Face Detection in Android

by durga chiranjeevi 9/05/2014 | 6:56 0 Posted in Android

In this blog post, I would like explain how to detect the faces in the photograph.

The application will detect the number of faces in the image and draws a rectangle around each face in the image. To do face detection we use android.media.FaceDetector class which identifies the location of the face in a bitmap.

So lets Start: 1. Create a new project File -> Android Project. While creating a new project give activity name as AndroidFaceDetection(AndroidFaceDetection.java) and copy this code:

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;

import android.app.Activity;
import android.content.ContentValues;
import android.content.Intent;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PointF;
import android.media.FaceDetector;
import android.media.FaceDetector.Face;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

public class AndroidFaceDetection extends Activity {
 private static final int SELECT_GALLERY_CODE = 1;
 private static final int TAKE_PICTURE_CODE = 2;

 Button bTakePic, bSelectPic;
 static ImageView imgView;
 // private MyImageView imgView;
 public int imageWidth;
 public int imageHeight;
 public int numberOfFace = 5;
 public FaceDetector myFaceDetect;
 public FaceDetector.Face[] myFace;
 float myEyesDistance;
 int numberOfFaceDetected;
 Bitmap mFaceBitmap;
 InputStream stream;
 int[] fpx = null;
 int[] fpy = null;
 Canvas canvas = new Canvas();
 Paint myPaint = new Paint();
 ContentValues values;
 Uri imageUri;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
 // TODO Auto-generated method stub
 super.onCreate(savedInstanceState);
 setContentView(R.layout.main);
 bTakePic = (Button) findViewById(R.id.takePicture);
 bSelectPic = (Button) findViewById(R.id.selectPicture);
 imgView = (ImageView) findViewById(R.id.imageView1);

 bSelectPic.setOnClickListener(new View.OnClickListener() {

 @Override
 public void onClick(View v) {
 // TODO Auto-generated method stub
 Intent intent = new Intent();
 intent.setType("image/*");
 intent.setAction(Intent.ACTION_GET_CONTENT);
 intent.addCategory(Intent.CATEGORY_OPENABLE);
 startActivityForResult(intent, SELECT_GALLERY_CODE);
 }
 });
 bTakePic.setOnClickListener(new View.OnClickListener() {

 @Override
 public void onClick(View v) {
 // TODO Auto-generated method stub
 values = new ContentValues();
 values.put(MediaStore.Images.Media.TITLE, "New Picture");
 values.put(MediaStore.Images.Media.DESCRIPTION, "From your Camera");
 imageUri = getContentResolver().insert(
 MediaStore.Images.Media.EXTERNAL_CONTENT_URI, values);
 Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
 intent.putExtra(MediaStore.EXTRA_OUTPUT, imageUri);
 
 startActivityForResult(intent, TAKE_PICTURE_CODE);
 }
 });

 }

 @Override
 protected void onActivityResult(int requestCode, int resultCode, Intent data) {
 if (requestCode == SELECT_GALLERY_CODE
 && resultCode == Activity.RESULT_OK) {
 try {
 // We need to recyle unused bitmaps
 if (mFaceBitmap != null) {
 mFaceBitmap.recycle();
 }

 stream = getContentResolver().openInputStream(data.getData());
 Bitmap b = BitmapFactory.decodeStream(stream);

 mFaceBitmap = b.copy(Bitmap.Config.RGB_565, true);
 b.recycle();
 imgView.setImageBitmap(mFaceBitmap);
 DetectFaces();
 stream.close();

 } catch (FileNotFoundException e) {
 e.printStackTrace();
 } catch (IOException e) {
 e.printStackTrace();
 }
 } else if (TAKE_PICTURE_CODE == requestCode) 
 if (resultCode == Activity.RESULT_OK) {

 try {
 Bitmap b = MediaStore.Images.Media.getBitmap(
 getContentResolver(), imageUri);
 mFaceBitmap = b.copy(Bitmap.Config.RGB_565, true);
 b.recycle();
 imgView.setImageBitmap(mFaceBitmap);
 DetectFaces();
 } catch (Exception e) {
 e.printStackTrace();
 }

 }
 super.onActivityResult(requestCode, resultCode, data);
 }
 

 public void DetectFaces() {
 // TODO Auto-generated method stub

 imageWidth = mFaceBitmap.getWidth();
 imageHeight = mFaceBitmap.getHeight();
 imgView.setImageBitmap(mFaceBitmap);

 myFace = new FaceDetector.Face[numberOfFace];
 myFaceDetect = new FaceDetector(imageWidth, imageHeight, numberOfFace);
 numberOfFaceDetected = myFaceDetect.findFaces(mFaceBitmap, myFace);
 Toast.makeText(AndroidFaceDetection.this, "No of Face Detected: "+numberOfFaceDetected, Toast.LENGTH_LONG).show();
 Paint ditherPaint = new Paint();
 ditherPaint.setDither(true);

 myPaint.setColor(Color.GREEN);
 myPaint.setStyle(Paint.Style.STROKE);
 myPaint.setStrokeWidth(3);

 canvas.setBitmap(mFaceBitmap);
 canvas.drawBitmap(mFaceBitmap, 0, 0, ditherPaint);

 if (numberOfFaceDetected > 0) {
 for (int i = 0; i < numberOfFaceDetected; i++) {
 Face face = myFace[i];
 PointF myMidPoint = new PointF();
 face.getMidPoint(myMidPoint);
 myEyesDistance = face.eyesDistance();

 canvas.drawRect((int) (myMidPoint.x - myEyesDistance * 2),
 (int) (myMidPoint.y - myEyesDistance * 2),
 (int) (myMidPoint.x + myEyesDistance * 2),
 (int) (myMidPoint.y + myEyesDistance * 2), myPaint);

 }

 }

}
 
}

2. Now open your main.xml layout and copy this code:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:id="@+id/ll1"
 android:orientation="vertical" >

 <LinearLayout
 android:layout_width="match_parent"
 android:layout_height="wrap_content" >

 <Button
 android:id="@+id/selectPicture"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:text="Select picture" />

 <Button
 android:id="@+id/takePicture"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:text="Take Picture" />

 </LinearLayout>

 <LinearLayout
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:orientation="vertical" >

 <ImageView
 android:id="@+id/imageView1"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:contentDescription="TODO"
 android:src="@drawable/ic_launcher" />

 </LinearLayout>
 
</LinearLayout>

3. Now add these permissions in your AndroidManifest.xml file:

<uses-feature android:name="android.hardware.camera" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

Tips to Remember always:
1) In this example i’m detecting only 5 faces. If you need to detect more faces, then change this line according to your needs.(On line no: 33)

public int numberOfFace = 5;

2) While accessing camera via Intent, you need to remember that these two line of code snippet is far enough to call a camera, but it returns always the thumbnail of the picture rather than original image.

Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
startActivityForResult(intent, TAKE_PICTURE_CODE);

3) FaceDetector.Face is the Android API. A Face contains all the information identifying the location of a face in a bitmap. (On line no: 140)

4) findfaces() is a method – Finds all the faces found in a given bitmap. (On line no: 142)

5) face.getMidPoint() – Sets the position of the mid-point between the eyes.(On line no: 158)

6) eyedistance() – Returns the distance between the eyes.(On line no: 159)

7) To draw a rectangle around the face, i used


canvas.drawRect((int) (myMidPoint.x - myEyesDistance * 2),
(int) (myMidPoint.y - myEyesDistance * 2),
(int) (myMidPoint.x + myEyesDistance * 2),
(int) (myMidPoint.y + myEyesDistance * 2), myPaint);

I just multiplied into two to grab the whole face rather than marking on a face. But to draw a rectangle on the face, then remove all (*2) from the above code.


canvas.drawRect((int) (myMidPoint.x - myEyesDistance ),
(int) (myMidPoint.y - myEyesDistance ),
(int) (myMidPoint.x + myEyesDistance ),
(int) (myMidPoint.y + myEyesDistance ), myPaint);

Hope this helpful. Your valuable comments are always welcomed. It will help to improve my post and understanding.