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相片中記載許多拍攝當時的資訊，那我們該如何去擷取相片資訊呢？如解析度、拍攝時間、拍攝地點、光圈、快門、品牌、機種等等。

首先在專案加入AssetsLibrary.framework，並在.m中#import <AssetsLibrary/AssetsLibrary.h>。

-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
    DLog(@"info:%@",info);
}

info列印出來會像這樣：

info:{     UIImagePickerControllerMediaType = “public.image";     UIImagePickerControllerOriginalImage = “<UIImage: 0x17e49ef0>";     UIImagePickerControllerReferenceURL = “assets-library://asset/asset.JPG?id=1C151E38-D4DD-444A-996C-9651803E508E&ext=JPG"; }

此時要使用ALAssetsLibrary追溯UIImagePickerControllerReferenceURL這個key，asset.defaultRepresentation.metadata即可取得相片資訊，。

    ALAssetsLibrary *assetLibray = [[ALAssetsLibrary alloc] init];
    [assetLibray assetForURL:[info objectForKey:@"UIImagePickerControllerReferenceURL"] resultBlock:^(ALAsset *asset){
        DLog(@"metadata:%@",asset.defaultRepresentation.metadata);
    } failureBlock:^(NSError *err){
        DLog(@"err:%@",err);
    }];

列印出來會像這樣：

metadata:{

    ColorModel = RGB;

    DPIHeight = 72;

    DPIWidth = 72;

    Depth = 8;

    PixelHeight = 2048;

    PixelWidth = 1536;

    “{Exif}" =     {

        ApertureValue = “2.52606882168926″;

        BrightnessValue = “3.007532956685499″;

        ColorSpace = 1;

        ComponentsConfiguration =         (

            1,

            2,

            3,

            0

        );

        DateTimeDigitized = “2013:08:09 15:49:37″;

        DateTimeOriginal = “2013:08:09 15:49:37″;

        ExifVersion =         (

            2,

            2,

            1

        );

        ExposureMode = 0;

        ExposureProgram = 2;

        ExposureTime = “0.04166666666666666″;

        FNumber = “2.4″;

        Flash = 16;

        FlashPixVersion =         (

            1,

            0

        );

        FocalLenIn35mmFilm = 35;

        FocalLength = “4.28″;

        ISOSpeedRatings =         (

            50

        );

        LensMake = Apple;

        LensModel = “iPhone 4S back camera 4.28mm f/2.4″;

        LensSpecification =         (

            “4.28″,

            “4.28″,

            “2.4″,

            “2.4″

        );

        MeteringMode = 5;

        PixelXDimension = 3264;

        PixelYDimension = 2448;

        SceneCaptureType = 0;

        SceneType = 1;

        SensingMethod = 2;

        ShutterSpeedValue = “4.584985835694051″;

        SubjectArea =         (

            1631,

            1223,

            881,

            881

        );

        SubsecTimeDigitized = 023;

        SubsecTimeOriginal = 023;

        WhiteBalance = 0;

    };

    “{GPS}" =     {

        Altitude = “34.84348395546824″;

        AltitudeRef = 0;

        DateStamp = “2013:08:09″;

        Latitude = “25.01262221666667″;

        LatitudeRef = N;

        Longitude = “121.5152283333333″;

        LongitudeRef = E;

        TimeStamp = “07:49:34″;

    };

    “{MakerApple}" =     {

        1 = 0;

        3 =         {

            epoch = 0;

            flags = 1;

            timescale = 1000000000;

            value = 51254606438541;

        };

        4 = 1;

        5 = 128;

        6 = 126;

        7 = 0;

    };

    “{TIFF}" =     {

        DateTime = “2013:08:09 15:49:37″;

        Make = Apple;

        Model = “iPhone 4S";

        ResolutionUnit = 2;

        Software = “7.0″;

        XResolution = 72;

        YResolution = 72;

    };

}

得到的相片資訊相當多，可以有許多方向使用。

參考：使用 AssetsLibrary 取得圖庫中檔案的相關資訊、how to get the data from UIImagePickerControllerReferenceURL iOS Sdk。