Straighten an image’s horizon
When you shoot photos, environmental conditions often make it difficult to frame an image that is level in relation to the horizon—either real or virtual. In Aperture, you can straighten an image so that the horizon in the image is parallel to the bottom and top edges.
You can straighten your images using either the Straighten tool or the Straighten adjustment controls. However, you may find it most efficient to use the Straighten tool to quickly level the image and then use the Straighten controls for more precision.
Note: It’s a good idea to turn off zooming when straightening an image, so that the full image fits within the Viewer. If an image is zoomed in to its actual size, you can turn off zooming by clicking the Zoom Viewer button in the tool strip or the full-screen view toolbar (or by pressing Z).
Rotate an image using the Straighten tool
Rotating an image with the Straighten tool is as simple as selecting the tool and dragging within the image to make it straight. However, it’s important to understand that although the image appears to enlarge as you rotate it, Aperture actually crops the image so that it fits within its rectangular border without blank edges appearing on the sides.
Select a photo.
Select the Straighten tool in the tool strip or the full-screen view toolbar (or press G).
With the Straighten tool selected, drag within the image to rotate it either clockwise or counterclockwise.
As you rotate the image, a yellow grid appears to help you make the horizon perfectly straight, and the image is cropped to prevent gaps from appearing in the corners.
Rotate an image using the Straighten controls
The Straighten adjustment controls provide a high degree of precision for straightening your images.
Select a photo.
In the Adjustments inspector or the Adjustments pane of the Inspector HUD, choose Straighten from the Add Adjustment pop-up menu, and use the Angle parameter controls to straighten the image.
Increasing the value rotates the image clockwise, and decreasing the value rotates the image counterclockwise.