Straighten a Crooked Photo with GIMP

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Save the Practice File

Crooked Photo
Save the practice image. © Sue Chastain

We've probably all taken pictures when the camera wasn't perfectly level, resulting in a skewed horizon line or a crooked object. It's very easy to correct and straighten a crooked photo using the rotate tool in GIMP.

Whenever you have an image with a skewed horizon, you must lose something from the edges of the photo to fix it. The sides of the image must be cropped to make up for the slanting of the photo from rotation. You always have to crop a photo when you rotate, so it makes sense to rotate and crop in one step with the rotate tool.

Feel free to save the practice image here, then open it in GIMP so you can follow along. I'm using GIMP 2.4.3 for this tutorial. It should work for other versions up to GIMP 2.8 as well. 

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Place a Guideline

Place a Guideline
© Sue Chastain

With the photo open in GIMP, move your cursor to the ruler at the top of the document window. Click and drag down to put a guideline on the image. Place the guideline so it intersects with the horizon in your photo. This doesn't necessarily have to be the actual horizon line as it is here in the practice photo – use anything that you know should be horizontal, such as a roofline or a sidewalk.

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Set Rotate Tool Options

Set Rotate Tool Options
© Sue Chastain

Select the rotate tool from the tools. Set its options to match what I've shown here.

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Rotate the Image

Rotate the Image
© Sue Chastain

Your layer will rotate when you click and drag in the image with the rotate tool. Rotate the layer so the horizon in your photo lines up with the guideline you placed earlier.

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Finalize the Rotation

Finalize the Rotation
© Sue Chastain

The rotate dialog will appear as soon as you move the layer. Click "Rotate" to complete the operation when you're satisfied with your positioning. You'll be able to see how much of the edges were lost due to the rotation after you do this. 

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Autocrop and Remove Guides

Autocrop and Remove Guides
© Sue Chastain

As a last step, go to Image > Autocrop Image to remove the empty borders from the canvas. Go to Image > Guides > Remove all Guides to remove the guideline.