Taking a dng picture using the Camera2 API

I'm creating an app that takes pictures in .dng format in order to process them. I'm using the camera2 API. I was able to take pictures and save them into my phone, but in .jpg format. But when I change my code in order to save them with .dng extension, it compiles, show me the preview on my phone, but when the picture is taken, I get an error. The part of my code that takes and saves the picture is as follows.

val reader = ImageReader.newInstance(1280, 720, ImageFormat.RAW_SENSOR, 1)

val outputSurfaces = ArrayList<Surface>(2)
outputSurfaces.add(reader.surface)
outputSurfaces.add(Surface(previewTextureView.surfaceTexture))

val captureBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE)
captureBuilder.addTarget(reader.surface)
captureBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO)

val file = File("myPath/myImageName.dng")
var captureResult: CaptureResult? = null

And my listeners :

val readerListener = object : ImageReader.OnImageAvailableListener {
    override fun onImageAvailable(reader: ImageReader) {
        var image: Image? = null
        var output: OutputStream? = null
        val dngCreator = DngCreator(cameraManager.getCameraCharacteristics("0"), captureResult)

        try {
             image = reader.acquireLatestImage()
             output = FileOutputStream(file)
             dngCreator.writeImage(output, image)
         } catch (e: FileNotFoundException) {
             e.printStackTrace()
         } catch (e: IOException) {
             e.printStackTrace()
         } finally {
             output?.close()
             image?.close()
         }
    }
}

reader.setOnImageAvailableListener(readerListener, backgroundHandler)

val captureListener = object : CameraCaptureSession.CaptureCallback() {
    override fun onCaptureCompleted(session: CameraCaptureSession, request: CaptureRequest, result: TotalCaptureResult) {
        captureResult = result
        super.onCaptureCompleted(session, request, result)
    }
}

And finally I capture the session with:

cameraDevice.createCaptureSession(outputSurfaces, object : CameraCaptureSession.StateCallback() {
    override fun onConfigured(session: CameraCaptureSession) {
        try {
             session.capture(captureBuilder.build(), captureListener, backgroundHandler)
         } catch (e: CameraAccessException) {
              e.printStackTrace()
         }
     }
     override fun onConfigureFailed(session: CameraCaptureSession) {}
}, backgroundHandler)

I'm having one warning and one error that I didn't have before, when I was saving the image as jpeg:

W/CameraDevice-JV-0: Stream configuration failed due to: createSurfaceFromGbp:1106: Camera 0: No supported stream configurations with format 0x20 defined, failed to create output stream

E/CameraCaptureSession: Session 1: Failed to create capture session; configuration failed

Things that I changed in order to save a dng file are :

• I replaced ImageFormat.JPEG with ImageFormat.RAW_SENSOR
• I changed the file extension from .jpg to .dng
• Instead of using dngCreator.writeImage(output, image), I used :

val buffer = image!!.planes[0].buffer
val bytes = ByteArray(buffer.capacity())
buffer.get(bytes)
output.write()

Since there is not a lot of information about this subject, I'm not sure if my implementation is correct.

After some research, I found a implementation in order to save an image that was taken with the Camera2API, in a .dng file :

if (mImage.format == ImageFormat.RAW_SENSOR) {
    val dngCreator = DngCreator(mCharacteristics, mCaptureResult)
    var output: FileOutputStream? = null
    try {
        output = FileOutputStream(mFile)
        dngCreator.writeImage(output, mImage)
    } catch (e: IOException) {
         e.printStackTrace()
    } finally {
         mImage.close()
         closeOutput(output)
     }
}

Where :

• mCharacteristics are CameraCharacteristics, ie the properties describing the CameraDevice
• mCaptureResult is produced by the CameraDevice after processing the CaptureRequest
• mImage is the image retrieved in the function dequeuAndSaveImage : image = reader.get()!!.acquireNextImage()
• mFile is the File where the image will be saved, for example :

mFile = Environment
     .getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),
     "RAW_" + generateTimestamp()+ ".dng"

Maybe it will help somebody, but as @Alex Cohn said, it's recommended to begin with the official sample github.com/googlesamples/android-Camera2Raw. It's written in Java and not in Kotlin, but it's not that hard to transform it, if needed.