Dynamic DeepZoom ASP.NET User Control using Seadragon

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.SessionState;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
using System.IO;
using System.Net;
using IWshRuntimeLibrary;
    /// <summary>
    /// Summary description for GetTileImage
    /// </summary>
public class GetTileImage : IHttpHandler, IRequiresSessionState
{
    const string c_key = "dzi";

    public void ProcessRequest(HttpContext context)
    {
        //context.Response.Cache.SetMaxAge(TimeSpan.FromMinutes(60));
        WshShell sh = new WshShell();
        
        int level = int.Parse(context.Request["level"]);
        int x = int.Parse(context.Request["x"]);
        int y = int.Parse(context.Request["y"]);
        int tileSize = int.Parse(context.Request["tileSize"]);
        int tileOverlap = int.Parse(context.Request["tileOverlap"]);
        string imageUrl = context.Request["image"];

        Bitmap source = LoadImage(imageUrl);
        if (source == null)
            return;

        Bitmap tile = CreateTileImage(source, level, x, y, tileSize, tileOverlap);

        context.Response.ContentType = "image/jpeg";
        ImageCodecInfo[] icf = ImageCodecInfo.GetImageEncoders();
        EncoderParameters encps = new EncoderParameters(1);
        encps.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 85L);
        //tile.Save(context.Response.OutputStream, icf[1], encps);
        foreach (ImageCodecInfo info in icf)
        {
            if (string.Compare(info.FormatDescription, "JPEG") == 0)
            {
                tile.Save(context.Response.OutputStream, info, encps);
                break;
            }
        }
    }

    public bool IsReusable
    {
        get
        {
            return true;
        }
    }

    Bitmap CreateTileImage(Bitmap source, int level, int x, int y, int tileSize, int tileOverlap)
    {
        int width, height;
        if (source.Width > source.Height)
        {
            width = (int)Math.Pow(2, level);
            height = width * source.Height / source.Width;
        }
        else
        {
            height = (int)Math.Pow(2, level);
            width = height * source.Width / source.Height;
        }
        tileSize = Math.Min(tileSize, (int)Math.Pow(2, level));
        int tileLeft = x * tileSize - tileOverlap;
        int tileWidth = tileSize + 2 * tileOverlap;
        int tileTop = y * tileSize - tileOverlap;
        int tileHeight = tileSize + 2 * tileOverlap;
        if (tileLeft < 0)
        {
            tileLeft += tileOverlap;
            tileWidth -= tileOverlap;
        }
        if (tileTop < 0)
        {
            tileTop += tileOverlap;
            tileHeight -= tileOverlap;
        }

        float ratio = (float)source.Width / width;
        float srcLeft = tileLeft * ratio;
        float srcWidth = tileWidth * ratio;
        float srcTop = tileTop * ratio;
        float srcHeight = tileHeight * ratio;
        if (srcLeft + srcWidth > source.Width)
        {
            srcWidth = source.Width - srcLeft;
            tileWidth = (int)Math.Round(srcWidth / ratio);
        }
        if (srcTop + srcHeight > source.Height)
        {
            srcHeight = source.Height - srcTop;
            tileHeight = (int)Math.Round(srcHeight / ratio);
        }

        Bitmap bmp = new Bitmap(tileWidth, tileHeight);
        Graphics g = Graphics.FromImage(bmp);
        g.InterpolationMode = InterpolationMode.HighQualityBicubic; 
        g.DrawImage(source,
            new RectangleF(0, 0, tileWidth, tileHeight),
            new RectangleF(srcLeft, srcTop, srcWidth, srcHeight),
            GraphicsUnit.Pixel);
        g.Dispose();
        return bmp;
    }

    public static Bitmap LoadImage(string imageUrl)
    {
        Dictionary<string, Bitmap> images = (Dictionary<string, Bitmap>)HttpContext.Current.Session[c_key];
        if (images == null)
        {
            images = new Dictionary<string, Bitmap>();
            HttpContext.Current.Session[c_key] = images;
        }
        Bitmap bmp = null;
        if (!images.ContainsKey(imageUrl))
        {
            try
            {
                string url = imageUrl;
                if (!Uri.IsWellFormedUriString(url, UriKind.Absolute))
                    url = HttpContext.Current.Server.MapPath(url);

                WebClient wc = new WebClient();
                Stream fs = wc.OpenRead(url);
                bmp = new Bitmap(fs);
                fs.Close();
            }
            catch { return null; }
        }
        else
        {
            bmp = images[imageUrl];
            images.Remove(imageUrl);
            Dictionary<string, Bitmap> tmp = new Dictionary<string, Bitmap>();
            foreach (string key in images.Keys)
                tmp.Add(key, images[key]);
            images = tmp;
            HttpContext.Current.Session[c_key] = images;
        }
        images.Add(imageUrl, bmp);
        if (images.Count > 5)
        {
            Dictionary<string, Bitmap>.KeyCollection.Enumerator e = images.Keys.GetEnumerator();
            e.MoveNext();
            string key = e.Current;
            images.Remove(key);
        }
        return bmp;
    }
}