A simple Flutter app that applies image filters before exporting it in PDF.

image_to_pdf_simple_app.dart

import 'dart:io';
import 'dart:typed_data';
import 'package:flutter/material.dart';
import 'package:image_picker/image_picker.dart';
import 'package:image/image.dart' as img;
import 'package:open_file/open_file.dart';
import 'package:pdf/widgets.dart' as pw;
import 'package:path_provider/path_provider.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Image to PDF App',
      theme: ThemeData(primarySwatch: Colors.blue),
      home: const ImageToPdfPage(),
    );
  }
}

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

  @override
  State<ImageToPdfPage> createState() => _ImageToPdfPageState();
}

class _ImageToPdfPageState extends State<ImageToPdfPage> {
  File? _image;
  img.Image? _filteredImage;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Image to PDF App')),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            _filteredImage != null
                ? Image.memory(
                    Uint8List.fromList(
                      img.encodeJpg(_filteredImage!),
                    ),
                  )
                : const Text('No image selected.'),
            const SizedBox(height: 20),
            ElevatedButton(
              child: const Text('Select Image'),
              onPressed: () async {
                final pickedFile = await ImagePicker().pickImage(
                  source: ImageSource.camera,
                );

                if (pickedFile != null) {
                  setState(() {
                    _image = File(pickedFile.path);
                    _filteredImage = img.decodeImage(
                      _image!.readAsBytesSync(),
                    );
                  });
                }
              },
            ),
            const SizedBox(height: 20),
            DropdownButton<String>(
              items: [
                'Original',
                'Enhanced',
                'Grayscale',
                'Sepia',
              ].map((String filter) {
                return DropdownMenuItem<String>(
                  value: filter,
                  child: Text(filter),
                );
              }).toList(),
              onChanged: (selectedFilter) {
                setState(() {
                  if (_image != null && selectedFilter != null) {
                    _filteredImage = applyFilter(_image!, selectedFilter);
                  }
                });
              },
              hint: const Text('Choose a filter'),
            ),
            const SizedBox(height: 20),
            ElevatedButton(
              child: const Text('Convert to PDF'),
              onPressed: () async {
                if (_filteredImage != null) {
                  await convertToPdf(_filteredImage!).then(
                    (pdfFile) {
                      ScaffoldMessenger.of(context).showSnackBar(
                        SnackBar(
                          content: Text('PDF saved at: ${pdfFile.path}'),
                          action: SnackBarAction(
                            label: 'Open',
                            onPressed: () {
                              OpenFile.open(pdfFile.path);
                            },
                          ),
                        ),
                      );
                    },
                  );
                }
              },
            ),
          ],
        ),
      ),
    );
  }

  img.Image applyFilter(File imageFile, String filter) {
    final image = img.decodeImage(imageFile.readAsBytesSync())!;
    switch (filter) {
      case 'Enhanced':
        return enhanceImage(image);
      case 'Grayscale':
        return img.grayscale(image);
      case 'Sepia':
        return img.sepia(image);
      default:
        return image;
    }
  }

  img.Image enhanceImage(img.Image image) {
    img.adjustColor(image, contrast: 1.5, brightness: 10);
    return image;
  }

  Future<File> convertToPdf(img.Image image) async {
    final pdf = pw.Document();
    final pdfImage = pw.MemoryImage(img.encodeJpg(image));
    pdf.addPage(
      pw.Page(
        build: (pw.Context context) => pw.Center(
          child: pw.Image(pdfImage),
        ),
      ),
    );
    final pdfBytes = pdf.save();
    final Directory documentDirectory =
        await getApplicationDocumentsDirectory();
    final String documentPath = documentDirectory.path;
    final File receiptFile = File('$documentPath/example.pdf');
    receiptFile.writeAsBytesSync(List.from(await pdfBytes));
    return receiptFile;
  }
}