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