Straighten a Skewed Photo with GIMP

We’ve probably all taken pictures when the camera wasn’t perfectly aligned, resulting in a slanted horizon or a bent subject. It’s very easy to fix and straighten a skewed photo with GIMP’s rotation tool.

When you have an image with a skewed horizon, you have to lose some of the edges of the photo to fix it. The sides of the image should be cropped to compensate for the tilt of the photo due to rotation. You always need to crop a photo when you rotate it, so it makes sense to rotate and crop with the Rotate tool in one step.

Remark. GIMP 2.4.3 was used in the following tutorial. It should work for other versions up to GIMP 2.8.

Contents
  1. Submit a guide
  2. Set Rotate Tool Options
  3. Rotate image
  4. Completion of the rotation
  5. Auto crop and delete guides

Submit a guide

With your photo open in GIMP, hover over the ruler at the top of the document window. Click and drag down to hover over the image. Position the guide so that it crosses the horizon in your photo. It doesn’t have to be the actual skyline like in the practice photo here – use anything you know should be horizontal, such as a roofline or pavement.

Set Rotate Tool Options

Select the rotate tool from the tools. Set the parameters according to what we have shown here.

Rotate image

Your layer rotates as you click and drag on the image with the rotate tool. Rotate the layer so that the horizon in your photo matches the direction you placed earlier.

Completion of the rotation

The Rotate dialog box appears as soon as you move the layer. Click “Rotate” to complete the edit when you are happy with your positioning. You can then see how many ribs were lost on the turn.

Auto crop and delete guides

As a last step go to the page Image > Automatic Image Selection to remove blank edges from the canvas. Go to page Image > Guides > Delete All Guides to remove the guide.

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