Flutter resize image before upload

Question

I need to resize images before uploading to the server.

I am using io and image package.

import 'dart:io';  
import 'package:image/image.dart' as Img;

using this function

uploadImages(File image_File) async {

    Img.Image image_temp = Img.decodeImage(image_File.readAsBytesSync());

    Img.Image resized_img = Img.copyResize(image_temp, 800);

    File resized_file = File('resized_img.jpg')
      ..writeAsBytesSync(Img.encodeJpg(resized_img));

    var stream = new http.ByteStream(DelegatingStream.typed(resized_file.openRead()));
    var length = await resized_file.length();

    var uri = Uri.parse("https://myserver.com/upload.php");

    var request = new http.MultipartRequest("POST", uri);
    var multipartFile = new http.MultipartFile('file', stream, length,
        filename: p.basename("resized_image.jpg"));


    request.files.add(multipartFile);
    var response = await request.send();
    print(response.statusCode);
    response.stream.transform(utf8.decoder).listen((value) {
      print(value);
    });
  }

When I run this code, and the app just freezes and the images didn't upload to the server.

[VERBOSE-2:shell.cc(181)] Dart Error: Unhandled exception: FileSystemException: Cannot open file, path = 'thumbnail.jpg' (OS Error: Operation not permitted, errno = 1) #0 _File.throwIfError (dart:io/file_impl.dart:647:7) #1 _File.openSync (dart:io/file_impl.dart:491:5) #2 _File.writeAsBytesSync (dart:io/file_impl.dart:616:31) — Niccolo
– Niccolo, Commented Oct 2, 2018 at 7:52
So the problem is that it cannot open the file called 'thumbnail.jpg'. Is this an asset or an image that was downloaded? Where is it looking for this image? — LarssonK
– LarssonK, Commented Oct 2, 2018 at 9:02
@user7380419 you can't access files in the filesystem like that directly. You have to use the path_provider plugin to write the file in the app's temporary or application directory. In practice though, Richard's answer below is a much better option. — Kirollos Morkos
– Kirollos Morkos, Commented Oct 2, 2018 at 15:02

Richard Heap · Accepted Answer · 2018-10-02 11:20:57Z

12

There's no need to write it to a file; you can send the resized image directly from memory.

uploadImages(File image_File) async {
  img.Image image_temp = img.decodeImage(image_File.readAsBytesSync());
  img.Image resized_img = img.copyResize(image_temp, 800);

  var request = new http.MultipartRequest(
    'POST',
    Uri.parse('https://myserver.com/upload.php'),
  );
  var multipartFile = new http.MultipartFile.fromBytes(
    'file',
    img.encodeJpg(resized_img),
    filename: 'resized_image.jpg',
    contentType: MediaType.parse('image/jpeg'),
  );

  request.files.add(multipartFile);
  var response = await request.send();
  print(response.statusCode);
  response.stream.transform(utf8.decoder).listen((value) {
    print(value);
  });
}

Note: when you import packages, you should use a lower case label (i.e. img). You'll need to import package:http_parser to get MediaType too.

answered Oct 2, 2018 at 11:20

Richard Heap

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2 Comments

Niccolo Over a year ago

Hi, thanks Richard! the function is working good, but it takes 2mins to resize one image, is it normal?

Richard Heap Over a year ago

Yes. The image package runs in pure dart and isn't heavily optimized. Wherever possible, capture the image in lower resolution. See, for example Image size taken from Flutter Image_Picker plugin is way too big

Anand saga · Accepted Answer · 2019-05-20 12:11:01Z

3

While i am using

package:image/image.dart

facing below issues

showing blank page while converting image ( may be taking so much process while compressing image)
After compression image was stretched and not looking good

Then used below plugin, same working fine without any issue, even faster and what i expected

https://github.com/btastic/flutter_native_image.git

steps and method available in above link.

answered May 20, 2019 at 12:11

Anand saga

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