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PHOTOSHOP GURU
Fix architectural distortion easily with the Lens Correction Filter
By Jack Davis
Many photographers travel the world in search of architectural beauty. Whether they're the ancient churches of Europe or the modern skyscrapers in New York City and Chicago, some of the most photographed buildings in the world pose a unique challenge for many photographers. And, unless you're shooting the Leaning Tower of Pisa, the subjects of your images are, more often than not, meant to stand straight and undistorted.
In photos, the vertical walls of buildings often converge at the top due to the tilt of the camera at exposure, resulting in unwanted distortions. Now, with the magic of Photoshop, your images can appear as straight and undistorted as you imagined when you took the picture.
One of the latest features of Photoshop CS is the new Lens Correction Filter, which can fix most lens distortion and perspective issues, including barrel and pincushion distortion. A new set of perspective tools easily makes architectural distortions a thing of the past.
In addition to the architectural example shown in this column, the Lens Correction Filter can also quickly and effectively correct chromatic aberration, vignetting and other perspective problems with an easy-to-use interface, which includes a live preview and alignment grid.
To begin, you'll first want to increase the size of your canvas. When manipulating an image with the Lens Correction Filter, you'll need extra room to stretch the image. Let's start with the extra canvas space shown in Figure A, and select the Lens Correction filter from the Filter->Distort submenu.
FIGURE A
 
Select the Lens Correction filter from the Filter->Distort submenu. Roll over picture for a larger image.
First, as shown in Figure B, notice there is a grid in the Lens Correction filter box. This allows you to determine the straightness of your original image.
FIGURE B
 
The grid helps you see how straight your picture is before you start. Roll over picture for a larger image.
Next, rotate the image so that the subject is vertical. To correct the perspective, use the Vertical perspective slider shown in Figure C until the image looks straight or good to you. The adjustable grid provides constant visual feedback, so you can easily tell when the horizontal and vertical surfaces in your shot are lined up properly.
FIGURE C
 
Use the Transform sliders to get your surfaces lined up properly. Roll over picture for a larger image.
Next, do a little experimenting with the Remove distortion slider, sometimes also called pin cushion, to correct the optical distortion of the image.
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