Creating Website Thumbnails in ASP.NET


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Creating a small thumbnail image of a website can be a useful task. This is particularly the case with sites that are directories of websites. A thumbnail helps give the user some idea about the content of a site that they might click to visit.

Although there are a couple of gotchas, doing this from ASP.NET is fairly straight forward. The process involves creating a WebBrowser control to load and render the website image, and write that image to a bitmap.

Using the WebBrowser Control to Create a Thumbnail

The WebBrowser control is an ActiveX control. Normally, you create one of these by placing it on a Windows Form. Here, we’ll just create one dynamically without any form. One problem is that this control can only be created in a single-threaded apartment. This is the tricky part of this code. We need to create a new thread, set its apartment state to single-threaded apartment, and then run it. This worker thread will create the control and generate the thumbnail. Listing 1 shows my code for the WebsiteThumbnail class.

Listing 1. WebsiteThumbnail Class

using System;
using System.Drawing;
using System.Threading;
using System.Web;
using System.Windows.Forms;

public class WebsiteThumbnail
  protected string _url;
  protected int _width, _height;
  protected int _thumbWidth, _thumbHeight;
  protected Bitmap _bmp;

  /// <summary>
  /// Generates a website thumbnail for the given URL
  /// </summary>
  /// <param name="url">Address of website from which to generate the
  /// thumbnail</param>
  /// <param name="width">Browser width</param>
  /// <param name="height">Browser height</param>
  /// <param name="thumbWidth">Width of generated thumbnail</param>
  /// <param name="thumbHeight">Height of generated thumbnail</param>
  /// <returns></returns>
  public static Bitmap GetThumbnail(string url, int width, int height,
    int thumbWidth, int thumbHeight)
    WebsiteThumbnail thumbnail = new WebsiteThumbnail(url, width, height,
      thumbWidth, thumbHeight);
    return thumbnail.GetThumbnail();

  /// <summary>
  /// Protected constructor
  /// </summary>
  protected WebsiteThumbnail(string url, int width, int height,
    int thumbWidth, int thumbHeight)
    _url = url;
    _width = width;
    _height = height;
    _thumbWidth = thumbWidth;
    _thumbHeight = thumbHeight;

  /// <summary>
  /// Returns a thumbnail for the current member values
  /// </summary>
  /// <returns>Thumbnail bitmap</returns>
  protected Bitmap GetThumbnail()
    // WebBrowser is an ActiveX control that must be run in a
    // single-threaded apartment so create a thread to create the
    // control and generate the thumbnail
    Thread thread = new Thread(new ThreadStart(GetThumbnailWorker));
    return _bmp.GetThumbnailImage(_thumbWidth, _thumbHeight,
      null, IntPtr.Zero) as Bitmap;

  /// <summary>
  /// Creates a WebBrowser control to generate the thumbnail image
  /// Must be called from a single-threaded apartment
  /// </summary>
  protected void GetThumbnailWorker()
    using (WebBrowser browser = new WebBrowser())
      browser.ClientSize = new Size(_width, _height);
      browser.ScrollBarsEnabled = false;
      browser.ScriptErrorsSuppressed = true;

      // Wait for control to load page
      while (browser.ReadyState != WebBrowserReadyState.Complete)

      // Render browser content to bitmap
      _bmp = new Bitmap(_width, _height);
      browser.DrawToBitmap(_bmp, new Rectangle(0, 0,
        _width, _height));

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