请问如何把数据库中的图片读出生成缩略图?sql server+c#.net)
用的控件是datlist
我就是想是缩略图来显示

using System;
using System.Collections.Generic;
using System.Text;
using
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;

namespace Common
{
    /// <summary>
    /// 图片缩略图处理类
    /// </summary>
    public class Thumbnail
    {
        /// <summary>
        /// 局部私有变量
        /// </summary>
        private Image srcImage;
        private string srcFileName;
        public Image ResourceImage;
        private int ImageWidth;
        private int ImageHeight;
        public string ErrorMessage;

        /// <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 ((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(System.Drawing.Imaging.Encoder.Quality, ((long)90));
            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)
        {
            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="fileName">原图的文件路径</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)
        {
            Image image = Image.FromFile(fileName);

            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);
                g.InterpolationMode = InterpolationMode.High;
                g.SmoothingMode = SmoothingMode.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/jpeg"));
            }
            finally
            {
                image.Dispose();
                b.Dispose();
            }
        }


        /// <summary>
        /// 制作缩略图
        /// </summary>
        /// <param name="fileName">原图路径</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)
        {
            Image original = Image.FromFile(fileName);

            Size _newSize = ResizeImage(original.Width, original.Height, maxWidth, maxHeight);
            //_image.Height = _newSize.Height;
            //_image.Width = _newSize.Width;
            Image displayImage = new Bitmap(original, _newSize);
            original.Dispose();

            try
            {
                displayImage.Save(newFileName, GetFormat(fileName));

            }
            finally
            {
                original.Dispose();
            }
        }

        /// <summary>
        /// 按大小生成缩略图
        /// </summary>
        /// <param name="Width">宽度</param>
        /// <param name="Height">高度</param>
        /// <param name="targetFilePath">陆军</param>
        /// <returns></returns>
        public bool ReducedImage(int Width, int Height, string targetFilePath)
        {
            try
            {
                Image ReducedImage;
                Image.GetThumbnailImageAbort callb = new Image.GetThumbnailImageAbort(ThumbnailCallback);
                ReducedImage = ResourceImage.GetThumbnailImage(Width, Height, callb, IntPtr.Zero);
                ReducedImage.Save(@targetFilePath, ImageFormat.Jpeg);
                ReducedImage.Dispose();
                return true;
            }
            catch (Exception e)
            {
                ErrorMessage = e.Message;
                return false;
            }
        }

        /// <summary>
        /// 按百分比  缩小60% Percent为0.6 targetFilePath为目标路径
        /// </summary>
        /// <param name="Percent">图片比例</param>
        /// <param name="targetFilePath">路径</param>
        /// <returns></returns>
        public bool ReducedImage(double Percent, string targetFilePath)
        {
            try
            {
                Image ReducedImage;
                Image.GetThumbnailImageAbort callb = new Image.GetThumbnailImageAbort(ThumbnailCallback);
                ImageWidth = Convert.ToInt32(ResourceImage.Width * Percent);
                ImageHeight = (ResourceImage.Height) * ImageWidth / ResourceImage.Width;//等比例缩放
                ReducedImage = ResourceImage.GetThumbnailImage(ImageWidth, ImageHeight, callb, IntPtr.Zero);
                ReducedImage.Save(@targetFilePath, ImageFormat.Jpeg);
                ReducedImage.Dispose();
                return true;
            }
            catch (Exception e)
            {
                ErrorMessage = e.Message;
                return false;
            }
        }
    }
}

'功能缩放图片，并保存缩放后的图片，长宽比不变
  '入口：
  'strSourceImagePath：原图片位置
  'intWidth：目标图片的宽度
  'intHeight：目标图片的高度
  'strDecImagePath：目标图片存放的位置
  Public Sub imageZoom(ByVal strSourceImagePath As String, ByVal intWidth As Integer, ByVal intHeight As String, ByVal strDecImagePath As String)
    Dim imageSource As Image = New Bitmap(strSourceImagePath)
    Dim intimageSourceWidth As Integer = imageSource.Width '读取原图片的宽度
    Dim intimageSourceHeight As Integer = imageSource.Height '读取原图片的高度
    Dim singleZoom As Single

    If (intWidth / intimageSourceWidth) <= (intHeight / intimageSourceHeight) Then '宽度比高度大，则以宽度计算缩放比例
      singleZoom = intWidth / intimageSourceWidth
    Else
      singleZoom = intHeight / intimageSourceHeight
    End If

    Dim imageDec As Image = New Bitmap(imageSource, intimageSourceWidth * singleZoom, intimageSourceHeight * singleZoom)
    imageDec.Save(strDecImagePath, System.Drawing.Imaging.ImageFormat.Jpeg) '保存图片

    imageDec.Dispose()
    imageSource.Dispose()
  End Sub