Gets the distances from the camera to the focus point - getFocusDistances()

The method getFocusDistances(float[] output) of android.hardware.Camera.Parameters gets the distances from the camera to where an object appears to be in focus. The object is sharpest at the optimal focus distance. The depth of field is the far focus distance minus near focus distance. ~ Since: API Level 9.

Modify AndroidCamera.java from last exercise "java.lang.RuntimeException: autoFocus failed", call getFocusDistances() in onAutoFocus() of myAutoFocusCallback, when focused.

package com.exercise.AndroidCamera;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

import android.app.Activity;
import android.content.ContentValues;
import android.content.Context;
import android.content.pm.ActivityInfo;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
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.Parameters;
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;

DrawingView drawingView;
Face[] detectedFaces;

final int RESULT_SAVEIMAGE = 0;

private ScheduledExecutorService myScheduledExecutorService;

/** 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);

drawingView = new DrawingView(this);
LayoutParams layoutParamsDrawing 
= new LayoutParams(LayoutParams.FILL_PARENT, 
LayoutParams.FILL_PARENT);
this.addContentView(drawingView, layoutParamsDrawing);

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 tcamera) {

if (faces.length == 0){
//prompt.setText(" No Face Detected! ");
drawingView.setHaveFace(false);
}else{
//prompt.setText(String.valueOf(faces.length) + " Face Detected :) ");
drawingView.setHaveFace(true);
detectedFaces = faces;

//Set the FocusAreas using the first detected face
List<Camera.Area> focusList = new ArrayList<Camera.Area>();
Camera.Area firstFace = new Camera.Area(faces[0].rect, 1000);
focusList.add(firstFace);

if(camera.getParameters().getMaxNumFocusAreas()>0){
camera.getParameters().setFocusAreas(focusList);
}

if(camera.getParameters().getMaxNumMeteringAreas()>0){
camera.getParameters().setMeteringAreas(focusList);
}

buttonTakePicture.setEnabled(false);
//camera.getParameters().setFocusMode(Camera.Parameters.FOCUS_MODE_CONTINUOUS_PICTURE);

//Stop further Face Detection
camera.stopFaceDetection();

buttonTakePicture.setEnabled(false);

/*
* Allways throw java.lang.RuntimeException: autoFocus failed 
* if I call autoFocus(myAutoFocusCallback) here!
* 
camera.autoFocus(myAutoFocusCallback);
*/

//Delay call autoFocus(myAutoFocusCallback)
myScheduledExecutorService = Executors.newScheduledThreadPool(1);
myScheduledExecutorService.schedule(new Runnable(){
public void run() {
camera.autoFocus(myAutoFocusCallback);
}
}, 500, TimeUnit.MILLISECONDS);

}

drawingView.invalidate();

}};

AutoFocusCallback myAutoFocusCallback = new AutoFocusCallback(){

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

float focusDistances[] = new float[3];
arg1.getParameters().getFocusDistances(focusDistances);
prompt.setText("Optimal Focus Distance(meters): " 
+ focusDistances[Camera.Parameters.FOCUS_DISTANCE_OPTIMAL_INDEX]);

}};

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;
}

private class DrawingView extends View{

boolean haveFace;
Paint drawingPaint;

public DrawingView(Context context) {
super(context);
haveFace = false;
drawingPaint = new Paint();
drawingPaint.setColor(Color.GREEN);
drawingPaint.setStyle(Paint.Style.STROKE); 
drawingPaint.setStrokeWidth(2);
}

public void setHaveFace(boolean h){
haveFace = h;
}

@Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
if(haveFace){

// Camera driver coordinates range from (-1000, -1000) to (1000, 1000).
// UI coordinates range from (0, 0) to (width, height).

int vWidth = getWidth();
int vHeight = getHeight();

for(int i=0; i<detectedFaces.length; i++){

if(i == 0){
drawingPaint.setColor(Color.GREEN);
}else{
drawingPaint.setColor(Color.RED);
}

int l = detectedFaces[i].rect.left;
int t = detectedFaces[i].rect.top;
int r = detectedFaces[i].rect.right;
int b = detectedFaces[i].rect.bottom;
int left = (l+1000) * vWidth/2000;
int top  = (t+1000) * vHeight/2000;
int right = (r+1000) * vWidth/2000;
int bottom = (b+1000) * vHeight/2000;
canvas.drawRect(
left, top, right, bottom,  
drawingPaint);
}
}else{
canvas.drawColor(Color.TRANSPARENT);
}
}

}
}

Download the files.

Note:
- Set Camera.Parameters

Related:
- Touch to select focus and metering area