I use the official api to output the raw file. when I transfer it to my mac, it is very dark. But if I shot with iOS original camera app, it is brighter.
This is how I save the proraw file to photo library
let creationRequest = PHAssetCreationRequest.forAsset()
creationRequest.addResource(with: .photo,
data: photo.compressedData,
options: nil)
// Save the RAW (DNG) file an alternate resource for the Photos asset.
let options = PHAssetResourceCreationOptions()
////////options.shouldMoveFile = true
creationRequest.addResource(with: .alternatePhoto,
fileURL: photo.rawFileURL,
options: options)