The GetThumbnailImage method of the Bitmap class in GDI+ and C# is used to create a small thumbnail image of a lange image. The following code snippet/page shows how to create an image thumbnail using Bitmap.GetThumbnailImage method.

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.IO;
using System.Text;
using System.Net.Mail;
using System.Text.RegularExpressions;
using System.Threading;

public partial class _Default : System.Web.UI.Page
{   
    private string Finalimagename = "";   
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void btnUpload1_Click(object sender, EventArgs e)
    {
        ImageUpload();
    }

     private void ImageUpload()
   {      
        /* this code used to make directory name RealImage */       
        Directory.CreateDirectory(Server.MapPath("RealImage\\"));      
        HtmlInputFile htmlFile = (HtmlInputFile)BrowseImage0;
        if (htmlFile.PostedFile.ContentLength > 0)
        {
            string sFormat = String.Format("{0:#.##}", (float)htmlFile.PostedFile.ContentLength / 2048);
            if (float.Parse(sFormat) < float.Parse("2048"))
            {
                if (htmlFile.PostedFile != null)
                {
                    ViewState["ImageName"] = htmlFile.PostedFile.FileName.Substring(htmlFile.PostedFile.FileName.LastIndexOf("\\") + 1);//browseImagePath[0];                   
                }
                else
                {
                    ViewState["ImageName"] = "";
                }
            }
            else
            {
                lblError1.Visible = true;
                lblError1.Text = "Image Size is Large, please resize it !!";               
            }
        }
        else
        {
            ViewState["ImageName"] = "";
            if (ViewState["ImageName"].ToString() == "")
            {
                lblError1.Visible = true;
                lblError1.Text = "Attach an image to upload";
            }
            return;
        }

        //This function is used to make image thumbnail
        MakeThumbnail();
    }

    //Return thumbnail callback
    public bool ThumbnailCallback()
    {
        return true;
    }
    //For image thumbnial
    private void MakeThumbnail()
    {
        System.Drawing.Image myThumbnail150;
        object obj = new object();
        obj = BrowseImage0;
        System.Drawing.Image.GetThumbnailImageAbort myCallback = new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback);
        HtmlInputFile hFile = (HtmlInputFile)obj;
        if (hFile.PostedFile != null && hFile.PostedFile.ContentLength > 0)
        {
            //this code used to remove some symbols between image name and replace with space
            string imgname1 = hFile.PostedFile.FileName.Replace('%', ' ').Substring(hFile.PostedFile.FileName.LastIndexOf("\\") + 1);
            string imgname2 = imgname1.Replace('#', ' ').Substring(imgname1.LastIndexOf("\\") + 1);
            string imgname3 = imgname2.Replace('@', ' ').Substring(imgname1.LastIndexOf("\\") + 1);
            string imgname4 = imgname3.Replace(',', ' ').Substring(imgname1.LastIndexOf("\\") + 1);
            string imgname5 = imgname4.Replace('&', ' ').Substring(imgname1.LastIndexOf("\\") + 1);
           
            Finalimagename = imgname5.ToString();
 
            string imgname = hFile.PostedFile.FileName.Substring(hFile.PostedFile.FileName.LastIndexOf("\\") + 1);
            string sExtension = imgname.Substring(imgname.LastIndexOf(".") + 1);
 
            //this code is used to check image extension
            if (sExtension.ToLower() == "jpg" || sExtension.ToLower() == "gif" || sExtension.ToLower() == "bmp" || sExtension.ToLower() == "jpeg")
            {
                if (!File.Exists(MapPath("RealImage\\" + Finalimagename)))
                {
                    hFile.PostedFile.SaveAs(ResolveUrl(Server.MapPath("RealImage\\" + Finalimagename)));
 
                    System.Drawing.Image imagesize = System.Drawing.Image.FromFile(ResolveUrl(Server.MapPath("RealImage\\" + Finalimagename)));
                    Bitmap bitmapNew = new Bitmap(imagesize);
                    if (imagesize.Width < imagesize.Height)
                    {
                         myThumbnail150 = bitmapNew.GetThumbnailImage(150 * imagesize.Width / imagesize.Height, 150, myCallback, IntPtr.Zero);
                    }
                    else
                    {
                        myThumbnail150 = bitmapNew.GetThumbnailImage(150, imagesize.Height * 150 / imagesize.Width, myCallback, IntPtr.Zero);
                    }
                   
                        //Create a new directory name ThumbnailImage
                        Directory.CreateDirectory(Server.MapPath("ThumbnailImage"));
                        //Save image in TumbnailImage folder
myThumbnail150.Save(ResolveUrl(Server.MapPath("ThumbnailImage\\")) + Finalimagename,
System.Drawing.Imaging.ImageFormat.Jpeg);
                        MessageLabel.Text = "Successfully uploaded"
                }
            }
            else
            {
                lblError1.Visible = true;
                lblError1.Text = "Check image extension";
            }
        }
    }
}

Output :

First of all upload image.



Figure1.

This is real image.



Figure2.

This is thumbnail image.



Figure3.

For more information download attached file.