You've taken what you thought was the perfect photo, only to discover that the lens on your camera has distorted the image in some way. Objects appear to be bending or bowing. The perspective is skewed. Or maybe the corners are dark. Whatever the situation, the Photoshop Lens Correction filter may be able to help.
As its name implies, the Lens Correction filter makes minor alterations to your photos in order to fix problems caused by the limitations of your camera's lens. Issues such as blurriness, improper focus, or a thumb blocking half the picture are not covered. However, perspective issues caused by poor camera angle are.
Lens correction was available in previous versions of Photoshop, but with CS5, Adobe added auto-correction capabilities that use actual data from your camera's lens to correct most minor problems quickly and effortlessly, without any real human intervention. (Yes, the machines are getting smarter; be afraid.)
The Lens Correction filter works with 8-bit and 16-bit RGB and grayscale images only. Raw images or those with metadata work best. To get started select Filter > Lens Correction. Photoshop will display a status bar and update its database of lens profiles.
Adobe provides built-in profiles for a wide assortment of cameras and lenses that make it easier to get very precise and accurate filtering results. Dropdowns are available for camera make, camera model, and lens information.
If your particular camera or lens is missing, don't worry. An online search tool allows you to find additional cameras and lenses not included with the software. If you prefer to create your own profile, you can do that, too. Just enter your camera's specs into the online profile creator tool. Profiles obtained or created in this manner can then be added to the list for future reference.
The filter's auto-correction features include geometric distortion, chromatic aberration, and vignette (that darkening of the corners mentioned above). Unfortunately, "subtract 10 pounds" and "make 10 years younger" are not options (yet). Checkboxes make it easy to choose the settings appropriate for you. An Auto Scale Image option tells Photoshop what to do in case changes will affect the photo's canvas size. Choices include filling additional space with a white, black, or transparent background, or enlarging the image to fill the space.
Custom correction settings are also available, in case you want to fine-tune your results.
Nobody's perfect - and neither is your camera lens. The Lens Correction filter helps to counteract some of these imperfections.