如何在ASP.NET页面中自动生成并显示透明的GIF图片

在页面中加入一个图片控件，并将它的Style属性设为：FILTER: chroma(color:#000000) ，原因是自动生成的GIF图片总是黑色背景。然后在后台代码中写入如下代码。(见DEMO)
using System; using System.Collections; using System.ComponentModel; using System.Data; using System.Drawing; using System.Web; using System.Web.SessionState; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.HtmlControls; using System.IO; using System.Drawing.Drawing2D; namespace WebPageIndex { /**//// <summary> /// WebForm1 的摘要说明。 /// </summary> public class WebForm1 : System.Web.UI.Page { protected System.Web.UI.HtmlControls.HtmlImage IMG1; private void Page_Load(object sender, System.EventArgs e) { // 在此处放置用户代码以初始化页面 MyTempImage myTempImage=new MyTempImage(); IMG1.Src=myTempImage.CreateImage(); } public class MyTempImage : Page { public string CreateImage() { string str="兴中公司财务章"; Bitmap image=new Bitmap(300,300); Graphics g=Graphics.FromImage(image); string thefullname=Server.MapPath("/")+"//nowtime.gif"; Pen p=new Pen(Brushes.Red,10); Pen p1=new Pen(Brushes.Red,5); SolidBrush b=new SolidBrush(Color.Red); g.SmoothingMode=SmoothingMode.AntiAlias; Point point1 = new Point( 150, 50); Point point2 = new Point(50, 150); Point point3 = new Point(230, 150); Point[] curvePoints = { point1, point2, point3, }; g.FillPolygon(b,curvePoints,FillMode.Winding ); g.DrawEllipse(p,10,10,280,280); g.DrawString(str,new Font("隶书",20,FontStyle.Bold),new SolidBrush(Color.FromArgb(255, 255,0, 0)),40,200); g.DrawLine(p1,80,240,220,240); g.DrawLine(p1,80,250,220,250); image.Save(thefullname,System.Drawing.Imaging.ImageFormat.Gif); return "/nowtime.gif"; } } Web 窗体设计器生成的代码#region Web 窗体设计器生成的代码 override protected void OnInit(EventArgs e) { // // CODEGEN: 该调用是 ASP.NET Web 窗体设计器所必需的。 // InitializeComponent(); base.OnInit(e); } /**//// <summary> /// 设计器支持所需的方法 - 不要使用代码编辑器修改 /// 此方法的内容。 /// </summary> private void InitializeComponent() { this.Load += new System.EventHandler(this.Page_Load); } #endregion } }

(source:http://www.cnblogs.com/ahuang1118/archive/2005/05/27/163614.html)