C#生成图片缩略图(2种思路)

前言：在日常图片浏览中，如果图片过多，只有一张张的打开图片才能知道图片的内容，显然这样浏览起来非常不便。Windows系统在浏览图片时提供了缩略图的功能，这样大大的方便了浏览者了解每张图片的内容，本实例采用两种方式实现了与Windows系统缩略图相同的功能。

第一种：生成MakeThumbnail方法

 //// <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();
     }
  }

 ThumbnailClass

MakeThumbnail

第二种：写成ThumbnailClass类，书写4个重载方法,有直接返回Image对象的,有生成缩略图,并且保存到指定目录等等

 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;
      }
     }
 }

ThumbnailClass