C# convert ImageSource to byte array

using Microsoft.Win32;
using System;
using System.Globalization;
using System.IO;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;


public byte[] ImageSourceToBytes(ImageSource imageSource)
{
    byte[] bytes = null;
    var bitmapSource = imageSource as BitmapSource;
    if (bitmapSource != null)
    {
        JpegBitmapEncoder encoder = new JpegBitmapEncoder();
        encoder.Frames.Add(BitmapFrame.Create(bitmapSource));
        using (var stream = new MemoryStream())
        {
            encoder.Save(stream);
            bytes = stream.ToArray();
        }
    }
    return bytes;
}