c# 图片 与 BASE64 字符串 互相转换。

 using System;
 using System.Collections.Generic;
 using System.Drawing;
 using System.IO;
 using System.Linq;
 using System.Web;
 using System.Drawing.Imaging;
 // 博客园  aC#Coder 整理
 namespace Html5Image.Tools
 {
     public class ImageTool
     {
         //图片 转为    base64编码的文本
         public static string ImgToBase64String(Bitmap bmp)
         {
             //Bitmap bmp = new Bitmap(Imagefilename);
             //this.pictureBox1.Image = bmp;
             //FileStream fs = new FileStream(Imagefilename + ".txt", FileMode.Create);
             //StreamWriter sw = new StreamWriter(fs);

             MemoryStream ms = new MemoryStream();
             bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
             byte[] arr = new byte[ms.Length];
             ms.Position = ;
             ms.Read(arr, , (int)ms.Length);
             ms.Close();
             String strbaser64 = Convert.ToBase64String(arr);

             return strbaser64;
         }

         public static Bitmap Base64StringToImage(string base64Img)
         {
             byte[] bytes = Convert.FromBase64String(base64Img);
             MemoryStream ms = new MemoryStream();
             ms.Write(bytes, , bytes.Length);
             Bitmap bmp = new Bitmap(ms);

             return bmp;
         }

         /// <summary>
         /// 保存图片
         /// </summary>
         /// <param name="base64Img"></param>
         /// <param name="imgPath"></param>
         /// <param name="imgFormat">EX: System.Drawing.Imaging.Jpeg </param>
         public static void SaveFile(string base64Img, string imgPath, ImageFormat imgFormat )
         {
             string dir = Path.GetDirectoryName(imgPath);
             if (!Directory.Exists(dir))
             {
                 Directory.CreateDirectory(dir);
             }
             var bitmap = Base64StringToImage(base64Img);
             bitmap.Save(imgPath, imgFormat);
         }
     }
 }