Step-by-Step tutorial to make an Android Application which can scan text from the images that mobile camera shows using Google Vision API

Demo Video of the App that will get formed following the below tutorial.

 

Step 1:- Add the following dependency in module-level build.gradle file,

implementation 'com.google.android.gms:play-services-vision:15.0.2'

Step 2:- Add the meta-data to AndroidManifest.xml,

<meta-data android:name="com.google.android.gms.vision.DEPENDENCIES"

           android:value="orc" />

Step 3:- Add the following permission to AndroidManifest.xml,

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

Step 4:- Design the layout in activity_main.xml,

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    tools:context=".MainActivity"

    android:padding="10dp">



    <SurfaceView

        android:layout_width="match_parent"

        android:layout_height="match_parent"

        android:id="@+id/surface_view"

        />



    <TextView

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:layout_alignParentBottom="true"

        android:text="No Text"

        android:id="@+id/text_view"

        android:textColor="#ffffff"

        android:textSize="20sp"

        android:layout_margin="10dp" />



</RelativeLayout>

Step 5:- Now write the following code in MainActivity.java,

import android.Manifest;

import android.content.pm.PackageManager;

import android.support.annotation.NonNull;

import android.support.v4.app.ActivityCompat;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.util.Log;

import android.util.SparseArray;

import android.view.SurfaceHolder;

import android.view.SurfaceView;

import android.widget.TextView;



import com.google.android.gms.vision.CameraSource;

import com.google.android.gms.vision.Detector;

import com.google.android.gms.vision.text.TextBlock;

import com.google.android.gms.vision.text.TextRecognizer;



import java.io.IOException;



public class MainActivity extends AppCompatActivity {



    SurfaceView cameraView;

    TextView textView;

    CameraSource cameraSource;

    final int RequestCameraPermissionID = 1001;



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);



        cameraView = (SurfaceView) findViewById(R.id.surface_view);

        textView = (TextView) findViewById(R.id.text_view);



        TextRecognizer textRecognizer = new TextRecognizer.Builder(getApplicationContext()).build();



        if (!textRecognizer.isOperational()) {



            Log.d("MainActivity", "Detector Dependencies are not yet available");

        } else {

            cameraSource = new CameraSource.Builder(getApplicationContext(), textRecognizer)

                    .setFacing(CameraSource.CAMERA_FACING_BACK)

                    .setRequestedPreviewSize(1280, 1024)

                    .setRequestedFps(2.0f)

                    .setAutoFocusEnabled(true)

                    .build();



            cameraView.getHolder().addCallback(new SurfaceHolder.Callback() {

                @Override

                public void surfaceCreated(SurfaceHolder holder) {



                    try {

                        if (ActivityCompat.checkSelfPermission(getApplicationContext(), Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {



                            ActivityCompat.requestPermissions(MainActivity.this,

                                    new String[] {android.Manifest.permission.CAMERA},

                                    RequestCameraPermissionID);

                            return;

                        }

                        cameraSource.start(cameraView.getHolder());



                    }

                    catch (IOException e)

                    {

                        e.printStackTrace();

                    }



                }



                @Override

                public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {



                }



                @Override

                public void surfaceDestroyed(SurfaceHolder holder) {



                    cameraSource.stop();



                }

            });



            textRecognizer.setProcessor(new Detector.Processor<TextBlock>() {

                @Override

                public void release() {



                }



                @Override

                public void receiveDetections(Detector.Detections<TextBlock> detections) {



                    final SparseArray<TextBlock> items = detections.getDetectedItems();

                    if(items.size() != 0)

                    {

                        textView.post(new Runnable() {

                            @Override

                            public void run() {

                                StringBuilder stringBuilder = new StringBuilder();



                                for(int i=0;i<items.size();++i) {

                                    TextBlock item = items.valueAt(i);

                                    stringBuilder.append(item.getValue());

                                    stringBuilder.append("\n");

                                }



                                textView.setText(stringBuilder.toString());



                            }

                        });

                    }



                }

            });



        }



    }



    @Override

    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {



        switch(requestCode) {



            case RequestCameraPermissionID:

                if (grantResults[0] == PackageManager.PERMISSION_GRANTED ) {



                    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {



                        return;

                    }

                    try {

                        cameraSource.start(cameraView.getHolder());

                    } catch (IOException e) {

                        e.printStackTrace();

                    }

                }



        }



    }

}