tflite detection error repro

bndbox.dart

// Based on https://github.com/shaqian/flutter_realtime_detection

import 'package:flutter/material.dart' show Border, BoxDecoration, BuildContext, Color, Container, EdgeInsets, FontWeight, Positioned, Stack, StatelessWidget, Text, TextStyle, Widget;
import 'dart:math' as math;

class BndBox extends StatelessWidget {
  final List<dynamic> results;
  final int previewH;
  final int previewW;
  final double screenH;
  final double screenW;

  BndBox(this.results, this.previewH, this.previewW, this.screenH, this.screenW);

  @override
  Widget build(BuildContext context) {
    List<Widget> _renderBoxes() {
      return results.map((re) {
        var _x = re["rect"]["x"];
        var _w = re["rect"]["w"];
        var _y = re["rect"]["y"];
        var _h = re["rect"]["h"];
        var scaleW, scaleH, x, y, w, h;

        if (screenH / screenW > previewH / previewW) {
          scaleW = screenH / previewH * previewW;
          scaleH = screenH;
          var difW = (scaleW - screenW) / scaleW;
          x = (_x - difW / 2) * scaleW;
          w = _w * scaleW;
          if (_x < difW / 2) w -= (difW / 2 - _x) * scaleW;
          y = _y * scaleH;
          h = _h * scaleH;
        } else {
          scaleH = screenW / previewW * previewH;
          scaleW = screenW;
          var difH = (scaleH - screenH) / scaleH;
          x = _x * scaleW;
          w = _w * scaleW;
          y = (_y - difH / 2) * scaleH;
          h = _h * scaleH;
          if (_y < difH / 2) h -= (difH / 2 - _y) * scaleH;
        }

        return Positioned(
          left: math.max(0, x),
          top: math.max(0, y),
          width: w,
          height: h,
          child: Container(
            padding: EdgeInsets.only(top: 5.0, left: 5.0),
            decoration: BoxDecoration(
              border: Border.all(
                color: Color.fromRGBO(37, 213, 253, 1.0),
                width: 3.0,
              ),
            ),
            child: Text(
              "${re["detectedClass"]} ${(re["confidenceInClass"] * 100).toStringAsFixed(0)}%",
              style: TextStyle(
                color: Color.fromRGBO(37, 213, 253, 1.0),
                fontSize: 14.0,
                fontWeight: FontWeight.bold,
              ),
            ),
          ),
        );
      }).toList();
    }

    return Stack(
      children: _renderBoxes(),
    );
  }
}

camera.dart

// Based on https://github.com/shaqian/flutter_realtime_detection

import 'package:flutter/material.dart' show BuildContext, Container, MediaQuery, OverflowBox, State, StatefulWidget, Widget;
import 'package:camera/camera.dart';
import 'package:tflite/tflite.dart';
import 'dart:math' as math;

typedef void Callback(List<dynamic> list, int h, int w);

class Camera extends StatefulWidget {
  final List<CameraDescription> cameras;
  final Callback setRecognitions;

  Camera(this.cameras, this.setRecognitions);

  @override
  _CameraState createState() => new _CameraState();
}

class _CameraState extends State<Camera> {
  CameraController controller;
  bool isDetecting = false;

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

    if (widget.cameras == null || widget.cameras.length < 1) {
      print('No camera is found');
    } else {
      controller = new CameraController(
        widget.cameras[0],
        ResolutionPreset.high,
      );
      controller.initialize().then((_) {
        if (!mounted) {
          return;
        }
        setState(() {});

        controller.startImageStream((CameraImage img) {
          if (!isDetecting) {
            isDetecting = true;

            int startTime = new DateTime.now().millisecondsSinceEpoch;

            Tflite.detectObjectOnFrame(
              bytesList: img.planes.map((plane) {
                return plane.bytes;
              }).toList(),
              model: "SSDMobileNet",
              imageHeight: img.height,
              imageWidth: img.width,
              imageMean: 127.5,
              imageStd: 127.5,
              numResultsPerClass: 1,
              threshold: 0.4,
            ).then((recognitions) {
              int endTime = new DateTime.now().millisecondsSinceEpoch;
              print("Detection took ${endTime - startTime}");

              widget.setRecognitions(recognitions, img.height, img.width);

              isDetecting = false;
            });
          }
        });
      });
    }
  }

  @override
  void dispose() {
    controller?.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    if (controller == null || !controller.value.isInitialized) {
      return Container();
    }

    var tmp = MediaQuery.of(context).size;
    var screenH = math.max(tmp.height, tmp.width);
    var screenW = math.min(tmp.height, tmp.width);
    tmp = controller.value.previewSize;
    var previewH = math.max(tmp.height, tmp.width);
    var previewW = math.min(tmp.height, tmp.width);
    var screenRatio = screenH / screenW;
    var previewRatio = previewH / previewW;

    return OverflowBox(
      maxHeight:
          screenRatio > previewRatio ? screenH : screenW / previewW * previewH,
      maxWidth:
          screenRatio > previewRatio ? screenH / previewH * previewW : screenW,
      child: CameraPreview(controller),
    );
  }
}

home.dart

// Based on https://github.com/shaqian/flutter_realtime_detection

import 'package:flutter/material.dart' show BuildContext, MediaQuery, Scaffold, Size, Stack, State, StatefulWidget, Widget;
import 'package:camera/camera.dart';
import 'package:tflite/tflite.dart';
import 'dart:math' as math;

import 'camera.dart';
import 'bndbox.dart';

class HomePage extends StatefulWidget {
  final List<CameraDescription> cameras;

  HomePage(this.cameras);

  @override
  _HomePageState createState() => new _HomePageState();
}

class _HomePageState extends State<HomePage> {
  List<dynamic> _recognitions;
  int _imageHeight = 0;
  int _imageWidth = 0;

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

  void loadModel() async {
    await Tflite.loadModel(
        model: "assets/routespotter_model.tflite",
        labels: "assets/labels.txt");
  }

  setRecognitions(recognitions, imageHeight, imageWidth) {
    setState(() {
      _recognitions = recognitions;
      _imageHeight = imageHeight;
      _imageWidth = imageWidth;
    });
  }

  @override
  Widget build(BuildContext context) {
    Size screen = MediaQuery.of(context).size;
    return Scaffold(
      body: Stack(
        children: [
          Camera(
            widget.cameras,
            setRecognitions,
          ),
          BndBox(
              _recognitions == null ? [] : _recognitions,
              math.max(_imageHeight, _imageWidth),
              math.min(_imageHeight, _imageWidth),
              screen.height,
              screen.width),
        ],
      ),
    );
  }
}

main.dart

// Based on https://github.com/shaqian/flutter_realtime_detection

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:camera/camera.dart' show CameraDescription, CameraException, availableCameras;
import 'home.dart';

List<CameraDescription> cameras;
import 'package:flutter/material.dart' show Border, BoxDecoration, BuildContext, Color, Container, EdgeInsets, FontWeight, Positioned, Stack, StatelessWidget, Text, TextStyle, Widget;
import 'dart:math' as math;

class BndBox extends StatelessWidget {
  final List<dynamic> results;
  final int previewH;
  final int previewW;
  final double screenH;
  final double screenW;

  BndBox(this.results, this.previewH, this.previewW, this.screenH, this.screenW);

  @override
  Widget build(BuildContext context) {
    List<Widget> _renderBoxes() {
      return results.map((re) {
        var _x = re["rect"]["x"];
        var _w = re["rect"]["w"];
        var _y = re["rect"]["y"];
        var _h = re["rect"]["h"];
        var scaleW, scaleH, x, y, w, h;

        if (screenH / screenW > previewH / previewW) {
          scaleW = screenH / previewH * previewW;
          scaleH = screenH;
          var difW = (scaleW - screenW) / scaleW;
          x = (_x - difW / 2) * scaleW;
          w = _w * scaleW;
          if (_x < difW / 2) w -= (difW / 2 - _x) * scaleW;
          y = _y * scaleH;
          h = _h * scaleH;
        } else {
          scaleH = screenW / previewW * previewH;
          scaleW = screenW;
          var difH = (scaleH - screenH) / scaleH;
          x = _x * scaleW;
          w = _w * scaleW;
          y = (_y - difH / 2) * scaleH;
          h = _h * scaleH;
          if (_y < difH / 2) h -= (difH / 2 - _y) * scaleH;
        }

        return Positioned(
          left: math.max(0, x),
          top: math.max(0, y),
          width: w,
          height: h,
          child: Container(
            padding: EdgeInsets.only(top: 5.0, left: 5.0),
            decoration: BoxDecoration(
              border: Border.all(
                color: Color.fromRGBO(37, 213, 253, 1.0),
                width: 3.0,
              ),
            ),
            child: Text(
              "${re["detectedClass"]} ${(re["confidenceInClass"] * 100).toStringAsFixed(0)}%",
              style: TextStyle(
                color: Color.fromRGBO(37, 213, 253, 1.0),
                fontSize: 14.0,
                fontWeight: FontWeight.bold,
              ),
            ),
          ),
        );
      }).toList();
    }

    return Stack(
      children: _renderBoxes(),
    );
  }
}

Future<Null> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  try {
    cameras = await availableCameras();
  } on CameraException catch (e) {
    print('Error: $e.code\nError Message: $e.message');
  }
  runApp(new MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'tflite real-time detection',
      theme: ThemeData(
        brightness: Brightness.dark,
      ),
      home: HomePage(cameras),
    );
  }
}