I recently completed a project that required a thumbnail image automatically be generated from the first page of every PDF file that is uploaded to the system. I was rather surprised to find that there was no drop in solution for such a thing. There are many libraries out there that can create a PDF file from HTML content or an image, but no standalone libraries that could go from PDF to an image. After testing out a couple of methods, I was able to find what I believe to be the easiest and least invasive method to implement it in a web application..
What You Will Need
To generate images from PDF in your project, you will need a couple of things.
Ghostscript, a set of libraries for working with a PDF. You will need to download the version specific to your environment (32 bit/64 bit). You can download those here.
GhostscriptSharp, a wrapper for using the Ghostscript libraries in .NET. You can download it here. It is written in C#, so if you are using VB.NET you will need to create a code sub-directory in your Web.config to use the file in your project.
You will need to do a couple of things to get the Ghostscript components to function before you write any code. First, you need to extract the gsdll file to a location on your system. (Either gsdll32.dll or gsdll64.dll depending on your CPU.)
Then, you need to modify GhostscriptSharp.cs to specify the path to the Ghostscript library that you extracted before. Look for this code on line 12 of the GhostscriptSharp.cs file:
#region Hooks into Ghostscript DLL [DllImport("gsdll64.dll", EntryPoint = "gsapi_new_instance")] private static extern int CreateAPIInstance(out IntPtr pinstance, IntPtr caller_handle); [DllImport("gsdll64.dll", EntryPoint = "gsapi_init_with_args")] private static extern int InitAPI(IntPtr instance, int argc, string argv); [DllImport("gsdll64.dll", EntryPoint = "gsapi_exit")] private static extern int ExitAPI(IntPtr instance); [DllImport("gsdll64.dll", EntryPoint = "gsapi_delete_instance")] private static extern void DeleteAPIInstance(IntPtr instance); #endregion
You will need to change the paths in the DllImport constructors to the location of the file on your machine. The DllImportAttribute only accepts a constant string, so you cannot pass a variable with the path or using a Web.config value. This prevents you from using Server.MapPath to generate the path to your project’s bin folder, which is also unfortunate.
The actual implementation of the image generation from PDF is very simple once you have reached this point. You just need to make a call to the GhostscriptWrapper.GeneratePageThumb method with the path to the PDF, and the path where the image should be saved. You also specify the page number you want to generate from and the height and width of the final image. A call to GeneratePageThumb might look like this:
// Creates a 100 x 100 thumbnail of page 1. GhostscriptWrapper.GeneratePageThumb(pdfFileName, outputFileName, 1, 100, 100);
You will also need to import the GhostscriptSharp namespace in your code file. That is all that there is to it! After running your application, you will see the image file in the specified path.
Its important to note that GeneratePageThumb is a shortcut method that will only generate a JPG image. If you need to have more control over the output of your image, then you will need to use the GenerateOutput method and pass in a GhostscriptSettings object that contains all of your required values. The GhostscriptSharp link above provides more detailed examples if you need them.
Thanks for reading! If you have any troubles with the process, feel free to leave a comment below.