How to Pass an Image from Flash to ASP.NET


Quick version:

How do I get an image that was generated on the users browser back to the server?

The current plan is this:

  1. The Flash developer will convert the bitmap to JPEG
  2. He will then POST the JPEG to a page on the site.
  3. I'm thinking I can create a WebService which will use a StreamReader to read the post and save it as a file.

Would that work? Any existing code/samples for doing this?

I suppose we should be able to look at code for doing any file upload to ASP.NET.

Best Solution

In this example, I've created a Flash file with a button on the stage. When you click that button, the Flash sends the image of the button to an ASPX file which saves it out as a JPEG. As you'll see this is done by drawing the DisplayObject into a BitmapData object and as such, you can easily replace the reference to the button with anything that inherits from DisplayObject (including a movie clip that contains the canvas for a paint application etc).

I’ll walk you through the Flash element first and then the .NET backend.


To send a generated image like this from Flash to ASP.NET (or any other backend) you’re going to need a couple of 3rd party libraries. We’ll need a JPEG Encoder (which Flash doesn’t have, but recent versions of Flex do) which we can get from the AS3 Core Lib We’ll also need a base64 encoder for sending the data over the wire. I’ll use the one from Dynamic Flash, available at

Download these and extract them somewhere sensible on your hard disk (like a C:\lib folder).

I created a new AS3 Flash file and saved it as uploader.fla. I added a button component to the stage and named it btnUpload. Next I edited the ActionScript settings and added my c:\lib folder to the classpath. Then I gave the document a class name of Uploader and saved the file.

Next, I created an ActionScript file and added the following code to it:

    import flash.display.BitmapData;
    import flash.display.MovieClip;
    import flash.utils.ByteArray;
    import fl.controls.Button;
    import com.adobe.images.JPGEncoder;
    import com.dynamicflash.util.Base64;

    public class Uploader extends MovieClip
        // Reference to the button on the stage
        public var btnUpload:Button;

        // Encoder quality
        private var _jpegQuality:int = 100;

        // Path to the upload script
        private var _uploadPath:String = "/upload.aspx";

        public function Uploader()
             btnUpload.addEventListener(MouseEvent.CLICK, buttonClick);

        private function buttonClick(e:MouseEvent):void
            // Create a new BitmapData object the size of the upload button.
            // We're going to send the image of the button to the server.
            var image:BitmapData = new BitmapData(btnUpload.width, btnUpload.height);

            // Draw the button into the BitmapData

            // Encode the BitmapData into a ByteArray
            var enc:JPGEncoder = new JPGEncoder(_jpegQuality);
            var bytes:ByteArray = enc.encode(image);

            // and convert the ByteArray to a Base64 encoded string
            var base64Bytes:String = Base64.encodeByteArray(bytes);

            // Add the string to a URLVariables object
            var vars:URLVariables = new URLVariables();
            vars.imageData = base64Bytes;

            // and send it over the wire via HTTP POST
            var url:URLRequest = new URLRequest(_uploadPath);
   = vars;
            url.method = URLRequestMethod.POST;

            var loader:URLLoader = new URLLoader();

I saved this file next to the FLA with the name

I published the SWF into the root of my Asp.NET website. This code assumes you want to upload the jpeg with a quality of 100% and that the script which will receive the data is called upload.aspx and is located in the root of the site.


In the root of my website I created a WebForm named upload.aspx. In the .aspx file, i removed all the content apart from the page directive. It’s content look like this:

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="upload.aspx.cs" Inherits="upload" %>

Then in the CodeBehind, I added the following:

using System;
using System.IO;

public partial class upload : System.Web.UI.Page
    protected void Page_Load(object sender, EventArgs e)
        // Get the data from the POST array
        string data = Request.Form["imageData"];

        // Decode the bytes from the Base64 string
        byte[] bytes = Convert.FromBase64String(data);

        // Write the jpeg to disk
        string path = Server.MapPath("~/save.jpg");
        File.WriteAllBytes(path, bytes);

        // Clear the response and send a Flash variable back to the URL Loader
        Response.ContentType = "text/plain";

There are obviously hard-coded values such as the save path but from this you should be able to create whatever system you require.