第一种
复制代码 代码如下:
/**//// <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 = 0;
int y = 0;
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 = 0;
x = (originalImage.Width - ow)/2;
}
else
{
ow = originalImage.Width;
oh = originalImage.Width*height/towidth;
x = 0;
y = (originalImage.Height - oh)/2;
}
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(0, 0, 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();
}
}

关键方法Graphics.DrawImage见ms-help://MS.NETFrameworkSDKv1.1.CHS/cpref/html/frlrfsystemdrawinggraphicsclassdrawimagetopic11.htm
第二种
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的!
复制代码 代码如下:
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 ilename.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 ilename.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;
}
}
}