Face detection for Camera

Long long time ago(2010-05-19), I have a post "Android FaceDetector" about how to use android.media.FaceDetector to identify faces in a Bitmap.

Start from Android 4, API Level 14, the android.hardware.Camera class provide the feature of Face Detection. You can build apps to detect face on camera at live.



The method startFaceDetection() starts the face detection. This should be called after preview is started. The camera will notify Camera.FaceDetectionListener of the detected faces in the preview frame. The detected faces may be the same as the previous ones. Applications should call stopFaceDetection() to stop the face detection. This method is supported if getMaxNumDetectedFaces() returns a number larger than 0. If the face detection has started, apps should not call this again.

When the face detection is running, setWhiteBalance(String), setFocusAreas(List), and setMeteringAreas(List) have no effect. The camera uses the detected faces to do auto-white balance, auto exposure, and autofocus.

If the apps call autoFocus(AutoFocusCallback), the camera will stop sending face callbacks. The last face callback indicates the areas used to do autofocus. After focus completes, face detection will resume sending face callbacks. If the apps call cancelAutoFocus(), the face callbacks will also resume.

After calling takePicture(Camera.ShutterCallback, Camera.PictureCallback, Camera.PictureCallback) or stopPreview(), and then resuming preview with startPreview(), the apps should call this method again to resume face detection.

It's modify from the exercise "Start Camera auto-focusing, autoFocus()" to add function of face detection.

Modify main.xml to add a SurfaceView for camera preview, and a TextView to display the number of face detected.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >

<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello" />
<TextView
android:id="@+id/prompt"
android:layout_width="fill_parent"
android:layout_height="wrap_content"/>
<SurfaceView
android:id="@+id/camerapreview" 
android:layout_width="fill_parent"
android:layout_height="wrap_content" />

</LinearLayout>

Create /res/layout/control.xml, it's a view overlap with the preview SurfaceView, to provide a button to take picture.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/background"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="bottom"
>
<Button
android:id="@+id/takepicture" 
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text=" * Take Picture "
android:layout_gravity="right"
android:layout_margin="10px"
/>
</LinearLayout>

Main code, call camera.startFaceDetection() after camera.startPreview(), and call camera.stopFaceDetection() before camera.stopPreview(), also define our FaceDetectionListener to display the result of number of face detected.

package com.exercise.AndroidCamera;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.OutputStream;

import android.app.Activity;
import android.content.ContentValues;
import android.content.pm.ActivityInfo;
import android.graphics.PixelFormat;
import android.hardware.Camera;
import android.hardware.Camera.AutoFocusCallback;
import android.hardware.Camera.Face;
import android.hardware.Camera.FaceDetectionListener;
import android.hardware.Camera.PictureCallback;
import android.hardware.Camera.ShutterCallback;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore.Images.Media;
import android.view.LayoutInflater;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.view.ViewGroup.LayoutParams;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.TextView;

public class AndroidCamera extends Activity implements SurfaceHolder.Callback{

Camera camera;
SurfaceView surfaceView;
SurfaceHolder surfaceHolder;
boolean previewing = false;
LayoutInflater controlInflater = null;

Button buttonTakePicture;
TextView prompt;

final int RESULT_SAVEIMAGE = 0;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);

getWindow().setFormat(PixelFormat.UNKNOWN);
surfaceView = (SurfaceView)findViewById(R.id.camerapreview);
surfaceHolder = surfaceView.getHolder();
surfaceHolder.addCallback(this);
surfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);

controlInflater = LayoutInflater.from(getBaseContext());
View viewControl = controlInflater.inflate(R.layout.control, null);
LayoutParams layoutParamsControl
= new LayoutParams(LayoutParams.FILL_PARENT,
LayoutParams.FILL_PARENT);
this.addContentView(viewControl, layoutParamsControl);

buttonTakePicture = (Button)findViewById(R.id.takepicture);
buttonTakePicture.setOnClickListener(new Button.OnClickListener(){

@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
camera.takePicture(myShutterCallback,
myPictureCallback_RAW, myPictureCallback_JPG);
}});

LinearLayout layoutBackground = (LinearLayout)findViewById(R.id.background);
layoutBackground.setOnClickListener(new LinearLayout.OnClickListener(){

@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub

buttonTakePicture.setEnabled(false);
camera.autoFocus(myAutoFocusCallback);
}});

prompt = (TextView)findViewById(R.id.prompt);
}

FaceDetectionListener faceDetectionListener
= new FaceDetectionListener(){

@Override
public void onFaceDetection(Face[] faces, Camera camera) {

if (faces.length == 0){
prompt.setText(" No Face Detected! ");
}else{
prompt.setText(String.valueOf(faces.length) + " Face Detected :) ");
}


}};

AutoFocusCallback myAutoFocusCallback = new AutoFocusCallback(){

@Override
public void onAutoFocus(boolean arg0, Camera arg1) {
// TODO Auto-generated method stub
buttonTakePicture.setEnabled(true);
}};

ShutterCallback myShutterCallback = new ShutterCallback(){

@Override
public void onShutter() {
// TODO Auto-generated method stub

}};

PictureCallback myPictureCallback_RAW = new PictureCallback(){

@Override
public void onPictureTaken(byte[] arg0, Camera arg1) {
// TODO Auto-generated method stub

}};

PictureCallback myPictureCallback_JPG = new PictureCallback(){

@Override
public void onPictureTaken(byte[] arg0, Camera arg1) {
// TODO Auto-generated method stub
/*Bitmap bitmapPicture
= BitmapFactory.decodeByteArray(arg0, 0, arg0.length); */

Uri uriTarget = getContentResolver().insert(Media.EXTERNAL_CONTENT_URI, new ContentValues());

OutputStream imageFileOS;
try {
imageFileOS = getContentResolver().openOutputStream(uriTarget);
imageFileOS.write(arg0);
imageFileOS.flush();
imageFileOS.close();

prompt.setText("Image saved: " + uriTarget.toString());

} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}


camera.startPreview();
camera.startFaceDetection();
}};

@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
// TODO Auto-generated method stub
if(previewing){
camera.stopFaceDetection();
camera.stopPreview();
previewing = false;
}

if (camera != null){
try {
camera.setPreviewDisplay(surfaceHolder);
camera.startPreview();

prompt.setText(String.valueOf(
"Max Face: " + camera.getParameters().getMaxNumDetectedFaces()));
camera.startFaceDetection();
previewing = true;
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

@Override
public void surfaceCreated(SurfaceHolder holder) {
// TODO Auto-generated method stub
camera = Camera.open();
camera.setFaceDetectionListener(faceDetectionListener);
}

@Override
public void surfaceDestroyed(SurfaceHolder holder) {
// TODO Auto-generated method stub
camera.stopFaceDetection();
camera.stopPreview();
camera.release();
camera = null;
previewing = false;
}
}

Modify AndroidManifest.xml, to add permission of "android.permission.CAMERA", and set android:minSdkVersion="14".

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.exercise.AndroidCamera"
android:versionCode="1"
android:versionName="1.0" >

<uses-sdk android:minSdkVersion="14" />
<uses-permission android:name="android.permission.CAMERA"/>

<application
android:icon="@drawable/ic_launcher"
android:label="@string/app_name" >
<activity
android:name=".AndroidCamera"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>

</manifest>

Download the files.

Please note, it's a in-complete exercise. It simple display the number of face detected.

Next: - Android 4 Face Detection: Display detected face area