What is the “best” way to create a thumbnail using ASP.NET? [closed]

Question

Story: The user uploads an image that will be added to a photo gallery. As part of the upload process, we need to A) store the image on the web server's hard drive and B) store a thumbnail of the image on the web server's hard drive.

"Best" here is defined as

• Relatively easy to implement, understand, and maintain
• Results in a thumbnail of reasonable quality

Performance and high-quality thumbnails are secondary.

Answer 1

I suppose your best solution would be using the GetThumbnailImage from the .NET Image class.

// Example in C#, should be quite alike in ASP.NET
// Assuming filename as the uploaded file
using ( Image bigImage = new Bitmap( filename ) )
{
   // Algorithm simplified for purpose of example.
   int height = bigImage.Height / 10;
   int width = bigImage.Width / 10;

   // Now create a thumbnail
   using ( Image smallImage = image.GetThumbnailImage( width, 
                                                       height,
                                                       new Image.GetThumbnailImageAbort(Abort), IntPtr.Zero) )
   {
      smallImage.Save("thumbnail.jpg", ImageFormat.Jpeg);
   }
}

Answer 2

GetThumbnailImage would work, but if you want a little better quality you can specify your image options for the BitMap class and save your loaded image into there. Here is some sample code:

Image photo; // your uploaded image

Bitmap bmp = new Bitmap(resizeToWidth, resizeToHeight);
graphic = Graphics.FromImage(bmp);
graphic.InterpolationMode = InterpolationMode.HighQualityBicubic;
graphic.SmoothingMode = SmoothingMode.HighQuality;
graphic.PixelOffsetMode = PixelOffsetMode.HighQuality;
graphic.CompositingQuality = CompositingQuality.HighQuality;
graphic.DrawImage(photo, 0, 0, resizeToWidth, resizeToHeight);
imageToSave = bmp;

This provides better quality than GetImageThumbnail would out of the box

Answer 3

Using an example above and some from a couple of other places, here is an easy function to just drop in (thanks to Nathanael Jones and others here).

using System.Drawing;
using System.Drawing.Drawing2D;
using System.IO;

public static void ResizeImage(string FileNameInput, string FileNameOutput, double ResizeHeight, double ResizeWidth, ImageFormat OutputFormat)
{
    using (System.Drawing.Image photo = new Bitmap(FileNameInput))
    {
        double aspectRatio = (double)photo.Width / photo.Height;
        double boxRatio = ResizeWidth / ResizeHeight;
        double scaleFactor = 0;

        if (photo.Width < ResizeWidth && photo.Height < ResizeHeight)
        {
            // keep the image the same size since it is already smaller than our max width/height
            scaleFactor = 1.0;
        }
        else
        {
            if (boxRatio > aspectRatio)
                scaleFactor = ResizeHeight / photo.Height;
            else
                scaleFactor = ResizeWidth / photo.Width;
        }

        int newWidth = (int)(photo.Width * scaleFactor);
        int newHeight = (int)(photo.Height * scaleFactor);

        using (Bitmap bmp = new Bitmap(newWidth, newHeight))
        {
            using (Graphics g = Graphics.FromImage(bmp))
            {
                g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                g.SmoothingMode = SmoothingMode.HighQuality;
                g.CompositingQuality = CompositingQuality.HighQuality;
                g.PixelOffsetMode = PixelOffsetMode.HighQuality;

                g.DrawImage(photo, 0, 0, newWidth, newHeight);

                if (ImageFormat.Png.Equals(OutputFormat))
                {
                    bmp.Save(FileNameOutput, OutputFormat);
                }
                else if (ImageFormat.Jpeg.Equals(OutputFormat))
                {
                    ImageCodecInfo[] info = ImageCodecInfo.GetImageEncoders();
                    EncoderParameters encoderParameters;
                    using (encoderParameters = new System.Drawing.Imaging.EncoderParameters(1))
                    {
                        // use jpeg info[1] and set quality to 90
                        encoderParameters.Param[0] = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 90L);
                        bmp.Save(FileNameOutput, info[1], encoderParameters);
                    }
                }
            }
        }
    }
}

Answer 4

Here is an extension method in VB.NET for the Image Class

Imports System.Runtime.CompilerServices

Namespace Extensions
   ''' <summary>
   ''' Extensions for the Image class.
   ''' </summary>
   ''' <remarks>Several usefull extensions for the image class.</remarks>
   Public Module ImageExtensions

      ''' <summary>
      ''' Extends the image class so that it is easier to get a thumbnail from an image
      ''' </summary>
      ''' <param name="Input">Th image that is inputted, not really a parameter</param>
      ''' <param name="MaximumSize">The maximumsize the thumbnail must be if keepaspectratio is set to true then the highest number of width or height is used and the other is calculated accordingly. </param>
      ''' <param name="KeepAspectRatio">If set false width and height will be the same else the highest number of width or height is used and the other is calculated accordingly.</param>
      ''' <returns>A thumbnail as image.</returns>
      ''' <remarks>
      ''' <example>Can be used as such. 
      ''' <code>
      ''' Dim _NewImage as Image 
      ''' Dim _Graphics As Graphics
      ''' _Image = New Bitmap(100, 100)
      ''' _Graphics = Graphics.FromImage(_Image)
      ''' _Graphics.FillRectangle(Brushes.Blue, New Rectangle(0, 0, 100, 100))
      ''' _Graphics.DrawLine(Pens.Black, 10, 0, 10, 100)
      ''' Assert.IsNotNull(_Image)
      ''' _NewImage = _Image.ToThumbnail(10)
      ''' </code>
      ''' </example>
      ''' </remarks>
      <Extension()> _
      Public Function ToThumbnail(ByVal Input As Image, ByVal MaximumSize As Integer, Optional ByVal KeepAspectRatio As Boolean = True) As Image
         Dim ReturnImage As Image
         Dim _Callback As Image.GetThumbnailImageAbort = Nothing
         Dim _OriginalHeight As Double
         Dim _OriginalWidth As Double
         Dim _NewHeight As Double
         Dim _NewWidth As Double
         Dim _NormalImage As Image
         Dim _Graphics As Graphics

         _NormalImage = New Bitmap(Input.Width, Input.Height)
         _Graphics = Graphics.FromImage(_NormalImage)
         _Graphics.DrawImage(Input, 0, 0, Input.Width, Input.Height)
         _OriginalHeight = _NormalImage.Height
         _OriginalWidth = _NormalImage.Width
         If KeepAspectRatio = True Then
            If _OriginalHeight > _OriginalWidth Then
               If _OriginalHeight > MaximumSize Then
                  _NewHeight = MaximumSize
                  _NewWidth = _OriginalWidth / _OriginalHeight * MaximumSize
               Else
                  _NewHeight = _OriginalHeight
                  _NewWidth = _OriginalWidth
               End If
            Else
               If _OriginalWidth > MaximumSize Then
                  _NewWidth = MaximumSize
                  _NewHeight = _OriginalHeight / _OriginalWidth * MaximumSize
               Else
                  _NewHeight = _OriginalHeight
                  _NewWidth = _OriginalWidth
               End If
            End If
         Else
            _NewHeight = MaximumSize
            _NewWidth = MaximumSize
         End If
         ReturnImage = _
            _NormalImage.GetThumbnailImage(Convert.ToInt32(_NewWidth), Convert.ToInt32(_NewHeight), _Callback, _
                                    IntPtr.Zero)
         _NormalImage.Dispose()
         _NormalImage = Nothing
         _Graphics.Dispose()
         _Graphics = Nothing
         _Callback = Nothing
         Return ReturnImage
      End Function
   End Module
End Namespace

Sorry the code tag doesn't like vb.net code.

Answer 5

You can use the Image.GetThumbnailImage function to do it for you.

http://msdn.microsoft.com/en-us/library/system.drawing.image.getthumbnailimage.aspx (.NET 3.5)

http://msdn.microsoft.com/en-us/library/system.drawing.image.getthumbnailimage(VS.80).aspx (.NET 2.0)

public bool ThumbnailCallback()
{
  return false;
}

public void Example_GetThumb(PaintEventArgs e)
{
  Image.GetThumbnailImageAbort myCallback = new Image.GetThumbnailImageAbort(ThumbnailCallback);
  Bitmap myBitmap = new Bitmap("Climber.jpg");
  Image myThumbnail = myBitmap.GetThumbnailImage(40, 40, myCallback, IntPtr.Zero);
  e.Graphics.DrawImage(myThumbnail, 150, 75);
}

Answer 6

Avoid GetThumbnailImage - it will provide very unpredictable results, since it tries to use the embedded JPEG thumbnail if available - even if the embedded thumbnail is entirely the wrong size. DrawImage() is a much better solution.

Wrap your bitmap in a using{} clause - you don't want leaked handles floating around...

Also, you'll want to set your Jpeg encoding quality to 90, which is where GDI+ seems to shine the best:

System.Drawing.Imaging.ImageCodecInfo[] info = System.Drawing.Imaging.ImageCodecInfo.GetImageEncoders();
System.Drawing.Imaging.EncoderParameters encoderParameters;
encoderParameters = new System.Drawing.Imaging.EncoderParameters(1);
encoderParameters.Param[0] = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 90L);

thumb.Save(ms, info[1], encoderParameters);