Correcting Perspective Distortion with GIMP

The GNU Image Manipulation Program, also known as GIMP, is free software used to edit, retouch, and manipulate images.

Content
  1. Save the practice file
  2. Post your recommendations
  3. Set perspective tool options
  4. Activate Perspective Tool
  5. Adjust the angles to level the building
  6. Auto crop and delete guides

Save the practice file

You probably have photos of tall buildings in your collection. You may have noticed that the sides appear to be tilted at the top due to the perspective from which the photo was taken. We can fix this with GIMP’s perspective tool.

If you want to continue, you can right click on the image here and save it to your computer. Then open the image in GIMP and go to the next page. We’ll be using GIMP 2.4.3 for this tutorial. You may need to adapt these instructions for other versions.

Post your recommendations

With the photo open in GIMP, hover over the ruler on the left side of the document window. Click and drag to place the guide on the image. Position the guide so that it is close to one of the slanted sides of the object you want to straighten in the photo.

Then drag a second guide for the other side of the building.

If you think you need horizontal adjustment, drag a few horizontal guides and move them closer to the roofline or any other part of the image you know should be horizontal.

Set perspective tool options

Activate the Perspective Tool from the GIMP Tools. Set the following options:

  • Direction: Normal (Forward)

  • Interpolation: Sink (Lanczos3)

  • Clipping: clip to result

  • Sample image

  • Number of grid lines: 15

Activate Perspective Tool

Click once on the image to activate the tool. The Perspective dialog box appears and you see squares in each of the four corners of your image.

Adjust the angles to level the building

The image may look a bit strange after you fix it. The building often looks distorted in the opposite direction, even if the walls are now vertically aligned. This is because your brain expects some perspective distortion when you look at a tall building. Guru and graphic artist Dave Hass offers this advice: “I always leave a bit of original distortion to keep the image natural for the viewer.”

Move the perspective dialog to the side if it blocks your image, then drag the bottom corners of the image out of the way so that the sides of the building align with the vertical guides you placed earlier. Leaves a small amount of original distortion as you adjust the sides.

You only need to compensate a little bit to make the corrected photo look more natural. Move the corners up or down if you need to adjust the horizontal alignment.

You can always click Reset in the Perspective dialog box if you want to start over.

Otherwise click transform in the perspective dialog box to complete the edit when you are satisfied with the setting.

Auto crop and delete guides

The sloping sides of the building should now look much straighter.

As a last step, go to the page Image crop image to remove blank edges from the canvas.

Go to page Image Guides Delete all guides to remove the guide.

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