.net自带的生成缩略图的方法是Bitmap.GetThumbnailImage这个方法生成的缩略图不够清晰，一般我们会使用 Graphics高质量插值发生成清晰的缩略图，这时候大小会不尽人意，怎么办？我们可以使用jpeg压缩的方法压缩一下图片，这样图片的大小会缩小到压 缩前的十分之一。

下面是完成这项工作的代码：

using System;  using System.Collections.Generic;  using System.Linq;  using System.Text;  using System.Drawing;  using System.IO;    namespace ConsoleApplication3_ThumbnailImg  {      class Program      {          const int HEIGHT = 190;          const int WIDTH = 190;          static void Main(string[] args)          {              string srcImgPath = @"G:\photoes\20060725\Picture 057.jpg";              string targetFolder = @"E:\Diary\Test\thumbnail";                SetThumbnail_1(srcImgPath, targetFolder);              SetThumbnail_2(srcImgPath, targetFolder);              SetThumbnail_3(srcImgPath, targetFolder);                Console.Read();          }            static void SetThumbnail_1(string srcImgPath, string targetFolder)          {              using (Bitmap source = new Bitmap(srcImgPath))              {                  // return the source image if it's smaller than the designated thumbnail                     int wi, hi;                  wi = WIDTH;                  hi = HEIGHT;                    // maintain the aspect ratio despite the thumbnail size parameters                     if (source.Width > source.Height)                  {                      wi = WIDTH;                      hi = (int)(source.Height * ((decimal)WIDTH / source.Width));                  }                  else                  {                      hi = HEIGHT;                      wi = (int)(source.Width * ((decimal)HEIGHT / source.Height));                  }                    using (Image thumb = source.GetThumbnailImage(wi, hi, null, IntPtr.Zero))                  {                      string targetPath = Path.Combine(targetFolder, "th_1.jpg");                      thumb.Save(targetPath);                  }              }          }            static void SetThumbnail_2(string srcImgPath, string targetFolder)          {              using (Bitmap source = new Bitmap(srcImgPath))              {                  // return the source image if it's smaller than the designated thumbnail                     int wi, hi;                  wi = WIDTH;                  hi = HEIGHT;                    // maintain the aspect ratio despite the thumbnail size parameters                     if (source.Width > source.Height)                  {                      wi = WIDTH;                      hi = (int)(source.Height * ((decimal)WIDTH / source.Width));                  }                  else                  {                      hi = HEIGHT;                      wi = (int)(source.Width * ((decimal)HEIGHT / source.Height));                  }                    // original code that creates lousy thumbnails                     // System.Drawing.Image ret = source.GetThumbnailImage(wi,hi,null,IntPtr.Zero);                     using (System.Drawing.Bitmap thumb = new Bitmap(wi, hi))                  {                      using (Graphics g = Graphics.FromImage(thumb))                      {                          g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;                          g.FillRectangle(Brushes.White, 0, 0, wi, hi);                          g.DrawImage(source, 0, 0, wi, hi);                      }                      string targetPath = Path.Combine(targetFolder, "th_2.jpg");                      thumb.Save(targetPath);                  }                }          }            static void SetThumbnail_3(string srcImgPath, string targetFolder)          {              //Configure JPEG Compression Engine                 System.Drawing.Imaging.EncoderParameters encoderParams = new System.Drawing.Imaging.EncoderParameters();              long[] quality = new long[1];              quality[0] = 75;              System.Drawing.Imaging.EncoderParameter encoderParam = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);              encoderParams.Param[0] = encoderParam;                System.Drawing.Imaging.ImageCodecInfo[] arrayICI = System.Drawing.Imaging.ImageCodecInfo.GetImageEncoders();              System.Drawing.Imaging.ImageCodecInfo jpegICI = null;              for (int x = 0; x < arrayICI.Length; x++)              {                  if (arrayICI[x].FormatDescription.Equals("JPEG"))                  {                      jpegICI = arrayICI[x];                      break;                  }              }                using (Bitmap source = new Bitmap(srcImgPath))              {                  int wi, hi;                  wi = WIDTH;                  hi = HEIGHT;                    // maintain the aspect ratio despite the thumbnail size parameters                     if (source.Width > source.Height)                  {                      wi = WIDTH;                      hi = (int)(source.Height * ((decimal)WIDTH / source.Width));                  }                  else                  {                      hi = HEIGHT;                      wi = (int)(source.Width * ((decimal)HEIGHT / source.Height));                  }                    // original code that creates lousy thumbnails                     // System.Drawing.Image ret = source.GetThumbnailImage(wi,hi,null,IntPtr.Zero);                     using (System.Drawing.Bitmap thumb = new Bitmap(wi, hi))                  {                      using (Graphics g = Graphics.FromImage(thumb))                      {                          g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;                          g.FillRectangle(Brushes.White, 0, 0, wi, hi);                          g.DrawImage(source, 0, 0, wi, hi);                      }                      string targetPath = Path.Combine(targetFolder, "th_3.jpg");                      thumb.Save(targetPath, jpegICI, encoderParams);                  }                }            }      }  }