Straighten a Crooked Horizon in Pixelmator - Simple Digital Photo Correction

Straighten a Crooked Picture in Pixelmator

This is a really simple fix to straighten a crooked horizon in Pixelmator. Crooked horizons are a common problem affecting digital photos, particularly those quickly grabbed snaps that we take with our compact cameras. A landscape that appears to be sliding out of the side of the frame can really undermine an otherwise attractive photo. Fortunately, if you use Pixelmator, the popular and competitively priced image editor for Apple Macs running OS X, it is very easy to straighten a horizon in any of your digital photos that are afflicted by this complaint.

If you use an Apple Mac but aren't familiar with Pixelmator, you may want to read our introduction to Pixelmator to find out if it may be a suitable image editor for you.

If you already have a copy of Pixelmator installed on your Apple Mac, the following tutorial will show you just how easy it is to straighten a crooked horizon in Pixelmator. Even if you're a completely new user of Pixelmator or image editors in general, you should have no trouble following this tutorial and you will be introduced to Pixelmator's guides, transformation and crop tools.

Open an Image with a Crooked Horizon

Obviously, the first thing you'll need to follow this tutorial is a photo with a crooked horizon which is in need of straightening. I cheated and took a straight photo and rotated it a little, effectively carrying out the opposite of what we're going to achieve in this tutorial.

Go to File > Open and navigate to the crooked photo that you want to straighten and click on it to select it before pressing the Open button.

Place a Guide

Now you've opened your photo, the first step is to place a guide to help us judge when we have successfully managed to straighten the horizon.

If you cannot see any rulers at the top and left of the Pixelmator window, go to View > Show Rulers or press the Cmd and R keys on your keyboard simultaneously. The rulers can help to make accurate placements of objects in a document, especially when zoomed in close, but one of their most useful features is that they allow you to drag guides onto your images. These guides are cyan-colored horizontal and vertical lines that are quite separate from your image. If you print an image with guides applied to it, the guides will not be visible and you can hide the guides at any point by going to View > Hide Guides.

To place a horizontal guide on your image, click on the top ruler and, while holding the mouse button down, drag downwards. You'll see a cyan line follow your cursor down the page. Drag the guide down to the horizon and place it so that it intersects the horizon approximately at the mid-point.

In the next step, we'll rotate the photo, using this guide to judge when we have straightened the horizon.

Rotate the Photo to Straighten the Horizon

The transformation tools in Pixelmator make it very easy to straighten a horizon and I'll show you how now.

Go to Edit > Transform or press the Cmd and F keys simultaneously to display the Transform bar. You'll also note that a bounding box has been placed around the photo with grab handles at each corner and one on each side.

You have two options for rotating the photo and it will be a matter of personal choice which you prefer to use. The first option is to place your cursor outside of the bounding box (the cursor will change to a right-angle with double headed arrows) and then click and drag to rotate the image. As you do so, you will see the value in the Angle field in the Transform bar changes to reflect the amount of rotation.

Your second option is to change the angle by clicking the arrows next to the Angle field or typing a new value directly into the Angle box. Sometimes this can make it easier to make a very specific rotation.

There is in fact a third option also, but not one that offers any great practicality. To the left of the Angle field is a small circle icon with a dot inside it. The dot is actually a grab handle and you can click and drag that to rotate the image, but it is difficult to achieve any degree of accuracy through this method.

However you choose to rotate the image, your goal is the same, to attempt to align the horizon with the guide that you placed previously. Once the horizon aligns with the guide, you can be sure that you have managed to straighten the horizon accurately and you can either double-click inside the bounding box or press the OK button on the Transform bar to commit your rotation.

You now have an image with a straight horizon, but the rotation has left some ugly spaces around the borders of the image. Next we'll use the crop tool to remove these areas.

Crop the Image

The rotated image may now have a straight horizon, but it also has spaces around the edges. The easiest way to remove these spaces is to crop the image. Obviously this will reduce the size of the final image, but if maintaining the original dimensions is important and you have a degree of skill with the Clone Stamp tool, you could paint these areas in to match the adjacent areas. That is, however, a more advanced exercise and we're going to go the cropping route.

Select the Crop tool from the Tools palette. Now, with the cursor placed above and to the left of the top left hand corner of the image click and drag down until the cursor is below and to the right of the bottom right hand corner of the image. Then release your mouse button and you'll see that a new bounding box has been placed over the image, again with grab handles at the corners and on the sides. 

The inside of the box has two vertical and two horizontal guides that divide the space into thirds and are designed to make it easier to judge a balanced composition. As we're just going to crop away the edges of the photo, we won't make any use of these guides.

Now click on the top left hand grab handle and, holding down the Shift key, drag it inwards and downwards a little. By holding the Shift key as you do this, the proportions of the crop box are constrained, meaning that our cropped image will have the exact same proportions as the original. Don't use the Shift key if you want to crop the image to a different format.

When happy with the position of the top left corner, grab the bottom right handle and drag that inwards and upwards. Feel free to adjust the positioning of these handles until the boundary of the cropping box is entirely within the borders of the photo. When the cropping box is placed correctly, just hit the Return key on your keyboard to crop the image.

The above couple of paragraphs assume that you rotated your image in a clockwise direction like me. If you rotated your photo in an anti-clockwise direction, you wll need to adjust the top right and bottom left grab handles of the cropping box.

If you now go to View > Hide Guides, the guide will be hidden and you can clearly see your newly corrected photo with its straightened horizon.