I don’t know how often one comes across something like this, but at least in UBC, this phenomenon is quite common. There are many student clubs that sell exam packages, which can be handy dandy for students preparing for exams, especially when the professors provide little or no practice problems. But these student clubs often throw in a disgusting shade of background color to prevent photocopying or scanning then printing these exam packages.
So they might look like this:
Let’s solve this bloody problem.
But before we get to playing with Photoshop, let’s say you are like me, stuck with a large single pdf file that contains dozens of pages of material. If you have several files that are not too big (eg. contains one page in each file), you can skip this section.
Dealing with pdf files too large to photoshop
If you try to work directly on a very large file in Photoshop, then I hope you have a much bigger RAM than I do. For the rest of us, we will split the large pdf file up using PDF Split and Merge. This installer version worked on my WinXP without a problem. Choose “split” on the left panel to get started.
Similar tools should be available for large files in other formats.
Ok, now you have a whole bunch of pages in separate files to work with. Open one of them in Photoshop. We will record the sequence of actions that we are going to apply to this image, in order to apply the same actions to the other files. So firstly, open Window in the menubar, then check Actions.
Now click on the Create new set icon (looks like a folder) on the bottom of the Action panel to create a new Folder. You can name it “Remove Background”. Then click on the Create new action icon, and name your new icon “Remove red background”. Finally, click on Begin recording. Now everything you do will be recorded and repeated when you run this action.
Now the real deal: Removing the bloody background.
First: Image -> Adjustments -> Desaturate.
Your image should look like this:
Then: Image -> Adjustments -> Brightness/Contrast…
Here you have to play with the number a bit to get the best result. You might also want to magnify your image first, to see the quality of the text better.
You can stop recording the action by clicking on the Stop playing/recording icon in the Actions panel. Then this is pretty important: Close this file without saving. This is because we would apply the same actions (desaturate, brightness & contrast) to every file, including the one we just worked on.
Batch process the images
File -> Automate -> Batch…
For Source, choose Folder and select the folder where you stored the images with ugly background.
For Destination, also choose Folder, but create a new folder to store the cleaned up images.
Then OK it, and watch Photoshop do all the work in front of your eyes! (I attempted to take a video capture for this, but Batch processing combined with video capture proved to be too much for my old laptop)
Now you can run PDF Split & Merge again to merge them into one pdf file.
Disclaimer: I do not encourage pirating the PhotoshopCS2 program nor using this tutorial to make copies of the exam package without the copyright holders’ consent. Why this tutorial you ask? Well, I’m sure the rightful buyers of the exam packages would want to remove the bloody background for their eyes 🙂