function Exif(){}
Exif.read=function(file,func){
	var reader=new FileReader();
	reader.onload=function(e){
		var mf=new MemoryFile(e.target.result,true);
		if(mf.readUInt16()!=0xFFD8) return func(false);	// no JPEG file
		var baseOffset=0;
		while(!mf.eof())
			if(mf.readUInt16()==0xFFE1 && mf.readUInt16()!=0 && mf.readUInt32()==0x45786966 && mf.readUInt16()==0){baseOffset=mf.tell();break;}	// find Exif header
		if(baseOffset==0) return func(false);
		mf.setByteOrderBig(mf.readUInt16()==0x4d4d);
		mf.skip(2);
		var ifd0=mf.readUInt32();
		var exif={};
		exif['IFD0']=Exif.readBlock(mf,baseOffset,ifd0);
		if(exif['IFD0'][34665]) exif['EXIF']=Exif.readBlock(mf,baseOffset,exif['IFD0'][34665]);
		if(exif['IFD0'][34853]) exif['GPS']=Exif.readBlock(mf,baseOffset,exif['IFD0'][34853]);
//console.log("EXIF: "+JSON.stringify(exif));
		func(exif);
	};
	reader.readAsArrayBuffer(file.slice(0,64*1024));
};
Exif.readBlock=function(mf,baseOffset,offset){
	var tags={},numerator,denominator;
	mf.seek(baseOffset+offset);
	var num=mf.readUInt16();
//console.log("tag num "+num);
	for(var a=0;a<num;a++){
		var id=mf.readUInt16();
		var format=mf.readUInt16();
		var count=mf.readUInt32(),length;
		switch(format){
			case 1:length=1;break;	// unsigned byte
			case 2:length=count;count=1;break;	// ASCII string
			case 3:length=2;break;	// unsigned short
			case 4:length=4;break;	// unsigned long
			case 5:length=8;break;	// unsigned rational
			case 6:length=1;break;	// signed byte
			case 7:length=1;break;	// undefined
			case 8:length=2;break;	// signed short
			case 9:length=4;break;	// signed long
			case 10:length=8;break;	// signed rational
			case 11:length=4;	break;// single float
			case 12:length=8;	break;// double float
		}
		var mf2;
		if(length*count>4){	// is offset
			mf2=new MemoryFile(mf.toArrayBuffer(baseOffset+mf.readUInt32(),length*count),mf.getByteOrderBig());
		}else{	// is value
			mf2=new MemoryFile(mf.toArrayBuffer(mf.tell(),4),mf.getByteOrderBig());
			mf.skip(4);
		}
//console.log("tag id="+id+" format="+format+" length="+length+" count="+count+" mf.size="+mf2.size);
		var values=[];
		for(var b=0;b<count;b++){
			switch(format){
				case 1:values.push(mf2.readByte());break;
				case 2:values.push(mf2.readCharsASCII(length).replace('\0','').trim());break;
				case 3:values.push(mf2.readUInt16());break;
				case 4:values.push(mf2.readUInt32());break;
				case 5:numerator=mf2.readUInt32();denominator=mf2.readUInt32();values.push(numerator/denominator);break;	// unsigned rational
				case 6:values.push(mf2.readSByte());break;
				case 7:values.push(mf2.readByte());break;	// undefined
				case 8:values.push(mf2.readInt16());break;
				case 9:values.push(mf2.readInt32());break;
				case 10:numerator=mf2.readInt32();denominator=mf2.readInt32();values.push(numerator/denominator);break;	// signed rational
				case 11:values.push(mf2.readFloat());break;
				case 12:values.push(mf2.readDouble());break;
			}
		}
		if(count==1) tags[id]=values[0];else tags[id]=values;
	}
	return tags;
};