Why I cannot see some part of image in fullscreen in viewpager?

I have developed an app which can show image located in drawable folder to the viewer. However, When image is displayed in full screen some part of the image doesn't appear. How can I fix that ? Following are my codes..

MainActivity.java

import android.app.Activity;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.support.v4.view.ViewPager;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ShareActionProvider;




public class MainActivity extends Activity {

    MediaPlayer oursong;

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
      oursong = MediaPlayer.create(MainActivity.this, R.raw.a);
      oursong.start ();
    ViewPager viewPager = (ViewPager) findViewById(R.id.view_pager);
    ImageAdapter adapter = new ImageAdapter(this);
    viewPager.setAdapter(adapter);
  }

  private ShareActionProvider mShareActionProvider;


  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
      // Inflate menu resource file.
      getMenuInflater().inflate(R.menu.activity_main, menu);

      // Locate MenuItem with ShareActionProvider
      MenuItem item = menu.findItem(R.id.menu_item_share);

      // Fetch and store ShareActionProvider
      mShareActionProvider = (ShareActionProvider) item.getActionProvider();

      // Return true to display menu
      return true;
  }

  // Call to update the share intent
  private void setShareIntent(Intent shareIntent) {
      if (mShareActionProvider != null) {
          mShareActionProvider.setShareIntent(shareIntent);
      }
  }

     @Override
     protected void onPause(){
     super.onPause();
      oursong.release();
 }

}

Imageadapter.java

import android.content.Context;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;

public class ImageAdapter extends PagerAdapter {
    Context context;
    private int[] GalImages = new int[] {
        R.drawable.one,
        R.drawable.two,
        R.drawable.three
    };
    ImageAdapter(Context context){
        this.context=context;
    }
    @Override
    public int getCount() {
      return GalImages.length;
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
      return view == ((ImageView) object);
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
      ImageView imageView = new ImageView(context);
      int padding = context.getResources().getDimensionPixelSize(R.dimen.padding_small);
      imageView.setPadding(padding, padding, padding, padding);
      imageView.setScaleType(ImageView.ScaleType.CENTER_CROP  );
      imageView.setImageResource(GalImages[position]);
      ((ViewPager) container).addView(imageView, 0);
      return imageView;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
      ((ViewPager) container).removeView((ImageView) object);
    }
  }

dimens.xml

<resources>
  <dimen name="padding_small">4dp</dimen>
  <dimen name="padding_medium">8dp</dimen>
  <dimen name="padding_large">16dp</dimen>
</resources>

I just start with programming, so please give some explanations, or it will be great if you also give some codes...