Generate Thumbnails and Multiple Sizes to Disk

While the ImageResizer shines at on-the-fly image processing, you can also use it to drastically simplify pre-processing and ahead-of-time resizing as well. We strongly recommend using the dynamic method instead of pre-generating your images, as pre-generating versions reduces agility and flexibility. In the examples below, only one line is required to perform all the image decoding, format conversion, processing, resizing, and re-encoding. The rest is path/filename logic. Two different solutions are presented - 1 for processing images as they are uploaded, and another for processing images that are already saved to disk.

During Upload

This method generates 3 versions of an image as it is uploaded, adding a _thumb, _medium, and _large suffix to each filename. Uploaded files are named using a generated GUID, as uploaded file names are never safe for use as-is. Even with proper sanitization (alphanumeric filtering AND length limiting), you will encounter duplicates using uploaded filenames on your server.

  Dictionary<string, string> versions = new Dictionary<string, string>();
  //Define the versions to generate
  versions.Add("_thumb", "width=100&height=100&crop=auto&format=jpg"); //Crop to square thumbnail
  versions.Add("_medium", "maxwidth=400&maxheight=400&format=jpg"); //Fit inside 400x400 area, jpeg
  versions.Add("_large", "maxwidth=1900&maxheight=1900&format=jpg"); //Fit inside 1900x1200 area

  //Loop through each uploaded file
  foreach (string fileKey in HttpContext.Current.Request.Files.Keys) {
      HttpPostedFile file = HttpContext.Current.Request.Files[fileKey];
      if (file.ContentLength <= 0) continue; //Skip unused file controls.

      //Get the physical path for the uploads folder and make sure it exists
      string uploadFolder = MapPath("~/uploads");
      if (!Directory.Exists(uploadFolder)) Directory.CreateDirectory(uploadFolder);

      //Generate each version
      foreach (string suffix in versions.Keys) {
          //Generate a filename (GUIDs are best).
          string fileName = Path.Combine(uploadFolder, System.Guid.NewGuid().ToString() + suffix);

          //Let the image builder add the correct extension based on the output file type
          fileName = ImageBuilder.Current.Build(file, fileName, new ResizeSettings(versions[suffix]), false, true);
      }

  }

After Upload

This example method generates 3 versions of the specified file, and returns a list of the final path names.

For example,

  GenerateVersions("~/images/image.jpg")

Will generate

/images/image\_thumb.jpg
/images/image\_medium.jpg
/images/image\_large.jpg

And will return a list of those paths.

  public IList<string> GenerateVersions(string original) {
      Dictionary<string, string> versions = new Dictionary<string, string>();
      //Define the versions to generate and their filename suffixes.
      versions.Add("_thumb", "width=100&height=100&crop=auto&format=jpg"); //Crop to square 
      versions.Add("_medium", "maxwidth=400&maxheight=400format=jpg"); //Fit inside 400x400
      versions.Add("_large", "maxwidth=1900&maxheight=1900&format=jpg"); //Fit inside 1900x1200


      string basePath = ImageResizer.Util.PathUtils.RemoveExtension(original);

      //To store the list of generated paths
      List<string> generatedFiles = new List<string>();

      //Generate each version
      foreach (string suffix in versions.Keys)
          //Let the image builder add the correct extension based on the output file type
          generatedFiles.Add(ImageBuilder.Current.Build(original, basePath + suffix, 
            new ResizeSettings(versions[suffix]), false, true));

      return generatedFiles;   
  }