Passing parameters to a page

I am dynamically generating an image as shown below. How can I pass parameters to the ImageGen.aspx code from Default.aspx so that the image can be constructed based on that.

  //File:ImageGen.aspx
    public partial class ImageGen: System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            Bitmap image = new Bitmap(800, 400);
            //Code to generate image
            image.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
        }
    }

This image is displayed by:

 //File: De开发者_如何学运维fault.aspx
 protected void Page_Load(object sender, EventArgs e)
 {
      Image1.ImageUrl = "~/ImageGen.aspx";
 }

You can pass values to page using query string parameters i.e. in default.aspx call image generator page:

Image1.ImageUrl = "~/ImageGen.aspx?imageId=1";

and in Page_Load method of ImageGen.aspx retrieve this using

string imageId = Request.QueryString["imageId"];

You need to read about State Maintenance in ASP.NET

Right now for your case Make use of Request query stirng that it

 //File: Default.aspx
 protected void Page_Load(object sender, EventArgs e)
 {
      Image1.ImageUrl = "~/ImageGen.aspx?id=1";
 }

in second code use it

 //File:ImageGen.aspx
    public partial class ImageGen: System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            string id = Request.QueryString["id"];
            Bitmap image = new Bitmap(800, 400);
            //Code to generate image
            image.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
        }
    }