Understanding Photoshop is a biweekly column that takes an in-depth look at how digital photographs are built and manipulated. It is a college-level course in plain English for free at Photofocus. To learn more see this article.
Some images will have visible distortion, which is often caused by the camera not being square with the subject. If the photographer was higher (or lower) than the image or if the photo was taken at an angle, you will see distortion. In some cases, this distortion is part of the shot composition and is desirable. In others, the distortion can be distracting. Lets square off an image:
1. Open the file Perspective.tif.
2. Select the Perspective Crop tool by clicking the Crop tool in the Tools panel and choosing the second tool in the well.
3. Crop around the window in the photo as tight as you can to frame it.
Use the pixel grid to help position the initial crop. If it is not visible, select the option Show Grid in the Options bar.
4. Drag the upper-right and upper-left corners in toward the center to line up the crop borders parallel to the edge of the window.
The crop selection will no longer look rectangular.
5. Click the Commit button or press Return (Enter). The resulting image should appear as if the angle was squared and the camera was level.
Depending on how you cropped the image, it may look slightly distorted. You can use the Image Size command with the Constrain Proportions option deselected or the Free Transform command (which you’ll learn about later in this chapter) to reshape the photo.
