批量修改图片的尺寸(c#)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using System.Drawing;
using System.Drawing.Imaging;
namespace ChangeImgSize
{
    class Program
    {
        static void Main(string[] args)
        {
            int num = 0;
            if (!System.IO.Directory.Exists("Img"))
            {
                System.IO.Directory.CreateDirectory("Img");
                Console.WriteLine("已创建Img目录，请把需要处理的图片放到该目录下");
                Console.ReadKey(true);
                return;
            }
            if (!System.IO.Directory.Exists("NewImg"))
            {
                System.IO.Directory.CreateDirectory("NewImg");
            }
            Console.WriteLine("请输入需要缩小的倍数");
            double size = Convert.ToDouble(Console.ReadLine());
            string[] fileStrs = System.IO.Directory.GetFiles("Img");
            foreach (string s in fileStrs)
            {
                System.IO.FileInfo info = new System.IO.FileInfo(s);
                if (info.Extension == ".png" || info.Extension == ".jpg")
                {
                    Image img = GetFile(s);
                    Bitmap bit = GetNewSizeBitmap(img,size);
                    SaveImage(bit, info.Name, info.Extension);
                }
                ++num;
            }
            Console.WriteLine("共处理：" + num + "张图片，已经保存到NewImg目录中。");
            Console.ReadKey(true);
        }
        static public Image GetFile(string path)
        {
            FileStream stream = File.OpenRead(path);
            int fileLength = 0;
            fileLength = (int)stream.Length;
            Byte[] image = new Byte[fileLength];
            stream.Read(image, 0, fileLength);
            System.Drawing.Image result = System.Drawing.Image.FromStream(stream);
            stream.Close();
            return result;
        }
        static public Bitmap GetNewSizeBitmap(Image img , double size){
            int newWidth = Convert.ToInt32(img.Width / size);
            int newHeight = Convert.ToInt32(img.Height / size);
            Size s = new Size(newWidth, newHeight);
            Bitmap newBit = new Bitmap(img, s);
            return newBit;
        }
        static public void SaveImage(Bitmap bit,string name,string ext)
        {
            bit.Save(@"NewImg\" + name);
            bit.Dispose();
            Console.WriteLine("已处理:" + name);
        }
    }
}