C#生成缩略图的方法

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;
             }
         }

     }

 }