ASP.NET上传后处理缩略图的最佳方法

Question

I've read about creating a HttpHandler to call each time I want to show a thumbnail where it will perfom the resizing for me. I've also heard about some other solutions, but I was wondering which solution would be the best for a social networking website where thumbnails are shown all over the place on each page and everywhere.

Would it be good to resize and save the image on the disk after the origianl file has been uploaded? What's the best way to reference these images?

Does anyone have any advice for me? Thank you.

Answer 1

Would it be good to resize and save the image on the disk after the origianl file has been uploaded? What's the best way to reference these images?

Definitely, that's what Twitter does, for example, and most websites when thumbnails need to be displayed. This is time consuming. You don't want your user to sit idle while you do this on every image every time.

Store the thumbnails on disk and keep a reference to the thumbnails on the database. Or store them on the db itself. I don't want to get into that debate about disk vs DB but just don't resize them every time. It should be done ONCE.

Answer 2

Here is some resize Code if you need it, the first you set a max height and width and it created a thumbnail with the same aspect retio as the original that do now violate either max.

The second, if you know the actual size of the final image and don't need to worry about aspect ratios is fatr simpler.

    public Image Thumbnail(Image FullsizeImage, int MaxHeight, int MaxWidth)
    {

        try
        {
            // This has to be here or for some reason this resize code will
            // resize an internal Thumbnail and wil stretch it instead of shrinking
            // the fullsized image and give horrible results
            FullsizeImage.RotateFlip(System.Drawing.RotateFlipType.Rotate180FlipNone);
            FullsizeImage.RotateFlip(System.Drawing.RotateFlipType.Rotate180FlipNone);


            System.Drawing.Image NewImage;


            if (!((MaxWidth < FullsizeImage.Width) || (MaxHeight < FullsizeImage.Height)))
                NewImage = FullsizeImage;
            else
            {
                float HeightRatio = 1;
                float WidthRatio = 1;
                HeightRatio = (float)FullsizeImage.Width / FullsizeImage.Height;
                WidthRatio = (float)FullsizeImage.Height / FullsizeImage.Width;


                float DrawHeight = (float)FullsizeImage.Height;
                float DrawWidth = (float)FullsizeImage.Width;

                if (MaxHeight < FullsizeImage.Height)
                {
                    DrawHeight = (float)MaxHeight;
                    DrawWidth = MaxHeight * HeightRatio;
                }
                if (MaxWidth < DrawWidth)
                {
                    DrawWidth = MaxWidth;
                    DrawHeight = DrawWidth * WidthRatio;
                }

                NewImage = FullsizeImage.GetThumbnailImage((int)(DrawWidth),
                       (int)(DrawHeight), null, IntPtr.Zero);
            }

            return NewImage;

            // To return a byte array for saving in a db 
            //ms = new MemoryStream();

            //NewImage.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);

            //NewImage.Dispose();
            //FullsizeImage.Dispose();

            //return ms.ToArray();
        }
        catch
        {
            return null;
        }
        finally
        {

        }
    }

    public Image Resize(Image OrigImage, int NewHeight, int NewWidth)
    {
        if (OrigImage != null)
        {                
            Bitmap bmp = new Bitmap(OrigImage, new Size(NewWidth, NewHeight));
            bmp.SetResolution(this.ImageResolution, this.ImageResolution);
            Graphics g = Graphics.FromImage(bmp);
            return bmp;
        }
        else
        {
            return null;
        }
    }