C# Base64转换

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using System.Drawing;
using System.Drawing.Imaging;

namespace ConsoleApplication10
{
    class Program
    {
        static void Main(string[] args)
        {
            string str = @"假设这里是一段base64编码的字符串";

            Regex rgx = new Regex(@" ");
            str = rgx.Replace(str, @"+");
            byte[] data = new byte[str.Length];
            data = Convert.FromBase64String(str);
            MemoryStream ms = new MemoryStream(data);
            Image img = Image.FromStream(ms);
            //image.Save(@"C:\Users\Administrator\Desktop\a1a1.png", ImageFormat.Png);
            Bitmap image = new Bitmap(img);
            Bitmap image1 = new Bitmap(120, 120);
            int width = image.Width;
            int height = image.Height;
            Graphics g = Graphics.FromImage(image1);
            Rectangle rect = new Rectangle(50, 25, 120, 120);
            g.DrawImage(image, 0, 0, rect, GraphicsUnit.Pixel);
            //string url = Server.MapPath(@"~/saveimg/as.png");
            image1.Save(@"C:\Users\Administrator\Desktop\a2.png", ImageFormat.Png);
        }
    }
}