The combination of perspective and the characteristics of the lens you use to capture a photograph may result in any of several types of distortion in an image.
First we’ll look at keystone distortion, which occurs when an object is photographed from an angle rather than from a straight-on view. You can see keystone distortion in a picture of a tall building taken from ground level—the edges of the building appear closer to each other at the top than they do at the bottom.
- Expand the Lens Corrections panel and click Manual at the top of the panel.
- Drag the Vertical slider to the left to set a value of -80.
- Undo the last step
- In the Lens Corrections panel, drag the Distortion slider to the extreme left, and then to the right to see the effect on the image. To effectively correct the barrel distortion making the pillars in our image curve outwards, set the value to 40.
- Click the checkbox just below the five Transform sliders to activate the Constrain Crop option.
- Undo the last two steps and experiment with the other four Transform sliders, with and without the Constrain Crop option. Try combinations of settings.
Figure 1 This image is a particularly extreme example, but the adjustment we made might be acceptable if you intended to crop the shot to feature the central portal. You can see that the change has given the image a very different feel; all of the distortion sliders can be used not only to “correct” an image, but also to create effects.
This image also shows barrel distortion—a lens distortion effect that causes straight lines to bow out toward the edges of the image. The opposite of this effect is known as pincushion distortion—where straight lines bend inward.
The edges of the image are drawn inwards, leaving curved gray areas showing on all four sides. These artifacts can be cropped automatically.