This GIMP (GNU) tutorial explains how to straighten a crooked horizon using the Rotate Tool. To work along, you are welcome to download the Start Image I am working with Here. Unzip the file and open the image onto GIMP’s workspace.
You can quickly Undo a step at any time by pressing Ctrl then Z. Alternatively, click a previous Undo History snapshot - Windows then Dockable Dialogues then click Undo History. In addition, to Zoom in (or Zoom out) of your image; from the top menu choose View then select a Zoom Tool from the subsequent drop-down list.
The Crop And Rotate Tools
Launch GIMP & Organise Its Workspace & Palettes
Open your choice of Start Image onto GIMP’s workspace - File then Open - Ctrl then O.
Duplicate Your Image
It’s important to preserve your original image: therefore, Duplicate your image; Ctrl then D - (Image then Duplicate). Now, close the original image, and work on the Duplicated image.
Ensure the Layers and the Undo History Palettes are visible, and then drag them into position over your workspace - (Windows then Dockable Dialogues - then click Layers and Undo History).
Now, from the left-side Toolbox, activate the Rotate Tool.
Then left-click once over your photograph, and you will see the following Rotate dialogue box.
Hover your cursor over your image’s far right-side, or far left-side, (over the beige workspace), until you see the following Rotate Icon.
Then left-click. Now, moving your cursor in a semicircular movement, swivel your image upwards or downwards - until the horizon looks reasonably straight - as illustrated below.
And when you are satisfied that the horizon looks reasonably straight, click the Rotate tab to commit the rotation.
You may need to repeat the Rotate process until you have successfully straightened the horizon.
Congratulations, you have straightened your image’s horizon, and you are now ready for the next step.
3/ Utilise The Crop Tool
To finish, from the left-side Toolbox, activate the Crop Tool.
Then, leaving out the transparent edges that where unavoidably caused by the Image Rotation, left-click and drag out a Crop Bounding Box, ensuring it incorporates just your image - as illustrated below.
Then left-click once over your image to commit the Crop.
Congratulations, you have successfully straightened your image’s horizon, and your work is ready to save.
Wendi E. M. Scarth. Top of Page.