It seems like the simplest thing in the world: keep the horizon straight. Even after years of shooting, the ocean still tilts and groups of penguins still list to one side. When I flop on the ground for a worm’s eye view, the odds of capturing a cock-eyed frame soar. With film these shots usually ended up in the round file, but the advent of digital and Photoshop allow me to remedy these flaws with a few clicks. Here’s how. (Most editing programs offer similar tools to the one I describe here.)

To straighten a horizon, open the offending image in Photoshop.

Use the Measure tool, located in the Eyedropper tool flyout menu.

Look for a line in the image that follows or runs parallel to the horizon. Click on one end of that line with the Measure tool and drag it to the far end. Releasing the tool leaves a highlighted line along the path.

Drag the Measure tool along the horizon line.

Finally, go to the Image menu, choose Rotate-Arbitrary. A number representing degrees from horizontal appears. Click OK. The Image automatically rotates so the horizon becomes straight. This opens black space on the canvas. Use the Crop tool to create a perfect rectangle.

Crop to cut out blank space.

While operator error is responsible for tilted horizons, the laws of optics show how wide-angle lenses tilt vertical lines toward the center of the frame when the camera points above the horizon. A shift lens or shift movement on a view camera can correct this problem when taking the picture—but for those without specialized equipment, Photoshop again comes to the rescue.

Pointing a wide-angle lens upwards makes vertical lines converge.

Until CS2, we used Free Transform to correct this kind of lens distortion. This entailed some guesswork. The new Lens Correction filter makes straightening vertical lines a snap.

Open the image. If you are comfortable with layers, created a duplicate layer and work on that. Otherwise, rename the file so you don’t irreparably harm the original. Go to the Filter menu and choose Distort. Select Lens Correction inside the Distort menu. The Lens Correction menu appears). For now ignore Chromatic Aberration and Vignetting (tools for ridding an image of color fringing and darkening at the edges of the frame. Our tool of choice is Transform. To correct vertical lines, use the Vertical slider. Before starting, make sure both the Grid and Preview boxes are checked.

The trees tilt toward the center in the picture of El Capitan in Yosemite.

The Lens Correction Menu includes a grid with several slider controls.

Moving the vertical slider to the left straightens the trees. Click OK to apply the filter.

Blank canvas intruded as the slider moved left. Click on the Crop tool to snip out a perfect rectangle. You lose some of the original image, but everything is now properly aligned. Never crop an image before applying the filter. You may need the extra space after the filter does its job.

The finished product.

Don’t only use the perspective correction feature in Lens Correction to fix tilted images, plan for it. When you see perspective problems as you shoot an image, make sure there is plenty of extra space to cut out when you crop the final image after Lens Correction—so you don’t have to cut important parts of the shot. If you have several similarly framed images, you can repeat your settings by using the Previous Conversion setting, similar to the feature of the same name in Bridge. The Horizontal slider is useful as well for correcting

	James Martin

off-center images or distortions caused by vertical corrections. Sometimes the Vertical filter bows the image horizontally, which a light application of the Horizontal slider can remedy.

To learn how to apply this powerful filter when confronted with skewed perspectives, take some distorted shot. Fooling around with tools is the best way to grasp their power and limitations.

Be sure to check out James' latest book, DIGITAL PHOTOGRAPHY OUTDOORS: A Field Guide for Adventure & Travel Photographers, published by The Mountaineers Press.

All images Copyright © James Martin