Android Application Programming with OpenCV: For Java developers OpenCV is a fantastic opportunity to benefit from the popularity of image related mobile apps on Android. This book teaches you all you need to know about computer vision with practical projects.

Let's make an app that enables people to see new visual patterns, to animate and interact with these patterns, and to share them as pictures. The idea is simple and versatile. Anyone, from a child to a computer vision expert, can appreciate the patterns. Through the magic of computer vision on a mobile device, any user can more readily see, change, and share hidden patterns in any scene.

For this app, I chose the name Second Sight, a phrase that is sometimes used in mythology to refer to supernatural and symbolic visions.

At its core, Second Sight is a camera app. It will enable the user to preview, save, and share photos. Like many other camera apps, it will also let the user to apply filters to the preview and the saved photos. However, many of the filters will not be traditional photographic effects. For example, the more complex filters will enable the user to see stylized edges or even rendered objects that blend with the real scene (augmented reality...

We need to create a new Eclipse project for our app. We may do this in the same workspace that we already used for the OpenCV library project and samples. Alternatively, if we use another workspace, we must import the OpenCV library project into this workspace too. (For instructions on setting the workspace and importing the library project, see the Building the OpenCV samples with Eclipse section of Chapter 1, Setting Up OpenCV.)

Open Eclipse to a workspace that contains the library project. Then, from the menu system, navigate to File | New | Android Application Project. The New Android Application window should appear. Enter the options that are shown in the following screenshot:

The Target SDK and Compile With fields should be set to API 11 (Android 3.0) or higher. It is safe to choose the most recent API version, which, at the time of writing, is API 17: Android 4.2 (Jelly Bean). The Minimum Required SDK field should be left at the default, API 8: Android...

The AndroidManifest.xml (the manifest) file specifies an Android app's requirements and components. Compared to the default manifest, the manifest in Second Sight needs to do the following additional work:

We can accomplish these tasks by editing the uses-permission, uses-feature, and activity tags in the...

Our app's menus and localizable text are described in XML files. Identifiers in these resource files are referenced by Java code, as we will see later.

First, let's edit res/menu/activity_camera.xml so that it has the following implementation, describing the menu items for CameraActivity:

<menu xmlns:android="http://schemas.android.com/apk/res/android" >
  <item
    android:id="@+id/menu_next_camera"
    android:orderInCategory="100"
    android:showAsAction="ifRoom|withText"
    android:title="@string/menu_next_camera"/>
  <item
    android:id="@+id/menu_take_photo"
    android:orderInCategory="100"
    android:showAsAction="always|withText"
    android:title="@string/menu_take_photo"/>
</menu>

Note that we use the android:showAsAction attribute to make menu items appear in the app's top bar...

Our main activity, CameraActivity, needs to do the following:

We will use OpenCV functionality wherever feasible, even though we could just use the standard Android libraries to display a live camera feed, save a photo, and so on.

OpenCV provides an abstract class called CameraBridgeViewBase, which represents a live camera feed. This class extends Android's SurfaceView class, so that its instances can be part of the view hierarchy. Moreover, a...

Our second activity, LabActivity, needs to do the following:

All of this functionality relies on standard Android library classes, notably the Intent class. Intents are the means by which activities communicate with each other. An activity receives an intent from its parent (the activity that created it) and may receive intents from its children (activities it created) as they finish. The communicating activities may be in different applications. An intent may...

We have used OpenCV to create and show a live camera feed, and to save still images from this feed. We have also seen how to integrate the camera feed's lifecycle into the Android activity lifecycle, and how to share saved images across the boundaries of activities and applications.

The next chapter will expand our Second Sight app by adding various image filtering options to the menus of CameraActivity and LabActivity.