说明：本文实现了
图片格式随意转换（下拉框选择）；
点击FileUpload立即显示图片（Js实现）的技巧；
第一步：打开页面
第二步：选择一副Jpg格式的图片
第三步：转换为GIF格式，明显看出图片画质降低。
后台代码：
1
using System;
2using System.Data;
3using System.Configuration;
4using System.Collections;
5using System.Web;
6using System.Web.Security;
7using System.Web.UI;
8using System.Web.UI.WebControls;
9using System.Web.UI.WebControls.WebParts;
10using System.Web.UI.HtmlControls;
11using System.IO;
12using System.Drawing;
13public partial class _Default : System.Web.UI.Page
14
{
15
protected void Page_Load(object sender, EventArgs e)
16
{
17
}
18 protected void Button1_Click(object sender, EventArgs e)
19 {
20 string filepath = FileUpload1.PostedFile.FileName;
21 string filename = filepath.Substring(filepath.LastIndexOf("\") + 1);
22 string serverpath = Server.MapPath("images/") + System.DateTime.Now.ToString("yyy-MM-dd-hh-mm-ss") + Session.SessionID + filename;
23
24 if (DropDownList1.SelectedValue == "GIF")
25 {
26 ConvertImage(FileUpload1.PostedFile.FileName, System.Drawing.Imaging.ImageFormat.Gif, serverpath+".gif");
27 }
28 else if(DropDownList1.SelectedValue == "Jpeg")
29 {
30 ConvertImage(FileUpload1.PostedFile.FileName, System.Drawing.Imaging.ImageFormat.Jpeg, serverpath + ".jpg");
31 }
32 else if(DropDownList1.SelectedValue == "Bmp")
33 {
34 ConvertImage(FileUpload1.PostedFile.FileName, System.Drawing.Imaging.ImageFormat.Bmp, serverpath + ".bmp");
35 }
36 else
37 {
38 //清清月儿留给大家
39 }
40 }
41
42 public void ConvertImage(string Filename, System.Drawing.Imaging.ImageFormat DesiredFormat, string NewFilename)
43 {
44 try
45 {
46 System.Drawing.Image imgFile = System.Drawing.Image.FromFile(Filename);
47 imgFile.Save(NewFilename, DesiredFormat);
48 Image1.ImageUrl = NewFilename;
49 Label1.Text = "转换成功，生成"+NewFilename+"，如下所示。";
50 TextBox1.Text = "1";//开始为0，转换后为1
51 }
52 catch (Exception ex)
53 {
54 Response.Write(ex);
55 }
56 }
57
}
58
前台代码：
1<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
2
3<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
4
5<html xmlns="http://www.w3.org/1999/xhtml" >
6<head runat="server">
7 <title>图片格式转换</title>
8 <script language="javascript">
9 function show_img()//实现选择图片后立即显示给客户
10 {
11 if(document.all.TextBox1.value=="0"){//开始为0，转换后为1
12 document.all.Image1.src=document.all.FileUpload1.value;
13 }
14 else if(document.all.TextBox1.value=="1")
15 {
16 }
17 }
18 </script>
19</head>
20<body>
21 <form id="form1" runat="server">
22 <div>
23
24 <table>
25 <tr>
26 <td style="width: 124px">
27 <asp:FileUpload ID="FileUpload1" runat="server" onmouseover="show_img()" Width="349px"/>
28 </td>
29 <td style="width: 100px">
30 格式<asp:DropDownList ID="DropDownList1" runat="server">
31 <asp:ListItem>GIF</asp:ListItem>
32 <asp:ListItem>Jpeg</asp:ListItem>
33 <asp:ListItem>Bmp</asp:ListItem>
34 <asp:ListItem>Png</asp:ListItem>
35 <asp:ListItem>Ico</asp:ListItem>
36 </asp:DropDownList>
37 </td>
38 <td style="width: 100px">
39 <asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="转换" /></td>
40 <td style="width: 100px">
41 <asp:TextBox ID="TextBox1" runat="server">0</asp:TextBox>
42 </td>
43 </tr>
44 <tr>
45 <td colspan="4">
46 <asp:Label ID="Label1" runat="server"></asp:Label></td>
47 </tr>
48 <tr>
49 <td style="height: 26px;" colspan="4">
50 <asp:Image ID="Image1" runat="server" /></td>
51 </tr>
52 </table>
53
54 </div>
55 </form>
56</body>
57</html>
58
59