private async void LoadImage(object sender, RoutedEventArgs e)
        {
            var picker = new FileOpenPicker();
 
            picker.FileTypeFilter.Add(".png");
            picker.FileTypeFilter.Add(".jpg");
            picker.FileTypeFilter.Add(".gif");
            picker.FileTypeFilter.Add(".jpeg");
 
            StorageFile file = await picker.PickSingleFileAsync();
           
            if (file != null)
            {
                using (var fileStream = await file.OpenStreamForReadAsync())
                {
                    try
                    {
                        LoadImageStream(fileStream);
                    }
                    catch (Exception ex)
                    {
                        LoadDefaultImage();
                        MessageDialog md = new MessageDialog("Image format not supported, error: \n" + ex.Message, "");
                        md.ShowAsync();
                    }
                }
            }
        }