App_Code/Upload.cs

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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.Design;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
/// <summary>
/// Upload handler for uploading files.
/// </summary>
public class Upload : IHttpHandler
{
    public Upload()
    {
    }

    #region IHttpHandler Members

    public bool IsReusable
    {
        get { return true; }
    }
    /// <summary>
    /// 产生缩略图
    /// </summary>
    /// <param name="original_image_file">源文件</param>
    /// <param name="object_width">缩略图宽度</param>
    /// <param name="object_height">缩略图高度</param>
    public static void GetThumbnailImage(string original_image_file,string zoom_image_file, int object_width, int object_height)
    {
        int actual_width = 0;
        int actual_heigh = 0;
        string outputfilename = zoom_image_file;

        System.Drawing.Bitmap original_image = new Bitmap(original_image_file);//读取源文件           
        actual_width = original_image.Width;
        actual_heigh = original_image.Height;
        
        Bitmap img = new Bitmap(object_width, object_height);
        img.SetResolution(180f, 180f);
        Graphics gdiobj = Graphics.FromImage(img);
        gdiobj.CompositingQuality = CompositingQuality.HighQuality;
        gdiobj.SmoothingMode = SmoothingMode.HighQuality;
        gdiobj.InterpolationMode = InterpolationMode.HighQualityBicubic;
        gdiobj.PixelOffsetMode = PixelOffsetMode.HighQuality;

        gdiobj.FillRectangle(new SolidBrush(Color.White), 0, 0,object_width, object_height);
        Rectangle destrect = new Rectangle(0, 0,object_width, object_height);

        gdiobj.DrawImage(original_image, destrect, 0, 0, actual_width,actual_heigh, GraphicsUnit.Pixel);

        System.Drawing.Imaging.EncoderParameters ep = new System.Drawing.Imaging.EncoderParameters(1);
        ep.Param[0] = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, (long)100);