WPF

//
// Summary:
//     Initializes a new instance of the System.Windows.Input.RoutedUICommand class,
//     using the specified descriptive text, declared name, owner type, and input gestures.
//
//
// Parameters:
//   text:
//     Descriptive text for the command.
//
//   name:
//     The declared name of the command for serialization.
//
//   ownerType:
//     The type that is registering the command.
//
//   inputGestures:
//     A collection of gestures to associate with the command.
//
// Exceptions:
//   T:System.ArgumentNullException:
//     name is null.
//
//   T:System.ArgumentException:
//     ownerType is null.
public RoutedUICommand(string text, string name, Type ownerType, InputGestureCollection inputGestures)
    : base(name, ownerType, inputGestures)
{
    if (text == null)
    {
        throw new ArgumentNullException("text");
    }

    _text = text;
}



    //
    // Summary:
    //     Initializes a new instance of the System.Windows.Input.KeyGesture class with
    //     the specified System.Windows.Input.Key and System.Windows.Input.ModifierKeys.
    //
    //
    // Parameters:
    //   key:
    //     The key associated with the gesture.
    //
    //   modifiers:
    //     The modifier keys associated with the gesture.
    //
    // Exceptions:
    //   T:System.ComponentModel.InvalidEnumArgumentException:
    //     modifiers is not a valid System.Windows.Input.ModifierKeys -or- key is not a
    //     valid System.Windows.Input.Key.
    //
    //   T:System.NotSupportedException:
    //     key and modifiers do not form a valid System.Windows.Input.KeyGesture.
    public KeyGesture(Key key, ModifierKeys modifiers)
        : this(key, modifiers, string.Empty, validateGesture: true)
    {
    }

//xaml

<Window x:Class="WpfApp107.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:WpfApp107"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Window.CommandBindings>
        <CommandBinding Command="Open" Executed="OnOpen"/>
        <CommandBinding Command="IncreaseZoom" Executed="OnZoomIn" CanExecute="OnIsImageExist"/>
        <CommandBinding Command="DecreaseZoom" Executed="OnZoomOut" CanExecute="OnIsImageExist"/>
        <CommandBinding Command="local:Commands.ZoomNormalCommand" Executed="OnZoomNormal" CanExecute="OnIsImageExist"/>
    </Window.CommandBindings>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition />
        </Grid.RowDefinitions>
        <ToolBar FontSize="20">
            <Button Content="Open..." Command="Open" Margin="6"/>
            <Button Content="Zoom In" Command="IncreaseZoom" Margin="6"/>
            <Button Content="Zoom Out" Command="DecreaseZoom" Margin="6"/>
            <Button Command="local:Commands.ZoomNormalCommand" Content="Normal" Margin="6"/>
        </ToolBar>
        <ScrollViewer Grid.Row="1" HorizontalScrollBarVisibility="Auto"
                      VerticalScrollBarVisibility="Auto">
            <Image Source="{Binding ImagePath}">
                <Image.LayoutTransform>
                    <ScaleTransform ScaleX="{Binding ZoomLevel}"
                                    ScaleY="{Binding ZoomLevel}"/>
                </Image.LayoutTransform> 
            </Image>
        </ScrollViewer>
    </Grid>
</Window>


//xaml.cs
using Microsoft.Win32;
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;

namespace WpfApp107
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        ImageData _image;
        public MainWindow()
        {
            InitializeComponent();
        }

        private void OnOpen(object sender, ExecutedRoutedEventArgs e)
        {
            var dlg = new OpenFileDialog
            {
                Filter = "Image Files|*.jpg;*.png;*.bmp;*.gif"
            };
            if (dlg.ShowDialog() == true)
            {
                _image=new ImageData(dlg.FileName);
                DataContext = _image;
            }
        }         

        private void OnZoomIn(object sender, ExecutedRoutedEventArgs e)
        {
            _image.ZoomLevel *= 1.2;
        }

        private void OnZoomOut(object sender, ExecutedRoutedEventArgs e)
        {
            _image.ZoomLevel /= 1.2;
        }

        private void OnIsImageExist(object sender, CanExecuteRoutedEventArgs e)
        {
            e.CanExecute = _image != null;
        }

        private void OnZoomNormal(object sender, ExecutedRoutedEventArgs e)
        {
            _image.ZoomLevel = 1.0;
        }
    }

    class ImageData : INotifyPropertyChanged
    {
        public string ImagePath { get; private set; }

        public ImageData(string pathValue)
        {
            ImagePath=pathValue;
        }

        double zoomLevel = 1.0;
        public double ZoomLevel
        {
            get
            {
                return zoomLevel;
            }
            set
            {
                zoomLevel = value;
                OnPropertyChanged(nameof(ZoomLevel));   
            }

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

    static class Commands
    {
        static readonly RoutedUICommand _zoomNormalCommand =
            new RoutedUICommand("Zoom Normal", "Normal", typeof(Commands),
                new InputGestureCollection(new[] {new KeyGesture(Key.N,ModifierKeys.Alt)}));
        public static RoutedUICommand ZoomNormalCommand
        {
            get
            {
                return _zoomNormalCommand;
            }
        }
    }
}