C# 生成缩略图

好久没写博客了，一个字：忙

今天索性随便贴一些代码，这些代码主要是为了解决图片的压缩问题

我们都知道，移动端的图片不易过大，否则就会拉低加载速度！影响用户体验

因此，我们就有必要通过程序生成大图片的缩略图！这种场景常用在加载图片列表时

比如，有十张大小2M左右的图片需要加载出来，那么在完成加载完成就需要20M的网络资源，因此，使用缩略图是有必要的

好了，废话基本说完了，下面看代码：

    public class PicManger
    {
        private Image srcImage;
        private string srcFileName;

        /// <summary>
        /// 创建
        /// </summary>
        /// <param name="FileName">原始图片路径</param>
        public bool SetImage(string FileName)
        {
            srcFileName = Utils.GetMapPath(FileName);
            try
            {
                srcImage = Image.FromFile(srcFileName);
            }
            catch
            {
                return false;
            }
            return true;

        }

        /// <summary>
        /// 回调
        /// </summary>
        /// <returns></returns>
        public bool ThumbnailCallback()
        {
            return false;
        }

        /// <summary>
        /// 生成缩略图,返回缩略图的Image对象
        /// </summary>
        /// <param name="Width">缩略图宽度</param>
        /// <param name="Height">缩略图高度</param>
        /// <returns>缩略图的Image对象</returns>
        public Image GetImage(int Width, int Height)
        {
            Image img;
            Image.GetThumbnailImageAbort callb = new Image.GetThumbnailImageAbort(ThumbnailCallback);
            img = srcImage.GetThumbnailImage(Width, Height, callb, IntPtr.Zero);
            return img;
        }

        /// <summary>
        /// 保存缩略图
        /// </summary>
        /// <param name="Width"></param>
        /// <param name="Height"></param>
        public void SaveThumbnailImage(int Width, int Height)
        {
            switch (Path.GetExtension(srcFileName).ToLower())
            {
                case ".png":
                    SaveImage(Width, Height, ImageFormat.Png);
                    break;
                case ".gif":
                    SaveImage(Width, Height, ImageFormat.Gif);
                    break;
                default:
                    SaveImage(Width, Height, ImageFormat.Jpeg);
                    break;
            }
        }

        /// <summary>
        /// 生成缩略图并保存
        /// </summary>
        /// <param name="Width">缩略图的宽度</param>
        /// <param name="Height">缩略图的高度</param>
        /// <param name="imgformat">保存的图像格式</param>
        /// <returns>缩略图的Image对象</returns>
        public void SaveImage(int Width, int Height, ImageFormat imgformat)
        {
            if (imgformat != ImageFormat.Gif && (srcImage.Width > Width) || (srcImage.Height > Height))
            {
                Image img;
                Image.GetThumbnailImageAbort callb = new Image.GetThumbnailImageAbort(ThumbnailCallback);
                img = srcImage.GetThumbnailImage(Width, Height, callb, IntPtr.Zero);
                srcImage.Dispose();
                img.Save(srcFileName, imgformat);
                img.Dispose();
            }
        }

        #region Helper

        /// <summary>
        /// 保存图片
        /// </summary>
        /// <param name="image">Image 对象</param>
        /// <param name="savePath">保存路径</param>
        /// <param name="ici">指定格式的编解码参数</param>
        private static void SaveImage(Image image, string savePath, ImageCodecInfo ici)
        {
            //设置 原图片 对象的 EncoderParameters 对象
            EncoderParameters parameters = new EncoderParameters(1);
            parameters.Param[0] = new EncoderParameter(Encoder.Quality, ((long)100));
            image.Save(savePath, ici, parameters);
            parameters.Dispose();
        }

        /// <summary>
        /// 获取图像编码解码器的所有相关信息
        /// </summary>
        /// <param name="mimeType">包含编码解码器的多用途网际邮件扩充协议 (MIME) 类型的字符串</param>
        /// <returns>返回图像编码解码器的所有相关信息</returns>
        private static ImageCodecInfo GetCodecInfo(string mimeType)
        {
            ImageCodecInfo[] CodecInfo = ImageCodecInfo.GetImageEncoders();
            foreach (ImageCodecInfo ici in CodecInfo)
            {
                if (ici.MimeType == mimeType)
                    return ici;
            }
            return null;
        }

        /// <summary>
        /// 计算新尺寸
        /// </summary>
        /// <param name="width">原始宽度</param>
        /// <param name="height">原始高度</param>
        /// <param name="maxWidth">最大新宽度</param>
        /// <param name="maxHeight">最大新高度</param>
        /// <returns></returns>
        private static Size ResizeImage(int width, int height, int maxWidth, int maxHeight)
        {
            //此次2012-02-05修改过=================
            if (maxWidth <= 0)
                maxWidth = width;
            if (maxHeight <= 0)
                maxHeight = height;
            //以上2012-02-05修改过=================
            decimal MAX_WIDTH = (decimal)maxWidth;
            decimal MAX_HEIGHT = (decimal)maxHeight;
            decimal ASPECT_RATIO = MAX_WIDTH / MAX_HEIGHT;

            int newWidth, newHeight;
            decimal originalWidth = (decimal)width;
            decimal originalHeight = (decimal)height;

            if (originalWidth > MAX_WIDTH || originalHeight > MAX_HEIGHT)
            {
                decimal factor;
                // determine the largest factor 
                if (originalWidth / originalHeight > ASPECT_RATIO)
                {
                    factor = originalWidth / MAX_WIDTH;
                    newWidth = Convert.ToInt32(originalWidth / factor);
                    newHeight = Convert.ToInt32(originalHeight / factor);
                }
                else
                {
                    factor = originalHeight / MAX_HEIGHT;
                    newWidth = Convert.ToInt32(originalWidth / factor);
                    newHeight = Convert.ToInt32(originalHeight / factor);
                }
            }
            else
            {
                newWidth = width;
                newHeight = height;
            }
            return new Size(newWidth, newHeight);
        }

        /// <summary>
        /// 得到图片格式
        /// </summary>
        /// <param name="name">文件名称</param>
        /// <returns></returns>
        public static ImageFormat GetFormat(string name)
        {
            string ext = name.Substring(name.LastIndexOf(".") + 1);
            switch (ext.ToLower())
            {
                case "jpg":
                case "jpeg":
                    return ImageFormat.Jpeg;
                case "bmp":
                    return ImageFormat.Bmp;
                case "png":
                    return ImageFormat.Png;
                case "gif":
                    return ImageFormat.Gif;
                default:
                    return ImageFormat.Jpeg;
            }
        }
        #endregion

        /// <summary>
        /// 制作小正方形
        /// </summary>
        /// <param name="image">图片对象</param>
        /// <param name="newFileName">新地址</param>
        /// <param name="newSize">长度或宽度</param>
        public static void MakeSquareImage(Image image, string newFileName, int newSize)
        {
            int i = 0;
            int width = image.Width;
            int height = image.Height;
            if (width > height)
                i = height;
            else
                i = width;

            Bitmap b = new Bitmap(newSize, newSize);

            try
            {
                Graphics g = Graphics.FromImage(b);
                //设置高质量插值法
                g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                //设置高质量,低速度呈现平滑程度
                g.SmoothingMode = SmoothingMode.AntiAlias;
                g.PixelOffsetMode = PixelOffsetMode.HighQuality;
                //清除整个绘图面并以透明背景色填充
                g.Clear(Color.Transparent);
                if (width < height)
                    g.DrawImage(image, new Rectangle(0, 0, newSize, newSize), new Rectangle(0, (height - width) / 2, width, width), GraphicsUnit.Pixel);
                else
                    g.DrawImage(image, new Rectangle(0, 0, newSize, newSize), new Rectangle((width - height) / 2, 0, height, height), GraphicsUnit.Pixel);

                SaveImage(b, newFileName, GetCodecInfo("image/" + GetFormat(newFileName).ToString().ToLower()));
            }
            finally
            {
                image.Dispose();
                b.Dispose();
            }
        }

        /// <summary>
        /// 制作小正方形
        /// </summary>
        /// <param name="fileName">图片文件名</param>
        /// <param name="newFileName">新地址</param>
        /// <param name="newSize">长度或宽度</param>
        public static void MakeSquareImage(string fileName, string newFileName, int newSize)
        {
            MakeSquareImage(Image.FromFile(fileName), newFileName, newSize);
        }

        /// <summary>
        /// 制作远程小正方形
        /// </summary>
        /// <param name="url">图片url</param>
        /// <param name="newFileName">新地址</param>
        /// <param name="newSize">长度或宽度</param>
        public static void MakeRemoteSquareImage(string url, string newFileName, int newSize)
        {
            Stream stream = GetRemoteImage(url);
            if (stream == null)
                return;
            Image original = Image.FromStream(stream);
            stream.Close();
            MakeSquareImage(original, newFileName, newSize);
        }

        /// <summary>
        /// 制作缩略图
        /// </summary>
        /// <param name="original">图片对象</param>
        /// <param name="newFileName">新图路径</param>
        /// <param name="maxWidth">最大宽度</param>
        /// <param name="maxHeight">最大高度</param>
        public static void MakeThumbnailImage(Image original, string newFileName, int maxWidth, int maxHeight)
        {
            Size _newSize = ResizeImage(original.Width, original.Height, maxWidth, maxHeight);

            using (Image displayImage = new Bitmap(original, _newSize))
            {
                try
                {
                    displayImage.Save(newFileName, original.RawFormat);
                }
                finally
                {
                    original.Dispose();
                }
            }
        }

        /// <summary>
        /// 制作缩略图
        /// </summary>
        /// <param name="fileName">文件名</param>
        /// <param name="newFileName">新图路径</param>
        /// <param name="maxWidth">最大宽度</param>
        /// <param name="maxHeight">最大高度</param>
        public static void MakeThumbnailImage(string fileName, string newFileName, int maxWidth, int maxHeight)
        {
            //2012-02-05修改过，支持替换
            byte[] imageBytes = File.ReadAllBytes(fileName);
            Image img = Image.FromStream(new System.IO.MemoryStream(imageBytes));
            MakeThumbnailImage(img, newFileName, maxWidth, maxHeight);
            //原文
            //MakeThumbnailImage(Image.FromFile(fileName), newFileName, maxWidth, maxHeight);
        }

        #region 2012-2-19 新增生成图片缩略图方法
        /// <summary>
        /// 生成缩略图
        /// </summary>
        /// <param name="fileName">源图路径（绝对路径）</param>
        /// <param name="newFileName">缩略图路径（绝对路径）</param>
        /// <param name="width">缩略图宽度</param>
        /// <param name="height">缩略图高度</param>
        /// <param name="mode">生成缩略图的方式</param>    
        public static void MakeThumbnailImage(string fileName, string newFileName, int width, int height, string mode)
        {
            Image originalImage = Image.FromFile(fileName);
            int towidth = width;
            int toheight = height;

            int x = 0;
            int y = 0;
            int ow = originalImage.Width;
            int oh = originalImage.Height;

            switch (mode)
            {
                case "HW"://指定高宽缩放（可能变形）                
                    break;
                case "W"://指定宽，高按比例                    
                    toheight = originalImage.Height * width / originalImage.Width;
                    break;
                case "H"://指定高，宽按比例
                    towidth = originalImage.Width * height / originalImage.Height;
                    break;
                case "Cut"://指定高宽裁减（不变形）                
                    if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
                    {
                        oh = originalImage.Height;
                        ow = originalImage.Height * towidth / toheight;
                        y = 0;
                        x = (originalImage.Width - ow) / 2;
                    }
                    else
                    {
                        ow = originalImage.Width;
                        oh = originalImage.Width * height / towidth;
                        x = 0;
                        y = (originalImage.Height - oh) / 2;
                    }
                    break;
                default:
                    break;
            }

            //新建一个bmp图片
            Bitmap b = new Bitmap(towidth, toheight);
            try
            {
                //新建一个画板
                Graphics g = Graphics.FromImage(b);
                //设置高质量插值法
                g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                //设置高质量,低速度呈现平滑程度
                g.SmoothingMode = SmoothingMode.AntiAlias;
                g.PixelOffsetMode = PixelOffsetMode.HighQuality;
                //清空画布并以透明背景色填充
                g.Clear(Color.Transparent);
                //在指定位置并且按指定大小绘制原图片的指定部分
                g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight), new Rectangle(x, y, ow, oh), GraphicsUnit.Pixel);

                SaveImage(b, newFileName, GetCodecInfo("image/" + GetFormat(newFileName).ToString().ToLower()));
            }
            catch (System.Exception e)
            {
                throw e;
            }
            finally
            {
                originalImage.Dispose();
                b.Dispose();
            }
        }
        #endregion

        #region 2012-10-30 新增图片裁剪方法
        /// <summary>
        /// 裁剪图片并保存
        /// </summary>
        /// <param name="fileName">源图路径（绝对路径）</param>
        /// <param name="newFileName">缩略图路径（绝对路径）</param>
        /// <param name="maxWidth">缩略图宽度</param>
        /// <param name="maxHeight">缩略图高度</param>
        /// <param name="cropWidth">裁剪宽度</param>
        /// <param name="cropHeight">裁剪高度</param>
        /// <param name="X">X轴</param>
        /// <param name="Y">Y轴</param>
        public static bool MakeThumbnailImage(string fileName, string newFileName, int maxWidth, int maxHeight, int cropWidth, int cropHeight, int X, int Y)
        {
            byte[] imageBytes = File.ReadAllBytes(fileName);
            Image originalImage = Image.FromStream(new System.IO.MemoryStream(imageBytes));
            Bitmap b = new Bitmap(cropWidth, cropHeight);
            try
            {
                using (Graphics g = Graphics.FromImage(b))
                {
                    //设置高质量插值法
                    g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                    //设置高质量,低速度呈现平滑程度
                    g.SmoothingMode = SmoothingMode.AntiAlias;
                    g.PixelOffsetMode = PixelOffsetMode.HighQuality;
                    //清空画布并以透明背景色填充
                    g.Clear(Color.Transparent);
                    //在指定位置并且按指定大小绘制原图片的指定部分
                    g.DrawImage(originalImage, new Rectangle(0, 0, cropWidth, cropHeight), X, Y, cropWidth, cropHeight, GraphicsUnit.Pixel);
                    Image displayImage = new Bitmap(b, maxWidth, maxHeight);
                    SaveImage(displayImage, newFileName, GetCodecInfo("image/" + GetFormat(newFileName).ToString().ToLower()));
                    return true;
                }
            }
            catch (System.Exception e)
            {
                throw e;
            }
            finally
            {
                originalImage.Dispose();
                b.Dispose();
            }
        }

        #endregion

        /// <summary>
        /// 制作远程缩略图
        /// </summary>
        /// <param name="url">图片URL</param>
        /// <param name="newFileName">新图路径</param>
        /// <param name="maxWidth">最大宽度</param>
        /// <param name="maxHeight">最大高度</param>
        public static void MakeRemoteThumbnailImage(string url, string newFileName, int maxWidth, int maxHeight)
        {
            Stream stream = GetRemoteImage(url);
            if (stream == null)
                return;
            Image original = Image.FromStream(stream);
            stream.Close();
            MakeThumbnailImage(original, newFileName, maxWidth, maxHeight);
        }

        /// <summary>
        /// 获取图片流
        /// </summary>
        /// <param name="url">图片URL</param>
        /// <returns></returns>
        private static Stream GetRemoteImage(string url)
        {
            HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
            request.Method = "GET";
            request.ContentLength = 0;
            request.Timeout = 20000;
            HttpWebResponse response = null;

            try
            {
                response = (HttpWebResponse)request.GetResponse();
                return response.GetResponseStream();
            }
            catch
            {
                return null;
            }
        }

        #region 动态剪切图片 2015年3-25日陈卧龙
        /// <summary>
        /// 动态裁剪图片并保存
        /// </summary>
        /// <param name="fileName">源图路径（绝对路径）</param>
        /// <param name="newFileName">缩略图路径（绝对路径）</param>
        /// <param name="num">将图片规则剪裁成的份数  规则图形  应该为偶数</param>
        ///算法代码参考：http://blog.163.com/smhily_min/blog/static/75206226201132815412644/
        ///  /// <param name="X">X轴</param>
        /// <param name="Y">Y轴</param>
        /// <param name="Xnum">水平切割的份数</param>
        /// <param name="Ynum">竖直切割的份数</param>
        /// <param name="i">for循环参数i</param>
        /// <returns></returns>
        public static bool cutImage(string fileName, string newFileName, int Xnum,int Ynum ,int i)
        {
            int maxWidth; int maxHeight; int cropWidth; int cropHeight; int X; int Y;
            //
            using (FileStream fs = new FileStream(fileName, FileMode.Open, FileAccess.Read))
            {
                System.Drawing.Image image = System.Drawing.Image.FromStream(fs);
                int width = image.Width;
                int height = image.Height;
                maxWidth = cropWidth = (int)Math.Round(Convert.ToDecimal(width / Xnum));
                maxHeight = cropHeight = (int)Math.Round(Convert.ToDecimal(height / Ynum));
                //
                X = (i % Xnum) * (width / Xnum);
                Y = (int)Math.Floor(Convert.ToDecimal(i / Xnum)) * (int)Math.Round(Convert.ToDecimal(height / Ynum));
            }
            //
            byte[] imageBytes = File.ReadAllBytes(fileName);
            Image originalImage = Image.FromStream(new System.IO.MemoryStream(imageBytes));
            Bitmap b = new Bitmap(cropWidth, cropHeight);
            try
            {
                using (Graphics g = Graphics.FromImage(b))
                {
                    //设置高质量插值法
                    g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                    //设置高质量,低速度呈现平滑程度
                    g.SmoothingMode = SmoothingMode.AntiAlias;
                    g.PixelOffsetMode = PixelOffsetMode.HighQuality;
                    //清空画布并以透明背景色填充
                    g.Clear(Color.Transparent);
                    //在指定位置并且按指定大小绘制原图片的指定部分
                    g.DrawImage(originalImage, new Rectangle(0, 0, cropWidth, cropHeight), X, Y, cropWidth, cropHeight, GraphicsUnit.Pixel);
                    Image displayImage = new Bitmap(b, maxWidth, maxHeight);
                    SaveImage(displayImage, newFileName, GetCodecInfo("image/" + GetFormat(newFileName).ToString().ToLower()));
                    return true;
                }
            }
            catch (System.Exception e)
            {
                throw e;
            }
            finally
            {
                originalImage.Dispose();
                b.Dispose();
            }
        }
        #endregion

        #region 图片旋转函数
        /// <summary>
        /// 以逆时针为方向对图像进行旋转  Bitmap的用法：http://blog.sina.com.cn/s/blog_4bc3dab30100ccph.html
        /// </summary>
        /// <param name="b">位图流</param>
        /// <param name="angle">旋转角度[0,360](前台给的)</param>
        /// <returns></returns>
        public static Bitmap Rotate(Bitmap b, int angle)
        {
            angle = angle % 360;
            //弧度转换
            double radian = angle * Math.PI / 180.0;
            double cos = Math.Cos(radian);
            double sin = Math.Sin(radian);
            //原图的宽和高
            int w = b.Width;
            int h = b.Height;
            int W = (int)(Math.Max(Math.Abs(w * cos - h * sin), Math.Abs(w * cos + h * sin)));
            int H = (int)(Math.Max(Math.Abs(w * sin - h * cos), Math.Abs(w * sin + h * cos)));
            //目标位图
            Bitmap dsImage = new Bitmap(W, H);
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(dsImage);
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.Bilinear;
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            //计算偏移量
            Point Offset = new Point((W - w) / 2, (H - h) / 2);
            //构造图像显示区域：让图像的中心与窗口的中心点一致
            Rectangle rect = new Rectangle(Offset.X, Offset.Y, w, h);
            Point center = new Point(rect.X + rect.Width / 2, rect.Y + rect.Height / 2);
            g.TranslateTransform(center.X, center.Y);
            g.RotateTransform(360 - angle);
            //恢复图像在水平和垂直方向的平移
            g.TranslateTransform(-center.X, -center.Y);
            g.DrawImage(b, rect);
            //重至绘图的所有变换
            g.ResetTransform();
            g.Save();
            g.Dispose();
            //dsImage.Save("yuancd.jpg", System.Drawing.Imaging.ImageFormat.Jpeg);
            return dsImage;
        }
        #endregion 图片旋转函数
        
    }

通过Base64编码来上传图片的代码如下：

    public class PicHandler : IHttpHandler
    {
        public static string CmdocumentUrl = ConfigurationManager.AppSettings["CmdocumentUrl"];
        public static readonly string BaseDir = ConfigurationManager.AppSettings["BaseDir"];
        
        public void ProcessRequest(HttpContext context)
        {
            if (HttpContext.Current.Request.QueryString["action"] == "action")
            {
                try
                {
                    WeLogHelper.WriteLog("上传图片开始");
                    uppic();
                }
                catch(Exception ex)
                {
                    WeLogHelper.WriteLog(ex.ToString());
                }
              
            }
            context.Response.ContentType = "text/plain";
        }

        protected void uppic()
        {
            //13 代表现场考察打分附件
            DocumentTypeIdEnum keyword = (DocumentTypeIdEnum)Enum.ToObject(typeof(DocumentTypeIdEnum), 13);
            string pic = HttpContext.Current.Request.Form["images"];
            pic = HttpContext.Current.Server.UrlDecode(pic);
            if (pic != null)
            {
                var imgData = pic.Split(',')[1];

                string dummyData = imgData.Trim().Replace("%", "").Replace(",", "").Replace(" ", "+");
                if (dummyData.Length % 4 > 0)
                {
                    dummyData = dummyData.PadRight(dummyData.Length + 4 - dummyData.Length % 4, '=');
                }
                byte[] byteArray = Convert.FromBase64String(dummyData);

                MemoryStream stream = new MemoryStream(byteArray);
                Bitmap image = new Bitmap(stream);
                string kkpath = Guid.NewGuid().ToString();
                string serverPath = BaseDir + "/" + kkpath + "/";
               
                // string serverPath = HttpContext.Current.Server.MapPath(fileurl);

                if (Directory.Exists(serverPath) == false)//如果不存在就创建file文件夹
                {
                    Directory.CreateDirectory(serverPath);
                }

                string picNum = Guid.NewGuid().ToString("N");
                string relativeUri = "/" + kkpath.ToString() + "/" + picNum + ".png"; 
                string url = serverPath + picNum + ".png";
                image.Save(url);
                //
                #region 生成缩略图
                string Uri = BaseDir + relativeUri;
                //缩略图名称
                string SLT_PicName = Guid.NewGuid().ToString("N") + ".png";
                string SLT_url = serverPath + SLT_PicName;
                //WeLogHelper.WriteLog("缩略图：" + SLT_url);
                PicManger.MakeThumbnailImage(url, SLT_url, 100, 100, "Cut");
                //PicManger.SaveImage(bpmImg, SLT_url, PicManger.GetCodecInfo("image/" + PicManger.GetFormat(SLT_PicName).ToString().ToLower()));

                #endregion
                string Base64SR = "data:image/png;base64," + new InspectionRatingSeeModel().ImgToBase64String(SLT_url);
                DocumentM M = new DocumentM()
                {
                    DocumentId=Convert.ToInt64(DateTime.Now.ToString("yyMMddhhmmss")),
                    DocumentName = Path.GetFileName(picNum + ".png"),
                    DocumentPath = serverPath,
                    DocumentTypeId = keyword,
                    CreateUserName = "",
                    Url = relativeUri,
                    Documenttemppath=SLT_url,
                    DocRealPath= CmdocumentUrl + relativeUri,
                    DocBase64SR= Base64SR

                };


               // WeLogHelper.WriteLog("缩略图："+SLT_url);


                var MJson = JsonHelper.JsonSerializer(M);
                //
                //WeLogHelper.WriteLog(MJson);
                HttpContext.Current.Response.Write(MJson);
            }

            HttpContext.Current.Response.End();
        }

        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
    }

生成Base64编码的方法如下：

        public String ImgToBase64String(string fileName)
        {
            FileInfo file = new FileInfo(fileName);
            var stream = file.OpenRead();
            byte[] buffer = new byte[file.Length];
            //读取图片字节流
            stream.Read(buffer, 0, Convert.ToInt32(file.Length));
            //将字节流转化成base64字符串
           return Convert.ToBase64String(buffer);
        }

生成的Base64编码如果想要展示出来，就需要加上前缀，前缀要结合图片的扩展名，如下：

foreach (var item in RatingModel.CmDocumentList)
                    {
                        string Uri = item.Documenttemppath;
                        item.DocBase64SR = "data:image/png;base64,"+ImgToBase64String(Uri);
                        //WeLogHelper.WriteLog(item.DocBase64SR);
                    }

Uri为绝对路径！

前端调用如下：

 <ul>
                                                        <li class="weui-uploader__file" style="background-image:url(@item.DocBase64SR)">
                                                            <div class="weui-uploader__file-content"></div>
                                                        </li>

本博客都是精华！请笑纳！哈哈哈！

谢谢！