Image resize

Question

User-1564758913 posted

Hi, I have made a page that generates thumbnails from a larger image.

I works but the images load really slow. How can I speed this up?

 

public partial class MakeThumbnail : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            
            string file = Request.QueryString["file"];
            double dWidth, dHeight;
            int intHeight = int.Parse(Request.QueryString["maxSize"]);
            int intWidth = intHeight;  //Bilden ska passas in i en kvadrat på maxSize*maxSize pixlar

            try
            {
                System.Drawing.Image sourceImage = System.Drawing.Image.FromFile(Server.MapPath(file));

                //Räkna om antingen höjd eller bredd, utifrån proportionerna på orginalbilden

                if (sourceImage.Size.Width < sourceImage.Size.Height)
                {
                    dWidth = intWidth * (Convert.ToDouble(sourceImage.Size.Width) / Convert.ToDouble(sourceImage.Size.Height));
                    intWidth = Convert.ToInt32((Math.Round(dWidth, 0)));
                }
                else
                {
                    dHeight = intHeight * (Convert.ToDouble(sourceImage.Size.Height) / Convert.ToDouble(sourceImage.Size.Width));
                    intHeight = Convert.ToInt32((Math.Round(dHeight, 0)));
                }

                // create an image object, using the filename we just retrieved
                System.Drawing.Image image = System.Drawing.Image.FromFile(Server.MapPath(file));

                // create the actual thumbnail image
                System.Drawing.Image thumbnailImage = image.GetThumbnailImage(intWidth, intHeight, new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback), IntPtr.Zero);

                // make a memory stream to work with the image bytes
                MemoryStream imageStream = new MemoryStream();

                // put the image into the memory stream
                thumbnailImage.Save(imageStream, System.Drawing.Imaging.ImageFormat.Jpeg);

                // make byte array the same size as the image
                byte[] imageContent = new Byte[imageStream.Length];

                // rewind the memory stream
                imageStream.Position = 0;

                // load the byte array with the image
                imageStream.Read(imageContent, 0, (int)imageStream.Length);

                // return byte array to caller with image type
                Response.ContentType = "image/jpeg";
                Response.BinaryWrite(imageContent);
            }

            catch { }
        }    

        public bool ThumbnailCallback()
        {
            return true;
        }
    }

 

 

  

Answer 1

User-263151482 posted

You could use the Application/Session/Cache variable the save the thumbnails, if they are used repeatedly then only the first load takes some time and the other one's are really fast.

Answer 2

User494352855 posted

Hi, there are several reasons why your code is running slow. 

1) No caching. Image resizing is a CPU-heavy operation that will crash your site under heavy load - unless you have disk caching.

2) Your Jpegs are being saved at 100 percent quality, resulting in uneccesarily large file sizes. You can set this to 90 and get much smaller files without perceptible loss.

3) You will experience a memory leak with this code if it runs for a long time - any errors occuring during the resize will result in open/locked files and unclaimable memory. You must use the using() keyword to prevent this.

Take a look at this list of pitfalls when resizing images in ASP.NET for more details on how to do it properly..

There is also a commercial image resizer available if you'd rather use an off-the-shelf module that is well tested.