If you want to create Zoom-In and Zoom-out of an image using Touch events function check my below example. In below example First I have created a main layout named xml.layout then in xml.layout I have added 2 attributes, first is FrameLayout attribute and 2nd is ImageView attribute. In MainActivity I have used TouchListner, MotionEvent, Matrix method.
See the below example code it will clearly described you how to create Zoom-In & Zoom-Out function.

Step(1)MainActivity-

public class MainActivity extends Activity implements View.OnTouchListener {

        private static final String TAG = "Touch";
        @SuppressWarnings("unused")
        private static final float MIN_ZOOM = 1f, MAX_ZOOM = 1f;

        Matrix matrix = new Matrix();
        Matrix savedMatrix = new Matrix();

        // The 3 states (events) which the user is trying to perform
        static final int NONE = 0;
        static final int DRAG = 1;
        static final int ZOOM = 2;
        int mode = NONE;

        // these PointF objects are used to record the point(s) the user is touching
        PointF start = new PointF();
        PointF mid = new PointF();
        float oldDist = 1f;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            // TODO Auto-generated method stub
            super.onCreate(savedInstanceState);
            setContentView(R.layout.Train_map);
            ImageView view = (ImageView) findViewById(R.id.imageView1);
            view.setOnTouchListener(this);
        }

        @Override
        public boolean onTouch(View v, MotionEvent event) {
            ImageView view = (ImageView) v;
            view.setScaleType(ImageView.ScaleType.MATRIX);
            float scale;

            dumpEvent(event);
            // Handle touch events here...

            switch (event.getAction() & MotionEvent.ACTION_MASK) {
                case MotionEvent.ACTION_DOWN: // first finger down only
                    savedMatrix.set(matrix);
                    start.set(event.getX(), event.getY());
                    Log.d(TAG, "mode=DRAG"); // write to LogCat
                    mode = DRAG;
                    break;

                case MotionEvent.ACTION_UP:
                case MotionEvent.ACTION_POINTER_UP:

                    mode = NONE;
                    Log.d(TAG, "mode=NONE");
                    break;

                case MotionEvent.ACTION_POINTER_DOWN:
                    oldDist = spacing(event);
                    Log.d(TAG, "oldDist=" + oldDist);
                    if (oldDist > 5f) {
                        savedMatrix.set(matrix);
                        midPoint(mid, event);
                        mode = ZOOM;
                        Log.d(TAG, "mode=ZOOM");
                    }
                    break;

                case MotionEvent.ACTION_MOVE:

                    if (mode == DRAG) {
                        matrix.set(savedMatrix);
                        matrix.postTranslate(event.getX() - start.x, event.getY()
                                - start.y); /*
                                     * create the transformation in the matrix
                                     * of points
                                     */
                    } else if (mode == ZOOM) {
                        // pinch zooming
                        float newDist = spacing(event);
                        Log.d(TAG, "newDist=" + newDist);
                        if (newDist > 5f) {
                            matrix.set(savedMatrix);
                            scale = newDist / oldDist;
                    /*
                     * setting the scaling of the matrix...if scale > 1 means
                     * zoom in...if scale < 1 means zoom out
                     */
                            matrix.postScale(scale, scale, mid.x, mid.y);
                        }
                    }
                    break;
            }

            view.setImageMatrix(matrix); // display the transformation on screen

            return true;
        }
        private float spacing(MotionEvent event) {
            float x = event.getX(0) - event.getX(1);
            float y = event.getY(0) - event.getY(1);
            return FloatMath.sqrt(x * x + y * y);
        }


        private void midPoint(PointF point, MotionEvent event) {
            float x = event.getX(0) + event.getX(1);
            float y = event.getY(0) + event.getY(1);
            point.set(x / 2, y / 2);
        }

        private void dumpEvent(MotionEvent event) {
            String names[] = { "DOWN", "UP", "MOVE", "CANCEL", "OUTSIDE",
                    "POINTER_DOWN", "POINTER_UP", "7?", "8?", "9?" };
            StringBuilder sb = new StringBuilder();
            int action = event.getAction();
            int actionCode = action & MotionEvent.ACTION_MASK;
            sb.append("event ACTION_").append(names[actionCode]);

            if (actionCode == MotionEvent.ACTION_POINTER_DOWN
                    || actionCode == MotionEvent.ACTION_POINTER_UP) {
                sb.append("(pid ").append(
                        action >> MotionEvent.ACTION_POINTER_ID_SHIFT);
                sb.append(")");
            }

            sb.append("[");
            for (int i = 0; i < event.getPointerCount(); i++) {
                sb.append("#").append(i);
                sb.append("(pid ").append(event.getPointerId(i));
                sb.append(")=").append((int) event.getX(i));
                sb.append(",").append((int) event.getY(i));
                if (i + 1 < event.getPointerCount())
                    sb.append(";");
            }

            sb.append("]");
            Log.d("Touch Event", sb.toString());
        }
    }




Step(2)-main.xml layout-


   <?xml version="1.0" encoding="utf-8"?>
 <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:src="@drawable/img" />

</FrameLayout>