flutter_image_compress

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.

flutter_image_compress

About version

flutter sdk version	plugin version
1.5.9+	use git ref
1.5.8 or low	use pub version

For reasons in this issue

So, in line with the official pub distribution strategy, I will open a branch to track the dev version of Flutter support, and the master version is not supported for the time being due to frequent changes and incompatibilities.

flutter 1.6.0

dependencies:
  flutter_image_compress:
    git:
      url: https://github.com/OpenFlutter/flutter_image_compress.git
      ref: c3c891d0be54f0892bcb4e9c4608d7ad1498e73c

flutter 1.6.3

dependencies:
  flutter_image_compress:
    git:
      url: https://github.com/OpenFlutter/flutter_image_compress.git
      ref: 173ce7d73835ce35f695ac859bdabf471d1160e6

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:

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.

sk3llo / flutter_image_compress Goto Github PK