE, infoHandler);
myExtractor.addEventListener(ImageInfoExtractor.PARSE_FAILED, errorHandler);
myExtractor.file = "http://www2.pc1280.com/images3/wall/20051104/1280_3d_1015.jpg";

var t1:Number=getTimer();
var infoTxt:TextField=new TextField();
infoTxt.width=200;
infoTxt.height=200;
addChild(infoTxt);

function infoHandler(e:Event):void {
trace(getTimer()-t1);
var line0:String = "image size = " + myExtractor.size;
var line1:String = "pixel width = " + myExtractor.width;
var line2:String = "pixel height = " + myExtractor.height;
var line3:String = "bit depth = " + myExtractor.bitsPerPixel;
var line4:String = "file type = " + myExtractor.fileType;
var line5:String = "mime type = " + myExtractor.mimeType;
infoTxt.htmlText = line0 +"\n"+ line1 +"\n"+ line2 +"\n"+ line3 +"\n"+ line4 +"\n"+ line5;
}

function errorHandler(e:Event):void {
trace( "Size could not be obtained, file was not according to JFIF specification" );
}