代碼如下:

using System; 
using System.Data; 
using System.Configuration; 
using System.Web; 
using System.Web.Security; 
using System.Web.UI; 
using System.Web.UI.WebControls; 
using System.Web.UI.WebControls.WebParts; 
using System.Web.UI.HtmlControls; 
using System.IO; 
using System.Drawing; 
using System.Drawing.Imaging; 

/// <summary> 
/// 圖片處理類 
/// 1、生成縮略圖片或按照比例改變圖片的大小和畫質 
/// 2、將生成的縮略圖放到指定的目錄下 
/// </summary> 
public class ImageClass 
{ 
public System.Drawing.Image ResourceImage; 
private int ImageWidth; 
private int ImageHeight; 

public string ErrMessage; 

/// <summary> 
/// 類的構造函數 
/// </summary> 
/// <param name="ImageFileName">圖片文件的全路徑名稱</param> 
public ImageClass(string ImageFileName) 
{ 
ResourceImage = System.Drawing.Image.FromFile(ImageFileName); 
ErrMessage = ""; 
} 

public bool ThumbnailCallback() 
{ 
return false; 
} 

/// <summary> 
/// 生成縮略圖重載方法1，返回縮略圖的Image對象 
/// </summary> 
/// <param name="Width">縮略圖的寬度</param> 
/// <param name="Height">縮略圖的高度</param> 
/// <returns>縮略圖的Image對象</returns> 
public System.Drawing.Image GetReducedImage(int Width, int Height) 
{ 
try 
{ 
System.Drawing.Image ReducedImage; 

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

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

return ReducedImage; 
} 
catch (Exception e) 
{ 
ErrMessage = e.Message; 
return null; 
} 
} 

/// <summary> 
/// 生成縮略圖重載方法2，將縮略圖文件保存到指定的路徑 
/// </summary> 
/// <param name="Width">縮略圖的寬度</param> 
/// <param name="Height">縮略圖的高度</param> 
/// <param name="targetFilePath">縮略圖保存的全文件名，(帶路徑)，參數格式：D:Images ilename.jpg</param> 
/// <returns>成功返回true，否則返回false</returns> 
public bool GetReducedImage(int Width, int Height, string targetFilePath) 
{ 
try 
{ 
System.Drawing.Image ReducedImage; 

System.Drawing.Image.GetThumbnailImageAbort callb = new System.Drawing.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> 
/// 生成縮略圖重載方法3，返回縮略圖的Image對象 
/// </summary> 
/// <param name="Percent">縮略圖的寬度百分比 如：需要百分之80，就填0.8</param> 
/// <returns>縮略圖的Image對象</returns> 
public System.Drawing.Image GetReducedImage(double Percent) 
{ 
try 
{ 
System.Drawing.Image ReducedImage; 

System.Drawing.Image.GetThumbnailImageAbort callb = new System.Drawing.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> 
/// 生成縮略圖重載方法4，返回縮略圖的Image對象 
/// </summary> 
/// <param name="Percent">縮略圖的寬度百分比 如：需要百分之80，就填0.8</param> 
/// <param name="targetFilePath">縮略圖保存的全文件名，(帶路徑)，參數格式：D:Images ilename.jpg</param> 
/// <returns>成功返回true,否則返回false</returns> 
public bool GetReducedImage(double Percent, string targetFilePath) 
{ 
try 
{ 
System.Drawing.Image ReducedImage; 

System.Drawing.Image.GetThumbnailImageAbort callb = new System.Drawing.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; 
} 
} 
}