Can you save an edited RAW .dng file on iOS?

Question

I want to build an iOS 10 app that lets you shoot a RAW (.dng) image, edit it, and then saved the edited .dng file to the camera roll. By combining

Answer 1

The only way to get DNG data as of the writing of this response (iOS 10.1) is:

AVCapturePhotoOutput.dngPhotoDataRepresentation(forRawSampleBuffer: CMSampleBuffer, previewPhotoSampleBuffer: CMSampleBuffer?) 

Noting the OP refers to Core Image. As mentioned by rickster, CI works on processed image data, therefore only offers processed image results (JPEG, TIFF):

CIContext.writeJPEGRepresentation(of:to:colorSpace:options:)
CIContext.writeTIFFRepresentation(of:to:format:colorSpace:options:)