Resize/Shrink Photos for Web Development

using System;
using System.Collections.Generic;
using System.IO;
using System.Web;
using System.Web.UI;
using System.Drawing.Imaging;
using System.Drawing;
using System.Drawing.Drawing2D;

namespace SilverlightApplication1.Web
{
    public partial class resize : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack) return;
            string fileName = Request["hdnFileName"];
            string strFactor = Request["hdnFactor"];
            string imgData = Request["hdnImgData"];

            string extension = ".jpg";
            string[] parts = fileName.Split(new char[] {'.'});
            if (parts.Length > 1)
            {
                extension = parts[parts.Length - 1];
            }
            ImageFormat imageFormat = ImageFormat.Jpeg;
            switch (extension)
            {
                case "jpg":
                case "jpeg":
                    imageFormat = ImageFormat.Jpeg;
                    break;
                case "png":
                    imageFormat = ImageFormat.Png;
                    break;
                case "gif":
                    imageFormat = ImageFormat.Gif;
                    break;
                case "bmp":
                    imageFormat = ImageFormat.Bmp;
                    break;
                case "tiff":
                    imageFormat = ImageFormat.Tiff;
                    break;
            }

            double factor = 0;
            if (!Double.TryParse(strFactor, out factor))
            {
                throw new ArgumentException("Invalid factor (should be of type Double)");
            }

            byte[] buffer = Convert.FromBase64String(imgData);
            Image img = null;
            using (MemoryStream stream = new MemoryStream())
            {
                stream.Write(buffer, 0, buffer.Length);
                img = Image.FromStream(stream);
            }

            int originalWidth = img.Width;
            int originalHeight = img.Height;

            int width = Convert.ToInt32(factor * originalWidth);
            int height = Convert.ToInt32(factor * originalHeight);

            // see e.g. http://www.glennjones.net/Post/799/Highqualitydynamicallyresizedimageswithnet.htm
            Bitmap newImage = new Bitmap(width, height, img.PixelFormat);
            Graphics g = Graphics.FromImage(newImage);
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
            g.PixelOffsetMode = PixelOffsetMode.HighQuality;
            g.SmoothingMode = SmoothingMode.HighQuality;
            System.Drawing.Rectangle rect = new Rectangle(0, 0, width, height);
            g.DrawImage(img, rect); 
            // newImage now contains the resized image

            using (MemoryStream ms = new MemoryStream())
            {
                newImage.Save(ms, imageFormat);
                ms.Seek(0, SeekOrigin.Begin);

                int length = (int)ms.Length;
                buffer = new byte[length];
                ms.Read(buffer, 0, length);
            }

            Response.Clear();
            Response.AddHeader("Content-Disposition", String.Format("attachment; filename={0}", fileName));
            Response.AddHeader("Content-Length", buffer.Length.ToString());
            Response.ContentType = String.Format("image/{0}", imageFormat.ToString());

            Response.BinaryWrite(buffer);
            Response.End();
        }
    }
}