Machine Learning

Skill 20: Machine Learning Integration

Overview

This skill enables machine learning capabilities in Flutter applications using TensorFlow Lite and Firebase ML Kit. Supports image classification, object detection, text recognition, and custom model deployment.

Features

• Image classification with pre-trained models
• Object detection and tracking
• Text recognition (OCR)
• Face detection
• Barcode scanning
• Custom TFLite model integration
• On-device inference
• Cloud-based ML with Firebase

Installation

Dependencies

dependencies:
  tflite_flutter: ^0.10.4
  tflite_flutter_helper: ^0.3.1
  firebase_ml_model_downloader: ^0.2.4
  google_mlkit_text_recognition: ^0.11.0
  google_mlkit_face_detection: ^0.9.0
  google_mlkit_barcode_scanning: ^0.10.0
  google_mlkit_object_detection: ^0.11.0
  image_picker: ^1.0.7
  image: ^4.1.3

Image Classification

1. Model Setup

Add your TensorFlow Lite model to assets/models/:

# pubspec.yaml
flutter:
  assets:
    - assets/models/model.tflite
    - assets/labels/labels.txt

2. Image Classification Service

import 'package:tflite_flutter/tflite_flutter.dart';
import 'package:image/image.dart' as img;
import 'dart:io';

class ImageClassifier {
  Interpreter? _interpreter;
  List<String>? _labels;

  Future<void> loadModel() async {
    try {
      _interpreter = await Interpreter.fromAsset('assets/models/model.tflite');

      // Load labels
      final labelData = await rootBundle.loadString('assets/labels/labels.txt');
      _labels = labelData.split('\n');
    } catch (e) {
      print('Error loading model: $e');
    }
  }

  Future<Map<String, double>> classifyImage(File imageFile) async {
    if (_interpreter == null) {
      throw Exception('Model not loaded');
    }

    // Load and preprocess image
    final imageData = await imageFile.readAsBytes();
    var image = img.decodeImage(imageData)!;

    // Resize to model input size (e.g., 224x224)
    image = img.copyResize(image, width: 224, height: 224);

    // Convert to input format
    final input = _imageToInputList(image);

    // Run inference
    final output = List.filled(1 * _labels!.length, 0).reshape([1, _labels!.length]);
    _interpreter!.run(input, output);

    // Process results
    final results = <String, double>{};
    for (int i = 0; i < _labels!.length; i++) {
      results[_labels![i]] = output[0][i];
    }

    return results;
  }

  List<List<List<List<double>>>> _imageToInputList(img.Image image) {
    final input = List.generate(
      1,
      (_) => List.generate(
        224,
        (y) => List.generate(
          224,
          (x) {
            final pixel = image.getPixel(x, y);
            return [
              pixel.r / 255.0,
              pixel.g / 255.0,
              pixel.b / 255.0,
            ];
          },
        ),
      ),
    );
    return input;
  }

  void dispose() {
    _interpreter?.close();
  }
}

3. Classification UI

class ImageClassificationPage extends ConsumerStatefulWidget {
  const ImageClassificationPage({super.key});

  @override
  ConsumerState<ImageClassificationPage> createState() => _ImageClassificationPageState();
}

class _ImageClassificationPageState extends ConsumerState<ImageClassificationPage> {
  final ImageClassifier _classifier = ImageClassifier();
  File? _selectedImage;
  Map<String, double>? _results;
  bool _isLoading = false;

  @override
  void initState() {
    super.initState();
    _classifier.loadModel();
  }

  Future<void> _pickImage() async {
    final picker = ImagePicker();
    final picked = await picker.pickImage(source: ImageSource.gallery);

    if (picked != null) {
      setState(() {
        _selectedImage = File(picked.path);
        _isLoading = true;
      });

      final results = await _classifier.classifyImage(_selectedImage!);

      setState(() {
        _results = results;
        _isLoading = false;
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Image Classification')),
      body: Column(
        children: [
          if (_selectedImage != null)
            Image.file(_selectedImage!, height: 300),
          const SizedBox(height: 20),
          if (_isLoading)
            const CircularProgressIndicator()
          else if (_results != null)
            Expanded(
              child: ListView.builder(
                itemCount: _results!.length,
                itemBuilder: (context, index) {
                  final label = _results!.keys.elementAt(index);
                  final confidence = _results![label]!;

                  return ListTile(
                    title: Text(label),
                    trailing: Text('${(confidence * 100).toStringAsFixed(1)}%'),
                    subtitle: LinearProgressIndicator(
                      value: confidence,
                    ),
                  );
                },
              ),
            ),
        ],
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _pickImage,
        child: const Icon(Icons.image),
      ),
    );
  }

  @override
  void dispose() {
    _classifier.dispose();
    super.dispose();
  }
}

Text Recognition (OCR)

import 'package:google_mlkit_text_recognition/google_mlkit_text_recognition.dart';

class TextRecognitionService {
  final TextRecognizer _textRecognizer = TextRecognizer();

  Future<String> recognizeText(File imageFile) async {
    final inputImage = InputImage.fromFile(imageFile);
    final recognizedText = await _textRecognizer.processImage(inputImage);

    return recognizedText.text;
  }

  Future<List<TextBlock>> recognizeTextBlocks(File imageFile) async {
    final inputImage = InputImage.fromFile(imageFile);
    final recognizedText = await _textRecognizer.processImage(inputImage);

    return recognizedText.blocks;
  }

  void dispose() {
    _textRecognizer.close();
  }
}

class OCRWidget extends StatefulWidget {
  const OCRWidget({super.key});

  @override
  State<OCRWidget> createState() => _OCRWidgetState();
}

class _OCRWidgetState extends State<OCRWidget> {
  final TextRecognitionService _service = TextRecognitionService();
  File? _image;
  String _recognizedText = '';

  Future<void> _scanText() async {
    final picker = ImagePicker();
    final picked = await picker.pickImage(source: ImageSource.camera);

    if (picked != null) {
      setState(() => _image = File(picked.path));

      final text = await _service.recognizeText(_image!);
      setState(() => _recognizedText = text);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SingleChildScrollView(
        padding: const EdgeInsets.all(16),
        child: Column(
          children: [
            if (_image != null)
              Image.file(_image!, height: 200),
            const SizedBox(height: 20),
            ElevatedButton(
              onPressed: _scanText,
              child: const Text('Scan Text'),
            ),
            const SizedBox(height: 20),
            Text(
              'Recognized Text:',
              style: Theme.of(context).textTheme.titleLarge,
            ),
            const SizedBox(height: 10),
            Text(_recognizedText),
          ],
        ),
      ),
    );
  }

  @override
  void dispose() {
    _service.dispose();
    super.dispose();
  }
}

Object Detection

import 'package:google_mlkit_object_detection/google_mlkit_object_detection.dart';

class ObjectDetectionService {
  late ObjectDetector _objectDetector;

  void initialize() {
    final options = ObjectDetectorOptions(
      mode: DetectionMode.single,
      classifyObjects: true,
      trackMultipleObjects: true,
    );
    _objectDetector = ObjectDetector(options: options);
  }

  Future<List<DetectedObject>> detectObjects(File imageFile) async {
    final inputImage = InputImage.fromFile(imageFile);
    return await _objectDetector.processImage(inputImage);
  }

  void dispose() {
    _objectDetector.close();
  }
}

class ObjectDetectionPainter extends CustomPainter {
  final List<DetectedObject> objects;
  final Size imageSize;

  ObjectDetectionPainter({required this.objects, required this.imageSize});

  @override
  void paint(Canvas canvas, Size size) {
    final paint = Paint()
      ..style = PaintingStyle.stroke
      ..strokeWidth = 3.0
      ..color = Colors.green;

    final textPainter = TextPainter(
      textDirection: TextDirection.ltr,
    );

    for (final object in objects) {
      final rect = _scaleRect(object.boundingBox, imageSize, size);
      canvas.drawRect(rect, paint);

      // Draw label
      if (object.labels.isNotEmpty) {
        final label = object.labels.first;
        textPainter.text = TextSpan(
          text: '${label.text} ${(label.confidence * 100).toStringAsFixed(0)}%',
          style: const TextStyle(
            color: Colors.green,
            fontSize: 16,
            fontWeight: FontWeight.bold,
            backgroundColor: Colors.white,
          ),
        );
        textPainter.layout();
        textPainter.paint(canvas, Offset(rect.left, rect.top - 20));
      }
    }
  }

  Rect _scaleRect(Rect rect, Size imageSize, Size canvasSize) {
    final scaleX = canvasSize.width / imageSize.width;
    final scaleY = canvasSize.height / imageSize.height;

    return Rect.fromLTRB(
      rect.left * scaleX,
      rect.top * scaleY,
      rect.right * scaleX,
      rect.bottom * scaleY,
    );
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => true;
}

Barcode Scanning

import 'package:google_mlkit_barcode_scanning/google_mlkit_barcode_scanning.dart';

class BarcodeScannerService {
  final BarcodeScanner _scanner = BarcodeScanner();

  Future<List<Barcode>> scanBarcodes(File imageFile) async {
    final inputImage = InputImage.fromFile(imageFile);
    return await _scanner.processImage(inputImage);
  }

  void dispose() {
    _scanner.close();
  }
}

// Real-time barcode scanning with camera
class BarcodeScannerPage extends StatefulWidget {
  const BarcodeScannerPage({super.key});

  @override
  State<BarcodeScannerPage> createState() => _BarcodeScannerPageState();
}

class _BarcodeScannerPageState extends State<BarcodeScannerPage> {
  CameraController? _cameraController;
  final BarcodeScanner _scanner = BarcodeScanner();
  bool _isProcessing = false;
  String? _scannedBarcode;

  @override
  void initState() {
    super.initState();
    _initializeCamera();
  }

  Future<void> _initializeCamera() async {
    final cameras = await availableCameras();
    _cameraController = CameraController(
      cameras.first,
      ResolutionPreset.medium,
      enableAudio: false,
    );

    await _cameraController!.initialize();
    await _cameraController!.startImageStream(_processCameraImage);

    setState(() {});
  }

  Future<void> _processCameraImage(CameraImage image) async {
    if (_isProcessing) return;
    _isProcessing = true;

    try {
      final WriteBuffer allBytes = WriteBuffer();
      for (final Plane plane in image.planes) {
        allBytes.putUint8List(plane.bytes);
      }
      final bytes = allBytes.done().buffer.asUint8List();

      final imageSize = Size(image.width.toDouble(), image.height.toDouble());

      final inputImage = InputImage.fromBytes(
        bytes: bytes,
        metadata: InputImageMetadata(
          size: imageSize,
          rotation: InputImageRotation.rotation0,
          format: InputImageFormat.nv21,
          bytesPerRow: image.planes.first.bytesPerRow,
        ),
      );

      final barcodes = await _scanner.processImage(inputImage);

      if (barcodes.isNotEmpty) {
        setState(() {
          _scannedBarcode = barcodes.first.rawValue;
        });
      }
    } finally {
      _isProcessing = false;
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Scan Barcode')),
      body: Stack(
        children: [
          if (_cameraController != null)
            CameraPreview(_cameraController!),
          if (_scannedBarcode != null)
            Center(
              child: Container(
                padding: const EdgeInsets.all(16),
                color: Colors.black54,
                child: Text(
                  'Scanned: $_scannedBarcode',
                  style: const TextStyle(color: Colors.white, fontSize: 20),
                ),
              ),
            ),
        ],
      ),
    );
  }

  @override
  void dispose() {
    _cameraController?.dispose();
    _scanner.close();
    super.dispose();
  }
}

Firebase ML Model Download

import 'package:firebase_ml_model_downloader/firebase_ml_model_downloader.dart';

class FirebaseMLService {
  Future<void> downloadModel(String modelName) async {
    final model = await FirebaseModelDownloader.instance.getModel(
      modelName,
      FirebaseModelDownloadType.localModel,
      FirebaseModelDownloadConditions(
        iosAllowsCellularAccess: true,
        iosAllowsBackgroundDownloading: false,
        androidChargingRequired: false,
        androidWifiRequired: false,
        androidDeviceIdleRequired: false,
      ),
    );

    print('Model downloaded to: ${model.file}');
  }
}

Best Practices

1. Load models asynchronously - Don't block UI thread
2. Dispose properly - Release model resources
3. Use quantized models - Smaller, faster inference
4. Cache results - Avoid re-processing same images
5. Handle low confidence - Filter results below threshold
6. Test on real devices - Simulators may not support ML

Performance Optimization

class OptimizedMLService {
  Interpreter? _interpreter;
  bool _isModelLoaded = false;

  Future<void> loadModel() async {
    if (_isModelLoaded) return;

    final options = InterpreterOptions()
      ..threads = 4  // Use multiple threads
      ..useNnApiForAndroid = true;  // Use NNAPI acceleration

    _interpreter = await Interpreter.fromAsset(
      'model.tflite',
      options: options,
    );

    _isModelLoaded = true;
  }

  // Process multiple images in batch
  Future<List<dynamic>> batchInference(List<File> images) async {
    final results = <dynamic>[];

    for (final image in images) {
      final result = await _singleInference(image);
      results.add(result);
    }

    return results;
  }

  Future<dynamic> _singleInference(File image) async {
    // Preprocess and run inference
    // ...
  }
}

Troubleshooting

Model not loading

• Check model format is valid TFLite
• Verify model path is correct
• Ensure model is included in pubspec.yaml

Out of memory

• Use smaller input sizes
• Load model on-demand, not at startup
• Dispose models when not needed

Slow inference

• Use quantized models (INT8)
• Enable NNAPI/GPU delegates
• Reduce image resolution