Luban/Translation

Luban

:book: 中文文档

Luban is an image compressing tool for android with efficacy very close to that of WeChat Moments.

Description

With mobile development, showing images in an app has become a very frequent task. But with the ever increasing resolution of smartphone cameras, image compression has become a rather important concern. Although there are already a lot of writings on the internet on the topic, a great number of possible scenarios still have to be though of, like unsuccessful compressions, too small pictures (eg. for profile pictures) or too bad image quality.

Naturally, the first idea was to see how the WeChat, the app giant manages this task in action. To gather data, 100 images with different resolutions were sent through WeChat Moments, then the compressed images were compared with the original ones. Luban's foundation is the result of this analysis on WeChat's compression method. Because the process was analyzed backwards, Luban's efficacy is not yet exactly the same as that of WeChat, but the results are already very close to what WeChat Moments' image compression produces - see the concrete comparison below.

Efficacy with comparison to other tools

Content	Original picture	Luban	Wechat
720P screenshot	720*1280,390k	720*1280,87k	720*1280,56k
1080P screenshot	1080*1920,2.21M	1080*1920,104k	1080*1920,112k
13M photo (4:3)	3096*4128,3.12M	1548*2064,141k	1548*2064,147k
9.6M photo (16:9)	4128*2322,4.64M	1032*581,97k	1032*581,74k
Extended screenshot	1080*6433,1.56M	1080*6433,351k	1080*6433,482k

Setup

compile 'io.reactivex:rxandroid:1.2.1'
compile 'io.reactivex:rxjava:1.1.6'

compile 'top.zibin:Luban:1.0.8'

Usage

Via a Listener

Luban internally uses the IO thread to perform image compression, implementations only need to specify what happens when the process finishes successfully.

Luban.get(this)
    .load(File)                     // pass image to be compressed
    .putGear(Luban.THIRD_GEAR)      // set compression level, defaults to 3
    .setCompressListener(new OnCompressListener() { // Set up return
    
        @Override
        public void onStart() {
            // TODO Called when compression starts, display loading UI here
        }
        @Override
        public void onSuccess(File file) {
            // TODO Called when compression finishes successfully, provides compressed image
        }
        
        @Override
        public void onError(Throwable e) {
            // TODO Called if an error has been encountered while compressing
        }
    }).launch();    // Start compression

With RxJava

With RxJava, more freedom is left to the programmer on controlling the process.

Luban.get(this)
        .load(file)
        .putGear(Luban.THIRD_GEAR)
        .asObservable()
        .subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .doOnError(new Action1<Throwable>() {
            @Override
            public void call(Throwable throwable) {
                throwable.printStackTrace();
            }
        })
        .onErrorResumeNext(new Func1<Throwable, Observable<? extends File>>() {
            @Override
            public Observable<? extends File> call(Throwable throwable) {
                return Observable.empty();
            }
        })
        .subscribe(new Action1<File>() {
            @Override
            public void call(File file) {
                // TODO called when compression finishes successfully, provides compressed image
            }
        });

License

Copyright 2016 Zheng Zibin

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

Translation: Szabolcs Pasztor
Last updated: Aug 8, 2016