Correcting perspective distortion
Perspective distortion is something you'll often find in photos that contain straight lines, such as the lines of a building. This type of distortion comes in the form of converging or diverging lines. For example, if you take a photo looking up at a tall building, the sides of the building will form converging lines, getting closer together higher up the building.
New York City, Lower Manhattan, Financial District, Broadway Av. : Equitable Building 1915 by (vincent desjardins) on flickr (licensed CC-BY)
Often this effect can be put to good use, to create an image that is more compelling than if the straight lines were perfectly vertical (or horizontal). But there are some instances where perspective distortion may be unwanted. For example, in architecture photography, perspective distortion is sometimes avoided.
There are a few different ways that perspective distortion can be removed, which I'll look at in this article. These techniques can also be reversed if you want to add or increase perspective distortion in your photos.
