Correcting Distortion
Of Architecture In The Computer
Text And Photography By William Sawalich
Photographers know that wide-angle lenses sometimes cause distortion.
Straight lines appear curved, especially if they’re close to
the edges of the frame. Sometimes, the effect is desirable, and other
times, it’s not.
Distortion actually can occur with
any lens. One of the most common examples is photographing architecture.
Standing at the base of a tall building with the camera pointed upward,
the lines of the building, which are actually parallel, appear to
converge in the viewfinder. This perspective distortion, called “keystoning,”
is only remedied by keeping the film plane parallel to the subject
plane, but that often means you won’t get the whole building
in the shot. Architectural photographers frequently use large-format
view cameras because their specialized movements allow the photographer
to correct problems like keystoning while they shoot.
Those optical corrections are helpful, but they’re impossible
to achieve without the right equipment. That means point-and-shoot
cameras, 35mm SLRs and even high-end medium-format cameras aren’t
readily able to deliver these corrections.
That’s where computer software can help. Armed with any camera
and almost any photo-editing program, photographers can correct architectural
distortion in the computer. All you need to do is stretch and pull
your pictures until those lines are parallel.
Correcting Perspective. In
this photograph of a downtown street, the buildings would look better—more
natural and probably more pleasing to the eye—if they weren’t
bending so dramatically toward the center of the frame. Here’s
how to correct it.
1. Open the photo with any software that allows you to work
in Layers, or at least one that will allow skewing the image.
Select the image, copy it and paste it onto a new layer. Hint: Use
your software’s ruler guides to give you a target for alignment.
2. Using the Transform function (Photoshop: Edit>Transform>Perspective),
grab the image with corner markers and stretch the top of the photo
horizontally. Using the Perspective tool, you can distort
the image equally on both sides, but this doesn’t always provide
a symmetrical result. Instead, go to Edit>Transform>Distort
and drag the corners of the image independently.
3. You’ll notice that parts of the original picture
that were once in the upper corners are now lost outside the frame.
If you absolutely have to have those details in the photo, you’ll
need to live with less correction. If you plan for this before you
shoot the image, you can leave extra space around the subject to be
cropped out later.
4. After dragging bits of your picture around, it might look
as if it has been squished. In order to remedy this, use
the same Distort tool to stretch the image taller.
5. Finally, you should see a nicely re-tooled version of your
once distorted image. Compare the before and after versions
by toggling the layer view on and off. When you’re satisfied,
merge the layers to create a finished photo, and save it with a new
file name so you can go back to the original, if desired.
