flutter real time face detection - opencv

Question

I am currently developing an app that requires real time face detection. Right now I have the mlkit library in the app and I am using the firebase face detector. At the moment, it produces an error every time I try to detect a face from file:
DynamiteModule(13840): Local module descriptor class for com.google.android.gms.vision.dynamite.face not found.
As for the real time part, I tried using the RepaintBoundary in flutter to get a screenshot of the camera widget (almost)every frame and convert it into a binary file for face detection. But for some reason, flutter crashed every time I tried to screenshot the camera widget. It worked for other widgets.
After coming across both of these problems and spending quite a while trying to solve them, I've been thinking about just doing the camera part of the app in android/iOS native code(I would do this with OpenCV so that I can have real time detection). Is there a way I could use platform channels to implement a camera view in kotlin and swift and import that to a flutter widget? Or is there another easier way to implement this?

Answer 1

For the real-time access to camera image stream, I answered in another question How to access camera frames in flutter quickly that you want to use CameraController#startImageStream
import 'package:camera/camera.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
void main() => runApp(MaterialApp(home: _MyHomePage()));
class _MyHomePage extends StatefulWidget {
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<_MyHomePage> {
dynamic _scanResults;
CameraController _camera;
bool _isDetecting = false;
CameraLensDirection _direction = CameraLensDirection.back;
#override
void initState() {
super.initState();
_initializeCamera();
}
Future<CameraDescription> _getCamera(CameraLensDirection dir) async {
return await availableCameras().then(
(List<CameraDescription> cameras) => cameras.firstWhere(
(CameraDescription camera) => camera.lensDirection == dir,
),
);
}
void _initializeCamera() async {
_camera = CameraController(
await _getCamera(_direction),
defaultTargetPlatform == TargetPlatform.iOS
? ResolutionPreset.low
: ResolutionPreset.medium,
);
await _camera.initialize();
_camera.startImageStream((CameraImage image) {
if (_isDetecting) return;
_isDetecting = true;
try {
// await doOpenCVDectionHere(image)
} catch (e) {
// await handleExepction(e)
} finally {
_isDetecting = false;
}
});
}
Widget build(BuildContext context) {
return null;
}
}

Answer 2

I did something this with OpenCV before, my solution was:
Start a new Activity or ViewController on Android and iOS respectively via platform channel. Example:
class FaceScanPlugin(val activity: Activity) : MethodCallHandler, PluginRegistry.ActivityResultListener {
var result: Result? = null
companion object {
#JvmStatic
fun registerWith(registrar: Registrar): Unit {
val channel = MethodChannel(registrar.messenger(), "com.example.facescan")
val plugin = BarcodeScanPlugin(registrar.activity())
channel.setMethodCallHandler(plugin)
registrar.addActivityResultListener(plugin)
}
}
override fun onMethodCall(call: MethodCall, result: Result): Unit {
if (call.method.equals("scan")) {
this.result = result
showFaceScanView()
} else {
result.notImplemented()
}
}
private fun showFaceScanView() {
val intent = Intent(activity, FaceScannerActivity::class.java)
activity.startActivityForResult(intent, 100)
}
override fun onActivityResult(code: Int, resultCode: Int, data: Intent?): Boolean {
if (code == 100) {
if (resultCode == Activity.RESULT_OK) {
return true
}
}
return false
}
}
Refer to Flutter QR scanner plugin on how to navigate to Android activity or iOS View.
Then do your OpenCV real-time face detection via Camera2 and AVFoundation.
Other than that, I supposed you can try out the new AndroidView or UIKitView if you want to embed the android or iOS into your Flutter app.