OpenCV on Android Platforms

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OpenCV on Android Platforms

Marco Moltisanti

Image Processing Lab – http://iplab.dmi.unict.it

[email protected]

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Outline

• Intro

• System setup

• Write and build an Android app

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A couple of words about Android / 1

• Android is a Linux-based OS, oriented to mobile devices;

• Android, Inc. was founded in 2003 by Andy

Rubin, Rich Miner, Nick Sears and Chris White; • Google acquired Android, Inc. in 2005;

• In 2007, Open Handset Alliance, a consortium including Google, HW manufacturers and TC

operators, unveiled Android as its first product, a mobile device platform.

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A couple of words about Android / 2

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A couple of words about Android / 3

• Applications for Android OS can be acquired through an app store, such as Google Play or the Amazon App Store;

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Android Apps / 1

• An Android app is packaged and distributed as an Android Package, i.e. a file with apk

extension. All the code and data in a single apk file is considered a to be one application. • Each app lives in a sandbox inside the

Linux-based Android OS.

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MyApp

Android Apps / 2

A single screen with a user interface Run in

background Manage data

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Android Apps: file Manifest

• The system must know the existence of the application’s components.

• A «manifest» file, named

AndroidManifest.xml, is needed in order to:

– Declare components;

– Identify user permissions (e.g. Internet Access); – Declare minimum API level;

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Android Apps

• An exhaustive view of Application’s

architecture would take too much time… • Further informations available at

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Let’s start!

• First of all, we need to setup our work environment.

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Ingredients

Java SDK 6 or

higher Eclipse IDE

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Recipe / 1

• Download and install Java SDK from

http://www.oracle.com/technetwork/java/jav

ase/downloads/jdk7u9-downloads-1859576.html

• Let JAVA_FOLDER be the folder where we

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Recipe / 2

• Download and install Android SDK from

http://developer.android.com/sdk/index.html

• Download and unzip Android NDK from

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Recipe / 3

• Download and unzip Eclipse IDE for Java Developers from

http://www.eclipse.org/downloads/

• Install the Android Development Tools (ADT) plugin for Eclipse:

http://developer.android.com/sdk/installing/insta lling-adt.html

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Recipe / 4

• A good quick start guide is available at

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Android application structure

Jni C/C++ application source code Control the C++ build process

Android.mk and Application.mk Written with Makefile syntax Libs _{Compiled libs}

Res _{Resources of the application} Images

xml files describing UI layout

Src _{Java code of the application}

AndroidManifest.xml _{essential information about}

application to the Android system:

Name of the Application

Name of main application’s package Components of the application Required permissions

Project root folder

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Hello World! / 1

• Click on the highlighted button (if you don’t

have it, you have to

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Hello World! / 2

• Fill the form and click next.

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Run, Hello World, run! / 1

• To run our HelloWorld! App we have to setup a Virtual Device.

• This can be done using Android Virtual Device Manager, that comes with the SDK.

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Run, Hello World, run! / 2

• From Eclipse, click Run (CTRL+F11) and select the Android App

modality

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A bit deeper… / 1

• The user interface (UI) of an application is stored in a xml file, which contains each component’s settings.

• The UI can be created modifying the xml or using the tools provided by Eclipse.

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A bit deeper… / 2

• The logic part is in a java file, with the same name of the activity we’re working on.

• In our example, it’s in MainActivity.java

• It is possible to access layout elements using the

findViewById method.

• public View findViewById (int id)

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Events Handling

• Nobody likes a static UI!

• Here we use the Java event handling paradigm: Event Listeners!

• Each event has its own listener – onClickListener

– onCheckedChangeListener – …

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OpenCV for Android

There are 3 ways to use OpenCV on Android

1. Basic level

• OpenCV Java API only + Android SDK.

2. Advanced level

• OpenCV native interface + Android NDK.

3. Hacker level

• We don't suggest this way.

• 1 & 2 use prebuilt OpenCV package:

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Basic level

• OpenCV exposes almost all its functionality to Java including camera

• You don't even need to dive into NDK stuff

• You simply add a reference to the OpenCV, import its classes and move forward

• The overhead is equal to a cost of one or several JNI calls

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Advanced level

• The Android way is writing all your code in Java

• Sometimes it is not enough and you need to go to a

native level and write part of your application in C/C++:

– For example: you already have some computer

functionality which is written in C++ but do not want to rewrite the C++ code to Java.

• Add a class with native methods and wrapping your C++ functionality into the Java part of your Android application

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Hacker level

• We don't recommend this way, but it is useful if you want to work with OpenCV sources.

– Implement some new features – Optimize the performance

– Submit a bugfix

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Install OpenCV Manager on the VD / 1

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Install OpenCV Manager on the VD / 2

• Let ANDROID_SDK be the folder where we installed the SDK;

• Let ANDROID_OPENCV be the folder where we put the opencv4android libs;

• Open a shell:

– cd ANDROID_SDK\platform_tools – adb install

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And now?

String code = "Let’s go to write down the code!";