ZoomControls控件是一个可以缩放控件，可以实现两个按钮控制图片的大小

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/layout"
    >
    <ImageView
        android:id="@+id/image"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/foot"
        />

    <ZoomControls
        android:id="@+id/zoomcontrol"
        android:layout_gravity="bottom"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        />
</LinearLayout>

package com.example.yanlei.my;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.os.Bundle;
import android.app.Activity;
import android.widget.Toast;
import android.view.Menu;
import android.view.MenuItem;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.ZoomControls;

public class MainActivity extends AppCompatActivity {

    private LinearLayout llLayout;
    private ZoomControls zoomcontrols;
    private ImageView img;
    private int id = 0;
    private int displayWidth;
    private int displayHeight;
    private float scaleWidth = 1;
    private float scaleHeight = 1;
    private Bitmap bitmap;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        llLayout = (LinearLayout) findViewById(R.id.layout);
        //取得屏幕分辨率大小
        DisplayMetrics dm = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(dm);
        displayWidth = dm.widthPixels;
        //屏幕高度减去zoomControls的高度
        displayHeight = dm.heightPixels;
        bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.foot);
        img = (ImageView) findViewById(R.id.image);
        //zoom.hide();隐藏zoomControls
        //zoom.show();显示zoomCOntrols

        zoomcontrols = (ZoomControls) findViewById(R.id.zoomcontrol);
        img = (ImageView) findViewById(R.id.image);
        zoomcontrols.setIsZoomInEnabled(true);
        zoomcontrols.setIsZoomOutEnabled(true);
        //图片放大
        zoomcontrols.setOnZoomInClickListener(new OnClickListener() {
            public void onClick(View v) {
                int bmpWidth = bitmap.getWidth();
                int bmpHeight = bitmap.getHeight();
                //设置图片放大但比例
                double scale = 1.25;
                //计算这次要放大的比例
                scaleWidth = (float) (scaleWidth * scale);
                scaleHeight = (float) (scaleHeight * scale);
                //产生新的大小但Bitmap对象
                Matrix matrix = new Matrix();
                matrix.postScale(scaleWidth, scaleHeight);
                Bitmap resizeBmp = Bitmap.createBitmap(bitmap, 0, 0, bmpWidth, bmpHeight, matrix, true);
                img.setImageBitmap(resizeBmp);

            }
        });
        //图片减小
        zoomcontrols.setOnZoomOutClickListener(new OnClickListener() {

            public void onClick(View v) {
                int bmpWidth = bitmap.getWidth();
                int bmpHeight = bitmap.getHeight();
                //设置图片放大但比例
                double scale = 0.8;
                //计算这次要放大的比例
                scaleWidth = (float) (scaleWidth * scale);
                scaleHeight = (float) (scaleHeight * scale);
                //产生新的大小但Bitmap对象
                Matrix matrix = new Matrix();
                matrix.postScale(scaleWidth, scaleHeight);
                Bitmap resizeBmp = Bitmap.createBitmap(bitmap, 0, 0, bmpWidth, bmpHeight, matrix, true);
                img.setImageBitmap(resizeBmp);
            }

        });
    }
}

参考：http://blog.csdn.net/jianghuiquan/article/details/8350538