图片 生成缩略图

using System;
using System.Web;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.Drawing.Imaging;
using System.Data.OleDb;

/// <summary>
 /// thumbnailimage 的摘要说明。
 /// </summary>
 public class thumbnailimage
 {
  /// <summary>
  /// /**//// <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>
  /// thumbnailimage 的摘要说明
  /// </summary>
  ///
  public thumbnailimage(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 "WH"://按指定宽高自适应大小
     if((double)originalImage.Width / (double)originalImage.Height > 1.00)
     {
                      toheight = originalImage.Height * width / originalImage.Width;
     }
     else
     {
                       towidth = originalImage.Width * height / originalImage.Height; 
     }
     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();
   }
  }
 }