1、需要添加应用System.Drawing.dll

2.命名空间

using System.IO;

using System.Drawing;

using System.Drawing.Imaging;

3、方法一

**//// <summary>

       /// 生成缩略图

       /// </summary>

       /// <param name="originalImagePath">源图路径（物理路径）</param>

       /// <param name="thumbnailPath">缩略图路径（物理路径）</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 MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)

       {

           Image originalImage = Image.FromFile(originalImagePath); 

           int towidth = width;

           int toheight = height; 

           int x = ;

           int y = ;

           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 = ;

                       x = (originalImage.Width - ow)/;

                   }

                   else

                   {

                       ow = originalImage.Width;

                       oh = originalImage.Width*height/towidth;

                       x = ;

                       y = (originalImage.Height - oh)/;

                   }

                   break;

               default :

                   break;

           }     

           //新建一个bmp图片

           Image bitmap = new System.Drawing.Bitmap(towidth,toheight); 

           //新建一个画板

           Graphics g = System.Drawing.Graphics.FromImage(bitmap); 

           //设置高质量插值法

           g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High; 

           //设置高质量,低速度呈现平滑程度

           g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.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(, , towidth, toheight),

               new Rectangle(x, y, ow,oh),

               GraphicsUnit.Pixel); 

           try

           {

               //以jpg格式保存缩略图

               bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);

           }

           catch(System.Exception e)

           {

               throw e;

           }

           finally

           {

               originalImage.Dispose();

               bitmap.Dispose();

               g.Dispose();

           }

       }

4、方法二

using System.IO;

using System.Drawing;

using System.Drawing.Imaging;

/// <summary>

/// 图片处理类

/// 1、生成缩略图片或按照比例改变图片的大小和画质

/// 2、将生成的缩略图放到指定的目录下

/// </summary>

public class ImageClass

{

    public Image ResourceImage;

    private int ImageWidth;

    private int ImageHeight;

    public string ErrMessage;

    /// <summary>

    /// 类的构造函数

    /// </summary>

    /// <param name="ImageFileName">图片文件的全路径名称</param>

    public ImageClass(string ImageFileName)

    {

        ResourceImage=Image.FromFile(ImageFileName);

     ErrMessage="";

    }

    public bool ThumbnailCallback()

    {

     return false;

    }

    /// <summary>

    /// 生成缩略图重载方法1，返回缩略图的Image对象

    /// </summary>

    /// <param name="Width">缩略图的宽度</param>

    /// <param name="Height">缩略图的高度</param>

    /// <returns>缩略图的Image对象</returns>

    public Image GetReducedImage(int Width,int Height)

    {

     try

     {

      Image ReducedImage;

      Image.GetThumbnailImageAbort callb=new Image.GetThumbnailImageAbort(ThumbnailCallback); 

      ReducedImage=ResourceImage.GetThumbnailImage(Width,Height,callb,IntPtr.Zero);

      return ReducedImage;

     }

     catch(Exception e)

     {

      ErrMessage=e.Message;

         return null;

     }

    }

    /// <summary>

    /// 生成缩略图重载方法2，将缩略图文件保存到指定的路径

    /// </summary>

    /// <param name="Width">缩略图的宽度</param>

    /// <param name="Height">缩略图的高度</param>

    /// <param name="targetFilePath">缩略图保存的全文件名，(带路径)，参数格式：D:\Images\filename.jpg</param>

    /// <returns>成功返回true，否则返回false</returns>

    public bool GetReducedImage(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)

     {

      ErrMessage=e.Message;

      return false;

     }

    }

    /// <summary>

    /// 生成缩略图重载方法3，返回缩略图的Image对象

    /// </summary>

    /// <param name="Percent">缩略图的宽度百分比 如：需要百分之80，就填0.8</param>

    /// <returns>缩略图的Image对象</returns>

    public Image GetReducedImage(double Percent)

    {

     try

     {

      Image ReducedImage;

      Image.GetThumbnailImageAbort callb=new Image.GetThumbnailImageAbort(ThumbnailCallback);

      ImageWidth=Convert.ToInt32(ResourceImage.Width*Percent);

      ImageHeight=Convert.ToInt32(ResourceImage.Width*Percent);

      ReducedImage=ResourceImage.GetThumbnailImage(ImageWidth,ImageHeight,callb,IntPtr.Zero);

      return ReducedImage;

     }

     catch(Exception e)

     {

      ErrMessage=e.Message;

      return null;

     }

    }

    /// <summary>

    /// 生成缩略图重载方法4，返回缩略图的Image对象

    /// </summary>

    /// <param name="Percent">缩略图的宽度百分比 如：需要百分之80，就填0.8</param>

    /// <param name="targetFilePath">缩略图保存的全文件名，(带路径)，参数格式：D:\Images\filename.jpg</param>

    /// <returns>成功返回true,否则返回false</returns>

    public bool GetReducedImage(double Percent,string targetFilePath)

    {

     try

     {

      Image ReducedImage;

      Image.GetThumbnailImageAbort callb=new Image.GetThumbnailImageAbort(ThumbnailCallback);

      ImageWidth=Convert.ToInt32(ResourceImage.Width*Percent);

      ImageHeight=Convert.ToInt32(ResourceImage.Width*Percent);

      ReducedImage=ResourceImage.GetThumbnailImage(ImageWidth,ImageHeight,callb,IntPtr.Zero);

      ReducedImage.Save(@targetFilePath,ImageFormat.Jpeg);

      ReducedImage.Dispose(); 

      return true;

     }

     catch(Exception e)

     {

      ErrMessage=e.Message;

      return false;

     }

    }

}

5、亲测可用

 using System;

 using System.Collections.Generic;

 using System.Linq;

 using System.Text;

 using System.IO;

 using System.Drawing;

 using System.Drawing.Imaging;

 namespace ConsoleApplication2

 {

     class Program

     {

         static void Main(string[] args)

         {

             string originalImagePath ="D:/pic/2012cnu-gisBarbecue/IMG_7226.JPG";

             string thumbnailPath ="D:/pic/2012cnu-gisBarbecue/14.jpg";

             MakeThumbnail(originalImagePath, thumbnailPath, , , "W");

             thumbnailPath = "D:/pic/2012cnu-gisBarbecue/15.jpg";

             ImageClass imageC = new ImageClass(originalImagePath);

             imageC.GetReducedImage(0.5, thumbnailPath);

         }

         /**/

         /// <summary>

         /// 生成缩略图

         /// </summary>

         /// <param name="originalImagePath">源图路径（物理路径）</param>

         /// <param name="thumbnailPath">缩略图路径（物理路径）</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 MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)

         {

             Image originalImage = Image.FromFile(originalImagePath);

             int towidth = width;

             int toheight = height;

             int x = ;

             int y = ;

             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 = ;

                         x = (originalImage.Width - ow) / ;

                     }

                     else

                     {

                         ow = originalImage.Width;

                         oh = originalImage.Width * height / towidth;

                         x = ;

                         y = (originalImage.Height - oh) / ;

                     }

                     break;

                 default:

                     break;

             }

             //新建一个bmp图片

             Image bitmap = new System.Drawing.Bitmap(towidth, toheight);

             //新建一个画板

             Graphics g = System.Drawing.Graphics.FromImage(bitmap);

             //设置高质量插值法

             g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

             //设置高质量,低速度呈现平滑程度

             g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.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(, , towidth, toheight),

                 new Rectangle(x, y, ow, oh),

                 GraphicsUnit.Pixel);

             try

             {

                 //以jpg格式保存缩略图

                 bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);

             }

             catch (System.Exception e)

             {

                 throw e;

             }

             finally

             {

                 originalImage.Dispose();

                 bitmap.Dispose();

                 g.Dispose();

             }

         }

     }

     public class ImageClass

     {

         public Image ResourceImage;

         private int ImageWidth;

         private int ImageHeight;

         public string ErrMessage;

         /// <summary>

         /// 类的构造函数

         /// </summary>

         /// <param name="ImageFileName">图片文件的全路径名称</param>

         public ImageClass(string ImageFileName)

         {

             ResourceImage = Image.FromFile(ImageFileName);

             ErrMessage = "";

         }

         public bool ThumbnailCallback()

         {

             return false;

         }

         /// <summary>

         /// 生成缩略图重载方法1，返回缩略图的Image对象

         /// </summary>

         /// <param name="Width">缩略图的宽度</param>

         /// <param name="Height">缩略图的高度</param>

         /// <returns>缩略图的Image对象</returns>

         public Image GetReducedImage(int Width, int Height)

         {

             try

             {

                 Image ReducedImage;

                 Image.GetThumbnailImageAbort callb = new Image.GetThumbnailImageAbort(ThumbnailCallback);

                 ReducedImage = ResourceImage.GetThumbnailImage(Width, Height, callb, IntPtr.Zero);

                 return ReducedImage;

             }

             catch (Exception e)

             {

                 ErrMessage = e.Message;

                 return null;

             }

         }

         /// <summary>

         /// 生成缩略图重载方法2，将缩略图文件保存到指定的路径

         /// </summary>

         /// <param name="Width">缩略图的宽度</param>

         /// <param name="Height">缩略图的高度</param>

         /// <param name="targetFilePath">缩略图保存的全文件名，(带路径)，参数格式：D:\Images\filename.jpg</param>

         /// <returns>成功返回true，否则返回false</returns>

         public bool GetReducedImage(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)

             {

                 ErrMessage = e.Message;

                 return false;

             }

         }

         /// <summary>

         /// 生成缩略图重载方法3，返回缩略图的Image对象

         /// </summary>

         /// <param name="Percent">缩略图的宽度百分比 如：需要百分之80，就填0.8</param>

         /// <returns>缩略图的Image对象</returns>

         public Image GetReducedImage(double Percent)

         {

             try

             {

                 Image ReducedImage;

                 Image.GetThumbnailImageAbort callb = new Image.GetThumbnailImageAbort(ThumbnailCallback);

                 ImageWidth = Convert.ToInt32(ResourceImage.Width * Percent);

                 ImageHeight = Convert.ToInt32(ResourceImage.Width * Percent);

                 ReducedImage = ResourceImage.GetThumbnailImage(ImageWidth, ImageHeight, callb, IntPtr.Zero);

                 return ReducedImage;

             }

             catch (Exception e)

             {

                 ErrMessage = e.Message;

                 return null;

             }

         }

         /// <summary>

         /// 生成缩略图重载方法4，返回缩略图的Image对象

         /// </summary>

         /// <param name="Percent">缩略图的宽度百分比 如：需要百分之80，就填0.8</param>

         /// <param name="targetFilePath">缩略图保存的全文件名，(带路径)，参数格式：D:\Images\filename.jpg</param>

         /// <returns>成功返回true,否则返回false</returns>

         public bool GetReducedImage(double Percent, string targetFilePath)

         {

             try

             {

                 Image ReducedImage;

                 Image.GetThumbnailImageAbort callb = new Image.GetThumbnailImageAbort(ThumbnailCallback);

                 ImageWidth = Convert.ToInt32(ResourceImage.Width * Percent);

                 ImageHeight = Convert.ToInt32(ResourceImage.Width * Percent);

                 ReducedImage = ResourceImage.GetThumbnailImage(ImageWidth, ImageHeight, callb, IntPtr.Zero);

                 ReducedImage.Save(@targetFilePath, ImageFormat.Jpeg);

                 ReducedImage.Dispose();

                 return true;

             }

             catch (Exception e)

             {

                 ErrMessage = e.Message;

                 return false;

             }

         }

     }

 }

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