Tuesday, August 2, 2011
Fix Wide-Angle Distortion
These powerful Photoshop distortion fixes are easy, too
Distortion is a bummer. When using wide-angle lenses, it's a big bummer because it can skew a scene in very unnatural, unwanted ways. Lines that were in reality straight and parallel may now look curved and converging. So how do you fight wide-angle distortion? The best way is to combat it while you're shooting by using a high-quality rectilinear lens and keeping the camera as parallel to lines being photographed as possible. Distortion gets worse as you get closer to your subject, so maintaining a little distance can be helpful, too. But even when you use these shooting tips to minimize wide-angle distortion, it can still rear its ugly head. So here's how you go about fixing distortion in post once you get your shots into the computer.
If you're using Photoshop, you could start with Edit > Transform and use Distort, Skew and other Transform tools to reshape your image and eliminate converging lines at the edges of the frame. But this won't work for the most insidious kind of distortion, which is called barrel distortion. This type of distortion is cylindrical and causes the images to appear to curve out from the center of the frame. To correct this distortion, you need to work a little harder.
Open the image in Photoshop, and duplicate the image onto a new layer (CTRL + J), then under the Filters menu choose Distort > Spherize. You'll see your image open into a new preview window where it probably looks extra-distorted—like it has been mapped onto a globe. By default, the Spherize filter is maxed out at 100% and has made the image look perfectly round. You can drag the slider into negative values, however, and this will make that sphere appear convex. This is a great and simple way to eliminate barrel distortion from photos.
But this still isn't the most powerful wide-angle distortion repair option that Photoshop offers. For that, turn to the Lens Correction filter. Photoshop's Lens Correction capability is found under the Filters menu. It launches a separate window in which the photo will load and presents you with two primary choices: auto correction or custom. Auto correction is certainly worth a try, as it's easy enough to implement with a click. But to really get in and fine-tune barrel distortion—along with other distortions such as chromatic aberration and vignetting—you'll want to choose the custom option.
Once in the Custom panel, before you go any further, look to the checkboxes at the bottom of the screen, and be sure "Show Grid" is selected. This will provide a perfect reference for the lines you're straightening with the filter.
The top slider in the Custom control panel is for repairing geometric distortion, and you'll notice that this slider looks familiar—it works exactly the same way as the Spherize filter does, where negative values create a concave look and positive values create a convex shape in your photos. But that's not all the Lens Correction filter can do.
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