ASP.NET C# 按原图片大小等比例缩放生成缩略图

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<%@ Page Language="C#" AutoEventWireup="true" CodeFile="test_img.aspx.cs" Inherits="test_test_img" %> 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml" > 
<head runat="server"> 
<title>缩略图测试</title> 
</head> 
<body style="text-align:center;"> 
<form id="form1" runat="server"> 
原图:<br /> 
<asp:Image ID="Image1" runat="server" /> 
<br /> 
缩略图:<br /> 
<asp:Image ID="Image2" runat="server" /> 
<br /> 
</form> 
</body> 
</html>

以下这个缩略图函数生成后空白部分是用背景色填充的.

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Text;
namespace cha_net.admin
{
    public partial class aa : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            //原图片路径 
            string source = Server.MapPath("~/images/1.jpg");
            string type = "";
            //获取原图片格式 
            string fileExtension = System.IO.Path.GetExtension(source).ToLower();
            switch (fileExtension)
            {
                case ".gif": type = ".gif"; break;
                case ".jpg": type = ".jpg"; break;
                case ".bmp": type = ".bmp"; break;
                case ".png": type = ".png"; break;
            }
            //缩略图保存位置和文件名,图片格式 
            string small = Server.MapPath("~/images/Small/Small_test" + type);
            MakeThumbnail(source, small, 90, 130);
            Image1.ImageUrl = source;
            Image2.ImageUrl = small;
        }
        /**/
        //// <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> 
        public void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height)
        {
            //获取原始图片 
            System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath);
            //缩略图画布宽高 
            int towidth = width;
            int toheight = height;
            //原始图片写入画布坐标和宽高(用来设置裁减溢出部分) 
            int x = 0;
            int y = 0;
            int ow = originalImage.Width;
            int oh = originalImage.Height;
            //原始图片画布,设置写入缩略图画布坐标和宽高(用来原始图片整体宽高缩放) 
            int bg_x = 0;
            int bg_y = 0;
            int bg_w = towidth;
            int bg_h = toheight;
            //倍数变量 
            double multiple = 0;
            //获取宽长的或是高长与缩略图的倍数 
            if (originalImage.Width >= originalImage.Height) multiple = (double)originalImage.Width / (double)width;
            else multiple = (double)originalImage.Height / (double)height;
            //上传的图片的宽和高小等于缩略图 
            if (ow <= width && oh <= height)
            {
                //缩略图按原始宽高 
                bg_w = originalImage.Width;
                bg_h = originalImage.Height;
                //空白部分用背景色填充 
                bg_x = Convert.ToInt32(((double)towidth - (double)ow) / 2);
                bg_y = Convert.ToInt32(((double)toheight - (double)oh) / 2);
            }
            //上传的图片的宽和高大于缩略图 
            else
            {
                //宽高按比例缩放 
                bg_w = Convert.ToInt32((double)originalImage.Width / multiple);
                bg_h = Convert.ToInt32((double)originalImage.Height / multiple);
                //空白部分用背景色填充 
                bg_y = Convert.ToInt32(((double)height - (double)bg_h) / 2);
                bg_x = Convert.ToInt32(((double)width - (double)bg_w) / 2);
            }
            //新建一个bmp图片,并设置缩略图大小. 
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);
            //新建一个画板 
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap);
            //设置高质量插值法 
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBilinear;
            //设置高质量,低速度呈现平滑程度 
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            //清空画布并设置背景色 
            g.Clear(System.Drawing.ColorTranslator.FromHtml("#F2F2F2"));
            //在指定位置并且按指定大小绘制原图片的指定部分 
            //第一个System.Drawing.Rectangle是原图片的画布坐标和宽高,第二个是原图片写在画布上的坐标和宽高,最后一个参数是指定数值单位为像素 
            g.DrawImage(originalImage, new System.Drawing.Rectangle(bg_x, bg_y, bg_w, bg_h), new System.Drawing.Rectangle(x, y, ow, oh), System.Drawing.GraphicsUnit.Pixel);
            try
            {
                //获取图片类型 
                string fileExtension = System.IO.Path.GetExtension(originalImagePath).ToLower();
                //按原图片类型保存缩略图片,不按原格式图片会出现模糊,锯齿等问题. 
                switch (fileExtension)
                {
                    case ".gif": bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Gif); break;
                    case ".jpg": bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg); break;
                    case ".bmp": bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Bmp); break;
                    case ".png": bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Png); break;
                }
            }
            catch (System.Exception e)
            {
                throw e;
            }
            finally
            {
                originalImage.Dispose();
                bitmap.Dispose();
                g.Dispose();
            }
        }
    }
}