public class MainActivity extends AppCompatActivity implements View.OnClickListener {

private static final String TAG = "MainActivity";
private Button button, buttonCompress;
private String encoded_string, image_name;
private Bitmap bitmap;
private ImageView img;
private File file;
private Uri file_uri;
private ProgressDialog mProgressDialog;
Intent data;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ActivityCompat.requestPermissions(this, new String[]
            {android.Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);//For writing into internal storage.

    img = (ImageView) findViewById(R.id.imageView);
     button = (Button) findViewById(R.id.btnCam);
    buttonCompress = (Button) findViewById(R.id.btnComp);
    button.setOnClickListener(this);
    buttonCompress.setOnClickListener(this);

}

@Override
public void onClick(View view) {
    switch (view.getId()) {
        case R.id.btnCam:
            Intent intentCamera = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
            getFileUri();
            intentCamera.putExtra(MediaStore.EXTRA_OUTPUT, file_uri);
            startActivityForResult(intentCamera, 10);
            break;
        case R.id.btnComp:
            getImageBytes(img);
            getFileUri();
            break;
    }

}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {

    if (requestCode == 10 && resultCode == RESULT_OK) {
        img.setImageURI(file_uri);
        Log.d("path is", file.getPath());
        Toast.makeText(MainActivity.this, "Successfully Written !!", Toast.LENGTH_SHORT).show();
    }
}

private void getFileUri() {
    image_name = "picture1.jpg";
    file = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES)
            + File.separator + image_name
    );
    file_uri = Uri.fromFile(file);
    Log.d("uri is", file_uri.toString());
}


private byte[] getImageBytes(@NonNull ImageView imageView) {
    Bitmap bitmap = ((BitmapDrawable) imageView.getDrawable()).getBitmap();
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    bitmap.compress(Bitmap.CompressFormat.JPEG, 50, bos);
    return bos.toByteArray();
}

<ImageView
    android:id="@+id/imageView"
    android:layout_width="257dp"
    android:layout_height="300dp"
    app:srcCompat="@mipmap/ic_launcher"
    tools:layout_editor_absoluteX="32dp"
    tools:layout_editor_absoluteY="98dp"
    android:adjustViewBounds="true"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true" />

<Button
    android:id="@+id/btnCam"
    android:layout_width="94dp"
    android:layout_height="36dp"
    android:text="Camera"
    tools:layout_editor_absoluteY="448dp"
    tools:layout_editor_absoluteX="145dp"
    android:layout_marginLeft="31dp"
    android:layout_marginStart="31dp"
    android:layout_below="@+id/imageView"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:layout_marginTop="60dp" />

<Button
    android:id="@+id/btnComp"
    android:layout_width="76dp"
    android:layout_height="41dp"
    android:text="compress"
    tools:layout_editor_absoluteX="-9dp"
    tools:layout_editor_absoluteY="-5dp"
    android:layout_alignBottom="@+id/btnCam"
    android:layout_alignRight="@+id/imageView"
    android:layout_alignEnd="@+id/imageView" />