zoom an image view on click - android

I just want your help on a simple matter,

I have an activity (android application) that includes three tabs showing information. In one of those tabs, i have an image view. The picture is loaded through an async task because i have to retrieve the picture from the database.

Anyway i want to zoom in on the image when i click on it. Anyone got a good tutorial for it? Because i have to write the code inside the async task of the fragment tab.

class AsyncCallWS3 extends AsyncTask<String, Void, String> {

        ImageView img;
        Context context; 
        boolean check;
        Bitmap bm = null;
        
        public AsyncCallWS3(ImageView  img,Context context) {
                // TODO Auto-generated constructor stub
                this.img = img;
                this.context = context;
        }

        @Override
        protected String doInBackground(String... params) {
                String result;
                result = SponsorWebService.getSponsor("getDetails", "abed", "kader");
                this.Execute();
                return result;
        }
        
        protected void Execute(){
                String result;
                byte[] byteArray;
                result = ImageService.getImage("ralph", "kesrouani","getImage");
                
                byteArray = Base64.decode(result);
                
                bm = BitmapFactory.decodeByteArray(byteArray,0,byteArray.length);
                
                Bitmap resized = Bitmap.createScaledBitmap(bm, 60, 70, true);
                img.setImageBitmap(resized);
                
                img.setOnClickListener(new OnClickListener() {
                        
                        
                        }
                });
        }
    }