Erase your friends for fun and profit

About a year ago, at SIGGRAPH 2007, researchers Shai Avidan and Ariel Shamir presented a paper on content-aware image resizing--a method for resizing (and removing objects from) images without distorting them too much.

In a nutshell, the software identifies low-information seams within an image, and cuts out (or multiplies) those seams in order to decrease or increase the image's size without changing too drastically the meat of the image.

Avidan and Shamir produced an explanatory video on the technique, which I've embedded below. If you haven't yet seen this video, I recommend you check it out.

After I saw this video, I wished that my image editing program of choice, the Gimp, could be made to perform this trick. Fortunately, it wasn't long before a content-aware resizing plugin for the Gimp appeared, complete with support for identifying parts of an image to discard.

The plugin, called Liquid Rescale, is easy (and free) to acquire, and it's pretty straightforward to use, as well. Here's how to do it.

Step One: Bring out the Gimp

GIMP, which stands for GNU Image Manipulation Program, is an open source application that's similar in function to Photoshop. I use the Gimp for all of my image manipulation needs.

• If you're a Windows user, you can get the Gimp here.
• If you're a Linux user, your computer probably came preinstalled with the Gimp.
• If you're a Mac user, you can get the Gimp from a couple of different places, but if you're going to use the Liquid Rescale plugin, you'll have to follow the not-for-beginners directions here.
   

 Step Two: Get the Plugin

• For Windows users, the plugin lives here.
• For Linux users, the plugin is available here. I use Ubuntu 8.04, and I installed the plugin packages that had been built for the previous Ubuntu version, and they worked fine. Liquid Rescale is actually available straight from Ubuntu's software repositories, but in an older, slower version, so stick with packages l've cited here.
• For Mac users, follow the instructions in the link above. (again, sadly, they involve some software compilation--not the end of the world, but by no means noob-friendly.
   

 Step Three: Use the Plugin

• Fire up the Gimp, and open an image you'd like to manipulate. I'm looking to erase this friendly-looking dog from the waters of Ocean Beach.
• Next, open the Liquid Rescale plugin dialog at "Layer," "Liquid Rescale."
• In the section of the dialog labeled "Feature discard mask," hit the "New" button. This will create a new layer to define the part of your image you'd like to do away with.
• Use the Gimp's pencil tool to color the part of the image you wish to discard red. I've found that drawing a border around the part of the image, and then using the paint can tool to fill it in works pretty well.
• Back at the Liquid rescale dialog, hit the "Refresh" button to refresh your layer, and then click the "Autosize" button to have the software reduce the image enough to erase the bit you're cutting out.
• Next, hit "OK" and let the plugin work its magic.
   

I've found that the Liquid Rescale plugin usually works fairly well, but results vary from image to image. In this beach image example, the lines of surf on either side of the dog I've cut out don't quite match up, and there's a visible seam where the dog had been. I found that a bit of judicious smudging helped matters. Also, I've found that in order to completely excise certain parts of an image, I've had to fiddle with the "Strength" slider.