使用PHImageManager进行图像提取不提供完整的元数据

Question

我正在使用requestImageDataForAsset来获取图像的完整数据，然后使用ImageIO来提取其exif信息。但是，似乎我没有获得图像的完整元数据，这里有没有人有类似的问题？

这是我的代码

//Code to fetch PhotoAsset
... 
        PHImageManager.defaultManager().requestImageDataForAsset(self.selectedPhotoAsset, options: options) {
            photoData, photoUTI, photoOrientation, photoInfo in
            self.selectedPhotoData = photoData

            self.fetchPhotoMetadata()

        }
    func fetchPhotoMetadata() {
        let selectedImageSourceRef = CGImageSourceCreateWithData(self.selectedPhotoData as CFData, nil) as CGImageSourceRef
        let imagePropertiesDictionary = CGImageSourceCopyPropertiesAtIndex(selectedImageSourceRef, 0, nil) as NSDictionary

        for (key, value) in imagePropertiesDictionary {
            println("Key: \(key) Value: \(value)")
        }
    }

元数据的输出：

Key: {TIFF} Value: {
    ResolutionUnit = 2;
    XResolution = 72;
    YResolution = 72;
}
Key: DPIWidth Value: 72
Key: DPIHeight Value: 72
Key: ColorModel Value: RGB
Key: PixelHeight Value: 768
Key: Depth Value: 8
Key: {Exif} Value: {
    ColorSpace = 1;
    ComponentsConfiguration =     (
        1,
        2,
        3,
        0
    );
    ExifVersion =     (
        2,
        2,
        1
    );
    FlashPixVersion =     (
        1,
        0
    );
    PixelXDimension = 1024;
    PixelYDimension = 768;
    SceneCaptureType = 0;
}
Key: PixelWidth Value: 1024