@Override
public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.grid_2);
  GridView g = (GridView) findViewById(R.id.myGrid);
  g.setAdapter(new ImageAdapter(this));
} 

public class ImageAdapter extends BaseAdapter {
  public ImageAdapter(Context c) {
    mContext = c;
  }
  public int getCount() {
    return mThumbIds.length;
  }
  public Object getItem(int position) {
    return position;
  }
  public long getItemId(int position) {
    return position;
  }
  public View getView(int position, View convertView, ViewGroup parent) {
    ImageView imageView;
    if (convertView == null) {
      imageView = new ImageView(mContext);
      imageView.setLayoutParams(new GridView.LayoutParams(45, 45));//设置ImageView宽高
      imageView.setAdjustViewBounds(false);
      imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
      imageView.setPadding(8, 8, 8, 8);
    } else {
      imageView = (ImageView) convertView;
    }
    imageView.setImageResource(mThumbIds[position]);
    return imageView;
  }
  private Context mContext;
  private Integer[] mThumbIds = {
      R.drawable.sample_thumb_0, R.drawable.sample_thumb_1,
      R.drawable.sample_thumb_2, R.drawable.sample_thumb_3,
      R.drawable.sample_thumb_4, R.drawable.sample_thumb_5,
      R.drawable.sample_thumb_6, R.drawable.sample_thumb_7
  };
}

<?xml version="1.0" encoding="utf-8"?>
<GridView xmlns:android="http://schemas.android.com/apk/res/android"
  android:id="@+id/myGrid"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:padding="10dp"
  android:verticalSpacing="10dp"
  android:horizontalSpacing="10dp"
  android:numColumns="auto_fit"
  android:columnWidth="60dp"
  android:stretchMode="columnWidth"
  android:gravity="center"
  />

//获得Bitmap的高和宽
int bmpWidth=bmp.getWidth();
int bmpHeight=bmp.getHeight();
//设置缩小比例
double scale=0.8;
//计算出这次要缩小的比例
scaleWidth=(float)(scaleWidth*scale);
scaleHeight=(float)(scaleHeight*scale);
//产生resize后的Bitmap对象
Matrix matrix=new Matrix();
matrix.postScale(scaleWidth, scaleHeight);
Bitmap resizeBmp=Bitmap.createBitmap(bmp, 0, 0, bmpWidth, bmpHeight, matrix, true);

<ImageView
  android:id="@+id/image"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:scaleType="center"
  android:src="@drawable/candle"
  />