iOS开发中用imageIO渐进加载图片及获取exif的方法

    DPIWidth = 72;
    Depth = 8;
    Orientation = 6;
    PixelHeight = 2448;
    PixelWidth = 3264;
    "{Exif}" =     {
        ApertureValue = "2.526069";
        BrightnessValue = "-0.5140446";
        ColorSpace = 1;
        ComponentsConfiguration =         (
            1,
            2,
            3,
            0
        );
        DateTimeDigitized = "2013:06:24 22:11:30";
        DateTimeOriginal = "2013:06:24 22:11:30";
        ExifVersion =         (
            2,
            2,
            1
        );
        ExposureMode = 0;
        ExposureProgram = 2;
        ExposureTime = "0.06666667";
        FNumber = "2.4";
        Flash = 16;
        FlashPixVersion =         (
            1,
            0
        );
        FocalLenIn35mmFilm = 33;
        FocalLength = "4.13";
        ISOSpeedRatings =         (
            400
        );
        MeteringMode = 3;
        PixelXDimension = 3264;
        PixelYDimension = 2448;
        SceneCaptureType = 0;
        SensingMethod = 2;