c# 中base64字符串和图片的相互转换

c#base64字符串转图片用到了bitmap类，封装 GDI+ 位图，此位图由图形图像及其特性的像素数据组成。 Bitmap 是用于处理由像素数据定义的图像的对象。

具体bitmap类是什么可以自己百度查询，这里就不多介绍了。

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#region base64转图片         /// <summary>         /// 图片上传 Base64解码         /// </summary>         /// <param name="dataURL">Base64数据</param>         /// <param name="imgName">图片名字</param>         /// <returns>返回一个相对路径</returns>         public string decodeBase64ToImage(string dataURL,string imgName)         {               string filename = "";//声明一个string类型的相对路径               String base64 = dataURL.Substring(dataURL.IndexOf(",") + 1);      //将‘，’以前的多余字符串删除             System.Drawing.Bitmap bitmap = null;//定义一个Bitmap对象，接收转换完成的图片               try//会有异常抛出，try，catch一下             {                   byte[] arr = Convert.FromBase64String(base64);//将纯净资源Base64转换成等效的8位无符号整形数组                   System.IO.MemoryStream ms = new System.IO.MemoryStream(arr);//转换成无法调整大小的MemoryStream对象                 bitmap = new System.Drawing.Bitmap(ms);//将MemoryStream对象转换成Bitmap对象                   filename ="Knowledge_" + imgName + ".jpg";//所要保存的相对路径及名字                 string url =HttpRuntime.AppDomainAppPath.ToString();                 string tmpRootDir = System.Web.HttpContext.Current.Server.MapPath(System.Web.HttpContext.Current.Request.ApplicationPath.ToString()); //获取程序根目录                  string imagesurl2 = tmpRootDir + filename; //转换成绝对路径                  bitmap.Save(imagesurl2, System.Drawing.Imaging.ImageFormat.Jpeg);//保存到服务器路径                 //bitmap.Save(filePath + ".bmp", System.Drawing.Imaging.ImageFormat.Bmp);                 //bitmap.Save(filePath + ".gif", System.Drawing.Imaging.ImageFormat.Gif);                 //bitmap.Save(filePath + ".png", System.Drawing.Imaging.ImageFormat.Png);                 ms.Close();//关闭当前流，并释放所有与之关联的资源                 bitmap.Dispose();             }             catch (Exception e)             {                string massage= e.Message;             }             return filename;//返回相对路径         }         #endregion           #region 图片转base64         /// <summary>         /// 图片转base64         /// </summary>         /// <param name="path">图片路径</param><br>        /// <returns>返回一个base64字符串</returns>         public string decodeImageToBase64(string path) {             path = "E:/vs 2015/newaqtcprj/WEB/UpFile/2018/12/20181229174708_7471722c425a2ec08fa513ddf4f8c76306d55fbb0fbd9d8.jpg";             string base64str = "";               //站点文件目录             string fileDir = HttpContext.Current.Server.MapPath("/");             string[] arrfileDir = fileDir.Split('\\');             fileDir = arrfileDir[0] + "\\" + arrfileDir[1] + "\\" + arrfileDir[2];             try             {                 //读图片转为Base64String                 System.Drawing.Bitmap bmp = new System.Drawing.Bitmap(Path.Combine(fileDir, "WEB\\UpFile\\2018\\12\\20181229174708_7471722c425a2ec08fa513ddf4f8c76306d55fbb0fbd9d8.jpg"));                 //System.Drawing.Bitmap bmp = new System.Drawing.Bitmap(path);                 MemoryStream ms = new MemoryStream();                 bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);                 byte[] arr = new byte[ms.Length];                 ms.Position = 0;                 ms.Read(arr, 0, (int)ms.Length);                 ms.Close();                 bmp.Dispose();                 base64str = Convert.ToBase64String(arr);             }             catch (Exception e)             {                 string mss = e.Message;             }             return "data:image/jpg;base64," + base64str;         }         #endregion