flutter_image_compress

ImageCompress pub package GitHub GitHub stars Awesome

Compresses image as native plugin (Obj-C/Kotlin)

This library can works on Android and iOS.

Why

Q:Dart already has image compression libraries. Why use native?

A:For unknown reasons, image compression in Dart language is not efficient, even in release version. Using isolate does not solve the problem.

About version

flutter sdk versionplugin version
1.5.9+use git ref
1.5.8 or low0.5.1

For reasons in this issue, version 0.5.0 is not compatible with pub and cannot be searched on pub. If you want to support flutter 1.6.0 use git ref.

Incompatibility between flutter SDK.

dependencies:
  flutter_image_compress:
    git:
      url: https://github.com/OpenFlutter/flutter_image_compress.git
      ref: 5a545f7e5409d091cd18f5891a8b07426f390729

Breaking change at version 0.5.1

Because #46 and subsequent changes have caused the image Angle to be automatically corrected based on Exif" this default behavior conflicts with the previous argument 'rotate' to rotate the Angle based on Exif information, so I think this is a destructive change.

About params

minWidth and minHeight

minWidth and minHeight are constraints on image scaling.

For example, a 4000*2000 image, minWidth set to 1920, minHeight set to 1080, the calculation is as follows:

// Using dart as an example, the actual implementation is Kotlin or OC.
import 'dart:math' as math;

void main() {
  var scale = calcScale(
    srcWidth: 4000,
    srcHeight: 2000,
    minWidth: 1920,
    minHeight: 1080,
  );

  print("scale = $scale"); // scale = 1.8518518518518519
  print("target width = ${4000 / scale}, height = ${2000 / scale}"); // target width = 2160.0, height = 1080.0
}

double calcScale({
  double srcWidth,
  double srcHeight,
  double minWidth,
  double minHeight,
}) {
  var scaleW = srcWidth / minWidth;
  var scaleH = srcHeight / minHeight;

  var scale = math.max(1.0, math.min(scaleW, scaleH));

  return scale;
}

If your image width is smaller than minWidth or height samller than minHeight, scale will be 1, that is, the size will not change.

autoCorrectionAngle

This property only exists in the version after 0.5.0.

And for historical reasons, there may be conflicts with rotate attributes, which need to be self-corrected.

Modify rotate to 0 or autoCorrectionAngle to false.

Android

You may need to update Kotlin to version 1.2.71(Recommend 1.3.21) or higher.

iOS

No problems currently found.

Usage

dependencies:
  flutter_image_compress: ^0.5.1
import 'package:flutter_image_compress/flutter_image_compress.dart';

Use as:

See full example

  Future<List<int>> testCompressFile(File file) async {
    var result = await FlutterImageCompress.compressWithFile(
      file.absolute.path,
      minWidth: 2300,
      minHeight: 1500,
      quality: 94,
      rotate: 90,
    );
    print(file.lengthSync());
    print(result.length);
    return result;
  }

  Future<File> testCompressAndGetFile(File file, String targetPath) async {
    var result = await FlutterImageCompress.compressAndGetFile(
        file.absolute.path, targetPath,
        quality: 88,
        rotate: 180,
      );

    print(file.lengthSync());
    print(result.lengthSync());

    return result;
  }

  Future<List<int>> testCompressAsset(String assetName) async {
    var list = await FlutterImageCompress.compressAssetImage(
      assetName,
      minHeight: 1920,
      minWidth: 1080,
      quality: 96,
      rotate: 180,
    );

    return list;
  }

  Future<List<int>> testComporessList(List<int> list) async {
    var result = await FlutterImageCompress.compressWithList(
      list,
      minHeight: 1920,
      minWidth: 1080,
      quality: 96,
      rotate: 135,
    );
    print(list.length);
    print(result.length);
    return result;
  }

Result

The result of returning a List collection will not have null, but will always be an empty array.

The returned file may be null. In addition, please decide for yourself whether the file exists.

About List<int> and Uint8List

You may need to convert List<int> to Uint8List to display images.

To use Uint8List, you need import package to your code like so:

img

final image = Uint8List.fromList(imageList)
ImageProvider provider = MemoryImage(Uint8List.fromList(imageList));

Usage in Image Widget:

List<int> image = await testCompressFile(file);
ImageProvider provider = MemoryImage(Uint8List.fromList(image));

Image(
  image: provider ?? AssetImage("img/img.jpg"),
),

Write to file usage:

void writeToFile(List<int> image, String filePath) {
  final file = File(filePath);
  file.writeAsBytes(image, flush: true, mode: FileMode.write);
}

Troubleshooting

Compressing returns null

Sometimes, compressing will return null. You should check if you can read/write the file, and the parent folder of the target file must exist.

For example, use the path_provider plugin to access some application folders, and use a permission plugin to request permission to access SD cards on Android/iOS.

Android build error

Caused by: org.gradle.internal.event.ListenerNotificationException: Failed to notify project evaluation listener.
        at org.gradle.internal.event.AbstractBroadcastDispatch.dispatch(AbstractBroadcastDispatch.java:86)
        ...
Caused by: java.lang.AbstractMethodError
        at org.jetbrains.kotlin.gradle.plugin.KotlinPluginKt.resolveSubpluginArtifacts(KotlinPlugin.kt:776)
        ...

See flutter/flutter/issues#21473

You need to upgrade your Kotlin version to 1.2.71+.

If Flutter supports more platforms (Windows, Mac, Linux, etc) in the future and you use this library, propose an issue or PR!

About EXIF information

Using this library, EXIF information will be removed.

Although it will not be retained, over version 0.5.0, there will be the option of "automatic angle correction", which will be turned on by default.

Libraries

flutter_image_compress