Face Detection In Xamarin.Android

Firstly, we can create our main layout having a button to take picture using camera and name it the following:

Main.axml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="match_parent"
    android:padding="10dip">
    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Click Take a Picture button"
        android:gravity="center_horizontal"
        android:layout_weight="1.0" />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/take_picture"
        android:layout_margin="5dip"
        android:text="Take Picture"
        android:layout_gravity="center_horizontal" />
</LinearLayout>

Now we need a layout named detectlayout.axml having a ImageView to display the picture which we had captured using camera and a Button to detect faces in that Image.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <ImageView
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:id="@+id/image_view"
        android:layout_weight="1.0"
        android:src="@android:drawable/ic_menu_report_image" />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/detect_face"
        android:text="Detect Face"
        android:layout_gravity="center_horizontal" />
</LinearLayout>

Now let's start coding.

Firstly, we want to open an activity to take picture.

private void openCamera()
{
   Intent intent = new Intent (Android.Provider.MediaStore.ActionImageCapture);
   StartActivityForResult (intent, TAKE_PICTURE_CODE);
}

Now we want to Process the captured picture and display it on the detectlayout.axml.

private void processCameraImage(Intent intent)
{
    //Change layout to main Layout
    SetContentView(Resource.Layout.detectlayout);

    Button detect_face = FindViewById<Button> (Resource.Id.detect_face);

    detect_face.Click += detect_face_Clicked;

    ImageView image_view = FindViewById<ImageView> (Resource.Id.image_view);

    //Set image
    image_view.SetImageBitmap(cameraBitmap);
}

Add our main ingredient, here we detecting the faces on the picture and drawing a square to mark those faces.

private void detectFaces(){
    //first check if picture has been taken
    if(null != cameraBitmap){
        //get width of a picture
        int width = cameraBitmap.Width;
        //get height of a picture
        int height = cameraBitmap.Height;
        //Initialize a facedetector with the picture dimensions and the max number of faces to check
        FaceDetector detector = new FaceDetector(width, height, MainActivity.MAX_FACES);
        //Create an array of faces with the number of max faces to check
        FaceDetector.Face[] faces = new FaceDetector.Face[MainActivity.MAX_FACES];

        //create a main bitmap
        Bitmap bitmap565 = Bitmap.CreateBitmap(width, height, Bitmap.Config.Rgb565);
        //create a dither paint
        Paint ditherPaint = new Paint();
        //create a draw paint
        Paint drawPaint = new Paint();

        //set true dither to dither paint variable
        ditherPaint.Dither = true;
        //set color red for the square
        drawPaint.Color = Color.Green;
        //set stroke to style
        drawPaint.SetStyle(Paint.Style.Stroke);
        //set stroke width
        drawPaint.StrokeWidth = 2;

        //Create a canvas
        Canvas canvas = new Canvas();
        //set bitmap to canvas
        canvas.SetBitmap(bitmap565);
        //draw bitmap to canvas
        canvas.DrawBitmap(cameraBitmap, 0, 0, ditherPaint);

        //get a number of faces detected
        int facesFound = detector.FindFaces(bitmap565, faces);
        //mid face point
        PointF midPoint = new PointF();
        //eye distance variable
        float eyeDistance = 0.0f;
        //confidence variable
        float confidence = 0.0f;
        //print numbre of faces found
        System.Console.WriteLine ("Number of faces found: " + facesFound);

        //check if found at least one face
        if(facesFound > 0)
        {
            //for each face draw a red squeare
            for(int index=0; index<facesFound; ++index){
                // get midpoint of a face
                faces[index].GetMidPoint(midPoint);
                //get eye distance
                eyeDistance = faces[index].EyesDistance();
                //get confidence
                confidence = faces [index].Confidence ();
                //print all parameters
                System.Console.WriteLine ("Confidence: " + confidence +
                    ", Eye distance: " + eyeDistance +
                    ", Mid Point: (" + midPoint.X + ", " + midPoint.Y + ")");
                //draw a square in the picture
                canvas.DrawRect((int)midPoint.X - eyeDistance ,
                    (int)midPoint.Y- eyeDistance ,
                    (int)midPoint.X + eyeDistance,
                    (int)midPoint.Y + eyeDistance, drawPaint);
            }
        }

        //get imageview from layout
        ImageView imageView = (ImageView)FindViewById(Resource.Id.image_view);
        //set image with the red squares to imageview
        imageView.SetImageBitmap(bitmap565);
    }
}

Now the stage is set for the show, only we need to do is just rearrange the code together in a logical way.

Go through the attachment for the complete project.