Generating an Image of a PDF Page

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.

Setup

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 Code

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.

Fixing reCAPTCHA.net 404 Errors

Last week, Google decommissioned the reCAPTCHA API components that were hosted on recaptcha.net.  According to reCAPTCHA support, the change was supposed to have occurred back in April, but for some reason or another the site has only now been replaced with a 404 error.

The good news is that Google has not made any changes to the reCAPTCHA API, so you will just need to change the reCAPTCHA path from the old location to the new location hosted with Google.

In your application, all instances of this URL:

http://api.recaptcha.net

need to be replaced with this:

http://www.google.com/recaptcha/api

You will need to change all references to that URL, including the recaptcha.js or recaptcha_ajax.js files and the /verify URL.  It is as simple as that.  Keep in mind that if your site uses SSL then you need to change the “http” in the URL to “https”.

Many Joomla users have been affected by this problem as well.  Luckily a proposed fix has already been committed to Joomla’s GitHub repository.  To view those changes or to download the updated file, click here.  If you’re not confident enough to fix the issue on your own, a formal patch should be on it’s way from Joomla soon.

Feel free to leave a comment if you have any questions.  Thanks for reading!

Iterating Over an Enumerable – Creating a “Days of the Week” Drop Down Menu

Enumerations are extremely valuable for managing sets of numeric values such as status codes or days of the week.  Most of the time, you would create an enumerable to simplify values used in multiple points that have the same representation, in order to improve the readability and re-usability of your code.  However, there are some situations where using the enumeration’s name and value directly on the presentation layer can make sense.

For example, let’s say we have a form where we need the user needs to choose a day of the week to assign to a particular record.  We can easily generate a drop down list of values using the built in DayOfWeek enum that is included by default in the System library.

Code

Let’s create a Drop Down List on our page.  We will generate the list items in code behind, so we will just leave those blank.  It should look something like this:

<br />&lt;asp:DropDownList ID="ddlDay" runat="server"&gt;&lt;/asp:DropDownList&gt;<br />

In our code behind file, we will use a couple of helpers from the System.Enum namespace to allow us to loop through our enumerable's values and get their names for use in the list item.  Here's the code for our page load event:

<br />Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load<br /><%%KEEPWHITESPACE%%>    If Not Page.IsPostBack() Then<br /><%%KEEPWHITESPACE%%>        ' Get the values of the DayOfWeek Enum (0-6).<br /><%%KEEPWHITESPACE%%>        Dim daysOfTheWeek = System.Enum.GetValues(GetType(DayOfWeek))<br /><br /><%%KEEPWHITESPACE%%>        For Each value In daysOfTheWeek<br /><%%KEEPWHITESPACE%%>            ' Get the name that corresponds to each value.<br /><%%KEEPWHITESPACE%%>            Dim name = System.Enum.GetName(GetType(DayOfWeek), value)<br /><br /><%%KEEPWHITESPACE%%>            ' Add a new list item, using our name and value.<br /><%%KEEPWHITESPACE%%>            ddlDay.Items.Add(New ListItem(name, value))<br /><%%KEEPWHITESPACE%%>        Next<br /><%%KEEPWHITESPACE%%>    End If<br />End Sub<br />

It's that simple.  Now you know that the value that gets posted back to the server will match directly with the values defined in the enumeration, even if the values were to change at a later date.

A Caveat

One thing to keep in mind are that this is only a user friendly option for single word names.  For example, if you have a value that represents a process' status that is named "InProgress", it would appear as a single word in the drop down as well.  You could parse the name to add the space, but there are cases where that could over complicate the process.

Thanks for reading!