WPF Image automatically display image via System.Timers.Timer ,pause and resume, scaletransform

<Window x:Class="WpfApp408.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp408"
        mc:Ignorable="d"
        WindowState="Maximized"
        WindowStyle="None"
        AllowsTransparency="True"
        KeyDown="Window_KeyDown"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Image x:Name="img" Source="{Binding ImgUrl,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
               RenderOptions.BitmapScalingMode="Fant"
               MouseWheel="Image_MouseWheel">
            <Image.RenderTransform>
                <TransformGroup>
                    <ScaleTransform x:Name="scaler"/>
                </TransformGroup>
            </Image.RenderTransform>
        </Image>
        <TextBlock Text="{Binding SeqId,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
                   HorizontalAlignment="Right"
                   VerticalAlignment="Bottom"
                   Width="200"
                   Foreground="Red"
                   FontSize="50"
                   Panel.ZIndex="2"/>
    </Grid>
</Window>


//cs
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.IO;
using System.Runtime.InteropServices;
using System.Data.SqlTypes;

namespace WpfApp408
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window, INotifyPropertyChanged
    {
        private List<string> imgsList { get; set; }
        private int idx = 0;
        public int Idx
        {
            get
            {
                return idx;
            }
            set
            {
                if(value!=idx)
                {
                    idx = value;
                    OnPropertyChanged(nameof(Idx));
                }
            }
        }

        private int seqId = 0;
        public int SeqId
        {
            get
            {
                return seqId;
            }
            set
            {
                if (value!=seqId)
                {
                    seqId = value;
                    OnPropertyChanged(nameof(SeqId));
                }
            }
        }

        private int imgsCount = 0;
        private bool isPaused = false;

        public MainWindow()
        {
            InitializeComponent();
            this.DataContext = this;
            imgsList = new List<string>(Directory.GetFiles(@"../../Images"));
            imgsCount = imgsList.Count;
            System.Timers.Timer tmr = new System.Timers.Timer();
            tmr.Elapsed += Tmr_Elapsed;
            tmr.Interval = 100;
            tmr.Start();
        }

        private void Tmr_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
        {
            if(isPaused)
            {
                return;
            }
            if (++Idx >= imgsCount)
            {
                Idx = 0;
            }
            ImgUrl = imgsList[Idx];
            ++SeqId;
            Dispatcher.BeginInvoke(new Action(() =>
            {
                scaler.ScaleX = 1.0;
                scaler.ScaleY = 1.0;
                scaler.CenterX = 0;
                scaler.CenterY = 0;
            }));
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void OnPropertyChanged(string propertyName)
        {
            var handler = PropertyChanged;
            if (handler != null)
            {
                handler?.Invoke(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        private string imgUrl;
        public string ImgUrl
        {
            get
            {
                return imgUrl;
            }
            set
            {
                if (value != imgUrl)
                {
                    imgUrl = value;
                    OnPropertyChanged(nameof(ImgUrl));
                }
            }
        }

        private void Window_KeyDown(object sender, KeyEventArgs e)
        {
            if (Keyboard.Modifiers == ModifierKeys.Control && e.Key == Key.C)
            {
                var msgResult = MessageBox.Show("Are you sure to close this window?", "Close this Window",
                    MessageBoxButton.YesNo, MessageBoxImage.Question, MessageBoxResult.Yes);
                if (msgResult == MessageBoxResult.Yes)
                {
                    this.Close();
                }
            }
            else if(e.Key==Key.Space)
            {
                isPaused=!isPaused;
            }
        }

        private void Image_MouseWheel(object sender, MouseWheelEventArgs e)
        {
            if(e.Delta>0)
            {
                scaler.ScaleX *= 1.2;
                scaler.ScaleY *= 1.2;
            }
            else
            {
                scaler.ScaleX /= 1.2;
                scaler.ScaleY /= 1.2;
            }
            scaler.CenterX = e.GetPosition(img).X;
            scaler.CenterY = e.GetPosition(img).Y;
        }
    }
}