如何使用flutter检测图像是否全黑？

import 'dart:io';
import 'dart:ui';
import 'package:flutter/material.dart';
import 'package:image_picker/image_picker.dart';
import 'package:path_provider/path_provider.dart';

class ImageDetectionPage extends StatefulWidget {
  @override
  _ImageDetectionPageState createState() => _ImageDetectionPageState();
}

class _ImageDetectionPageState extends State<ImageDetectionPage> {
  File _imageFile;
  bool _isImageBlack = false;

  Future<void> _getImage() async {
    final imagePicker = ImagePicker();
    final pickedImage = await imagePicker.getImage(source: ImageSource.gallery);

    if (pickedImage != null) {
      final imageFile = File(pickedImage.path);
      final grayImage = await convertToGrayScale(imageFile);
      final isBlack = checkIfImageIsBlack(grayImage);

      setState(() {
        _imageFile = imageFile;
        _isImageBlack = isBlack;
      });
    }
  }

  Future<File> convertToGrayScale(File imageFile) async {
    final image = await decodeImageFromList(await imageFile.readAsBytes());
    final grayImage = File('${(await getTemporaryDirectory()).path}/gray_image.png');

    final gray = grayscale(image);
    await grayImage.writeAsBytes(encodePng(gray));

    return grayImage;
  }

  Image grayscale(Image image) {
    final grayscale = image.clone();
    for (int x = 0; x < grayscale.width; x++) {
      for (int y = 0; y < grayscale.height; y++) {
        final pixel = grayscale.getPixel(x, y);
        final gray = getGrayScale(pixel);
        grayscale.setPixel(x, y, Color(gray, gray, gray).value);
      }
    }
    return grayscale;
  }

  int getGrayScale(int color) {
    final red = getRed(color);
    final green = getGreen(color);
    final blue = getBlue(color);
    return ((red + green + blue) / 3).round();
  }

  int getRed(int color) => color >> 16 & 0xFF;

  int getGreen(int color) => color >> 8 & 0xFF;

  int getBlue(int color) => color & 0xFF;

  bool checkIfImageIsBlack(File imageFile) {
    final image = decodeImage(imageFile.readAsBytesSync());
    for (int x = 0; x < image.width; x++) {
      for (int y = 0; y < image.height; y++) {
        final pixel = image.getPixel(x, y);
        if (getGrayScale(pixel) != 0) {
          return false;
        }
      }
    }
    return true;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Image Detection'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            if (_imageFile != null)
              Image.file(
                _imageFile,
                width: 200,
                height: 200,
              ),
            SizedBox(height: 20),
            if (_imageFile != null)
              Text(
                _isImageBlack ? 'The image is fully black' : 'The image is not fully black',
                style: TextStyle(fontSize: 18),
              ),
            SizedBox(height: 20),
            ElevatedButton(
              onPressed: _getImage,
              child: Text('Select Image'),
            ),
          ],
        ),
      ),
    );
  }
}