Fixing a photographic distortion in GIMP

Posted on April 11, 2010

The scene: You’ve taken a photo of your latest masterpiece, you’re quite sure the camera was square on with the painting but, having had a look at the photo, you weren’t square on. The camera never lies!

But it’s OK, we’ll fix it in GIMP.

Here’s the photo I’m starting with:

As you can see, the width of the top of the painting is shorter than the width at the bottom, so the top of the painting is actually tilted away from the camera.

First thing I do is to crop the image, removing anything we don’t need. This is done using the crop tool:

You simply draw a box with the painting inside it. Don’t worry about being to specific on first go as you can alter the size of the box by dragging the corners/sides of the box to fine tune it. With the box in place, click inside the box and you’ll trim off the outsides. I’m left with:

Next we click the perspective tool:

And click on the painting. This will now let us distort the painting to bring it back to being square. Four squares will appear, one in each corner. These are the four places where you can grab and distort the image:

What I usually do is try and line up the sides of the painting with the sides of the viewing area, as the horizontal and vertical sides of the view area are definitely right. You can see below that the top right corner is good, but the top left is out, so I need to fix that, and the two bottom corners.

With all corners in place I click OK in the perspective window that popped up when I first clicked the perspective tool. That’s me, I’m done!

Do NOT try and stretch UP a photo. By that, I mean don’t try and use the perspective tool to make a small photo larger, as you’ll just blur it as the computer tries to fill in details that were never there. ALWAYS work on the largest, most detailed photo you have, save it, then if need be scale it down and save it again. ALWAYS keep your large images safe.

All that’s left now is if I wanted to do colour correction or sharpening of the image. If you do, check my other tutorial on colour correction which is HERE.

Is there anything you don’t know how to do with your photos in software and would like explained? Drop me an email/comment and if I can help, I’ll make a GIMP tutorial on it.