Dynamically resizing an image

It's being displayed on the web form. What is actually happening is the browser is translating the binary from the image field in my database into the gif, the actual image isn't on the web form itself.

           private System.Drawing.Image GetImage(int _id) {
                                                //get image from your database etc
                  return ret;
            }

            private int ReadVal(string name, int def) {
                  int ret = def;
                  if(Request.QueryString[name] != null) {
                        try {
                              ret = System.Convert.ToInt32(Request.QueryString[name]);
                        }
                        catch {}
                  }
                  return ret;
            }

            public bool ThumbnailCallback() {
                  return false;
            }

            private void Page_Load(object sender, System.EventArgs e) {
                  float x,y,newx,newy,deltax,deltay;
                  float scale;
                  int force;
                  if(Request.QueryString["id"] == null) {
                        throw new System.Exception("must have id") ;
                  }
                  System.Drawing.Image img = GetImage(System.Convert.ToInt32(Request.QueryString["id"]));
                  x = ReadVal("x", img.Size.Width);      
                  y = ReadVal("y", img.Size.Height);
                  force=ReadVal("force", 0);

                  newx = img.Size.Width;
                  newy = img.Size.Height;
                  if(img.Size.Width > x || img.Size.Height > y || force == 1) {
                        deltax = img.Size.Width - x;
                        deltay = img.Size.Height - y;
                        scale = deltax > deltay ? x / newx : y / newy;
                        newx = newx * scale;
                        newy = newy * scale;
                  }

                  if(newx != img.Size.Width) {
                        System.Drawing.Image.GetThumbnailImageAbort myCallback = new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback);
                        img = img.GetThumbnailImage((int) newx,(int) newy,myCallback,IntPtr.Zero);
                  }
                  Response.ContentType = "image/jpeg" ;
                  img.Save(Response.OutputStream, ImageFormat.Jpeg);
            }


You will notice that this example is using GetThumbnailImage() ... this can cause problems if the images you are dealing with have embedded thumbnails

for example ...

I have an 800x600 image that I want to resize to 400x300 ...
if I use GetThumbNailImage() and this image has a thumbnail image it will blow up the thumbnail image to 400x300 as opposed to shrinking the 800x600 to 400x300 ... this can cause alot of loss in your image or some funnier results in images due to the thumbnail not being the same as the original image!


The following code does not have this problem but can execute slower in some circumstances.

             public System.Drawing.Image ResizeImage(System.Drawing.Image poImage, System.Drawing.Size poSize) {

 

                     //Detach image from its source

                     System.Drawing.Image oImageOriginal = (System.Drawing.Image)poImage.Clone();

 

                     //Resize new image

                     System.Drawing.Image oResizedImage = new System.Drawing.Bitmap(poSize.Width, poSize.Height, oImageOriginal.PixelFormat);

                     System.Drawing.Graphics oGraphic =  Graphics.FromImage(oResizedImage);

                     oGraphic.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality ;

                     oGraphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality ;

                     oGraphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic ;

                     Rectangle oRectangle = new Rectangle(0, 0, poSize.Width, poSize.Height);

                     oGraphic.DrawImage(oImageOriginal, oRectangle);

                     oGraphic.Dispose() ;

                     oImageOriginal.Dispose();

                     return oResizedImage;

              }

 


Cheers,

Greg

I think I understand,  but what is the "ret" variable in the:

   private System.Drawing.Image GetImage(int _id) {
                                                //get image from your database etc
               return ret;

Is ret an int or image?

image ...

 private System.Drawing.Image

its a placeholder for your own routine.

Greg

I tried setting ret as:

System.Drawing.Image ret = new System.Drawing.Image();, and set it to read my binary from the DB but it said cannot convert image to binary....

do I have to do a conversion from binary to image...?

yes.


mine is ...

            private System.Drawing.Image GetImage(int _id) {
                  MyDataLayer.Files File;
                  System.Drawing.Image ret = null;
                  MemoryStream str;
                  if(Request.QueryString.Count > 0) {
                        File = MyDataLayer.Files.GetById(_id) ;
                        str = new MemoryStream(File.FileData);
                        ret = System.Drawing.Image.FromStream(str);
                  }
                  return ret;
            }


File Data on my object is a byte [] which I then put a memorystream around and tell the image object to parse.

Greg

What is "MyDataLayer.Files File;"?  When I put it in my code I get :

The type or namespace name 'MyDataLayer' could not be found (are you missing a using directive or an assembly reference?)

its my data layer which returns a file from my database ... you should replace that code with your own.

Greg