Save the exif metadata using the new PHPhotoLibrary

Question

I am currently using AVCaptureStillImageOutput to get a full resolution picture. I am also able to get the exif metadata using the following code:

[self.stillImageOutput captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler: ^(CMSampleBufferRef imageSampleBuffer, NSError *error)
     { 

         CFDictionaryRef metaDict = CMCopyDictionaryOfAttachments(NULL, imageSampleBuffer, kCMAttachmentMode_ShouldPropagate);
         CFMutableDictionaryRef mutableDict = CFDictionaryCreateMutableCopy(NULL, 0, metaDict);

         NSLog(@"test attachments %@", mutableDict);

         // set the dictionary back to the buffer
         CMSetAttachments(imageSampleBuffer, mutableDict, kCMAttachmentMode_ShouldPropagate);

         NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer];

         UIImage *image = [[UIImage alloc] initWithData:imageData];    
         [self.delegate frameReadyToSave:image withExifAttachments: mutableDict];
     }];

The metadata being located in the mutableDict variable. Now, I want to save this picture in two different places, with the metadata. I want to save it on the disk in the application folders and in the Photo Library.

Now, I tried to save the image, in another method, using the following (the image variable you see is a custom object):

NSData* imageData = UIImageJPEGRepresentation(image.image, 1.0f);

[imageData writeToFile:image.filePath atomically:YES];

UIImageWriteToSavedPhotosAlbum(image.image, nil, nil, nil);

Now, the image is properly saved but does not contain any Exif metadata.

From what I have read, I need to use the PHPhotoLibrary to do so but the documentation isn't too loquacious on that. Here's what I found:

[[PHPhotoLibrary sharedPhotoLibrary] performChanges:^{
    PHAssetChangeRequest *createAssetRequest = [PHAssetChangeRequest creationRequestForAssetFromImage:image.image];      

} completionHandler:nil];

But how do I save the metadata with it?

Answer 1

I would suggest you use ImageIO to accomplish that:

-(void)frameReadyToSave:(UIImage*)image withExifAttachments:(NSMutableDictionary*)mutableDict
{
    NSData* imageData = UIImageJPEGRepresentation(image, 1.0f);
    CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef) imageData, NULL);
    __block NSURL* tmpURL = [NSURL fileURLWithPath:@"example.jpg"]; //modify to your needs
    CGImageDestinationRef destination = CGImageDestinationCreateWithURL((__bridge CFURLRef) tmpURL, kUTTypeJPEG, 1, NULL);
    CGImageDestinationAddImageFromSource(destination, source, 0, (__bridge CFDictionaryRef) mutableDict);
    CGImageDestinationFinalize(destination);
    CFRelease(source);
    CFRelease(destination);
    [[PHPhotoLibrary sharedPhotoLibrary] performChanges:^{
        [PHAssetChangeRequest creationRequestForAssetFromImageAtFileURL:tmpURL];
    }   completionHandler:^(BOOL success, NSError *error) {
        //cleanup the tmp file after import, if needed
    }];
}

Answer 2

Use this to merge metadata into image data and save it to Photo Library:

func saveImageData(data: Data, metadata: NSDictionary? = nil, album: PHAssetCollection, completion:((PHAsset?)->())? = nil) {
    var placeholder: PHObjectPlaceholder?

    PHPhotoLibrary.shared().performChanges({
        var changeRequest: PHAssetChangeRequest

        if let metadata = metadata {
            let newImageData = UIImage.mergeImageData(imageData: data, with: metadata)
            changeRequest = PHAssetCreationRequest.forAsset()
            (changeRequest as! PHAssetCreationRequest).addResource(with: .photo, data: newImageData as Data, options: nil)
        }
        else {
            changeRequest = PHAssetChangeRequest.creationRequestForAsset(from: UIImage(data: data)!)
        }

        guard let albumChangeRequest = PHAssetCollectionChangeRequest(for: album),
            let photoPlaceholder = changeRequest.placeholderForCreatedAsset else { return }

        placeholder = photoPlaceholder
        let fastEnumeration = NSArray(array: [photoPlaceholder] as [PHObjectPlaceholder])
        albumChangeRequest.addAssets(fastEnumeration)
    }, completionHandler: { success, error in
        guard let placeholder = placeholder else {
            completion?(nil)
            return
        }

        if success {
            let assets:PHFetchResult<PHAsset> =  PHAsset.fetchAssets(withLocalIdentifiers: [placeholder.localIdentifier], options: nil)
            let asset:PHAsset? = assets.firstObject
            completion?(asset)
        }
        else {
            completion?(nil)
        }
    })
}

func mergeImageData(imageData: Data, with metadata: NSDictionary) -> Data {
    let source: CGImageSource = CGImageSourceCreateWithData(imageData as NSData, nil)!
    let UTI: CFString = CGImageSourceGetType(source)!
    let newImageData =  NSMutableData()
    let cgImage = UIImage(data: imageData)!.cgImage
    let imageDestination: CGImageDestination = CGImageDestinationCreateWithData((newImageData as CFMutableData), UTI, 1, nil)!
    CGImageDestinationAddImage(imageDestination, cgImage!, metadata as CFDictionary)
    CGImageDestinationFinalize(imageDestination)

    return newImageData as Data
}