Now, I am going to tell you how to Re-size Image along with maintain the ration employing ASP.NET 4.5.2 and C# code. Sometimes we must store totally different size images to get a certain images as applied to e-commerce web page. for that we both re-size the image and save multiple images collectively small, medium along with a full size image. Other then When we've got issue relating to space having very fine performance server then we are able to use dynamically re-sizing of image merely save only huge image then when want to utilize re-size it in run time when you need.

For achieving this process I generate a code that response the re-size image. I utilize it for jpg and png images not for gif. Call the page in which code for image merging :
Image1.ImageUrl = "dynamicimage.aspx";

And this is the Code for image generation and merging (dynamicimage.aspx or dynamicimage.aspx.cs) using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.IO;
protected void Page_Load(object sender, EventArgs e)
{
  string testimage = Server.MapPath(@"images/hemant_image.jpg");
  getimage(testimage, 400, 400); 
  // can set imageurl, max-width and max-height using query string...
}
public void getimage(string ThumbnailPath, int maxwidth, int maxheight)
{
    System.Drawing.Image image = System.Drawing.Image.FromFile(ThumbnailPath);
    Size ThumbNailSize = setimagesize(maxwidth, maxheight, image.Width, image.Height);
    System.Drawing.Image ImgThnail = new Bitmap(ThumbNailSize.Width, ThumbNailSize.Height);
    System.Drawing.Graphics graphics = System.Drawing.Graphics.FromImage(ImgThnail);  
    graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
    graphics.SmoothingMode = SmoothingMode.HighQuality;
    graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;
    graphics.CompositingQuality = CompositingQuality.HighQuality;
    graphics.DrawImage(image, 0, 0, ThumbNailSize.Width, ThumbNailSize.Height);
    ImageCodecInfo[] info = ImageCodecInfo.GetImageEncoders();
    EncoderParameters encoderParameters;
    encoderParameters = new EncoderParameters(1);
    encoderParameters.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 100L);
    string sExt = System.IO.Path.GetExtension(ThumbnailPath);
    if (sExt.ToString() == ".png")  
  {
        Response.ContentType = "image/png";
        ImgThnail.Save(Response.OutputStream, image.RawFormat);
    }
    else
    {
        Response.ContentType = "image/jpeg";
        ImgThnail.Save(Response.OutputStream, info[1], encoderParameters);
    }
    image.Dispose();
}
// below code is my old one for calculating height and width with maintain image ratio.
public Size setimagesize(int maxwidth, int maxheight, int OriginalWidth, int OriginalHeight)
{
    Size NewSize = new Size();
    int sNewWidth = OriginalWidth;
    int sNewHeight = OriginalHeight;
    int tempheight = 0;
    int tempwidht = 0;
    if (OriginalWidth >= OriginalHeight)
    {
        if (OriginalWidth >= maxwidth)
        {
            sNewWidth = maxwidth;
            sNewHeight = OriginalHeight * maxwidth / OriginalWidth;
        }
        if (sNewHeight > maxheight)
        {
            tempheight = sNewHeight;
            sNewHeight = maxheight;
            sNewWidth = sNewWidth * maxheight / tempheight;
        }
    }
    else
    {
        if (OriginalHeight >= maxheight)
        {
            sNewHeight = maxheight;
            sNewWidth = OriginalWidth * maxheight / OriginalHeight;        }
        if (sNewWidth > maxwidth)
        {
            tempwidht = sNewWidth;
            sNewWidth = maxwidth;
            sNewHeight = sNewHeight * maxwidth / tempwidht;
        }
    }
    NewSize = new Size(sNewWidth, sNewHeight);
    return NewSize;
}