static public WriteableBitmap wb;
        DispatcherTimer _timer = new DispatcherTimer();


            var task = Task.Run(() => {
                int width;
                int height;
                int stride;

                byte[] imgdata1;

                width = 250;
                height = 250;
                stride = width * 4;
                imgdata1 = new byte[height * stride];

                for (int row = 0; row < height; row++)
                {
                    // System.Threading.Thread.Sleep(20);
                    for (int col = 0; col < width; col++)
                    {
                        SetPixelPbgra32(ref imgdata1, row, col, stride, Color.FromArgb(Convert.ToByte((2 * row * col) % 256), Convert.ToByte((2 * row * col) % 256), Convert.ToByte((row * col) % 256), Convert.ToByte((row * col) % 256)));  //Colors.Blue)
                    }
                    BitmapSource gradient1;
                    gradient1 = BitmapSource.Create(width, height, 96, 96, PixelFormats.Pbgra32, null, imgdata1, stride);


                    wb = new WriteableBitmap(gradient1);
                    wb.Freeze();
                }
            } 

     _timer.Tick += _timer_Tick;
     _timer.Interval = new TimeSpan(0, 0, 0, 0, 1000); 
     _timer.Start();

      void _timer_Tick(object sender, EventArgs e)
      {
         Dispatcher.BeginInvoke(new Action(() =>
            {
                myImage.Source = wb;
            }));
      }