Straightening Buildings, Part 1: The Crop Tool

The Crop tool offers Photoshop users a quick and dirty method for correcting a building photo’s perspective and effectively “straightening” the structure

This article is the first of two that deals with the subject of straightening buildings. Have you ever taken a photograph of a building or some other subject with a rectangular or square construction (such as a building) only to find the subject tilted and in a low-angle perspective because you’re on the ground and it’s a few stories tall? This quick tutorial will show how the Crop tool of all things can make quick work of a common perspective problem.

Figure 1: The original image: Salisbury House in Des Moines.

Figure 1 is a photo of Salisbury House in Des Moines, Iowa—an English manor house built here in the 1920s. I like the photo but because of the topography I shot at a low angle and so the building has a distinct perspective. Here’s how to straighten things up with the Crop Tool:

Step 1: Select the Crop Tool (C) and drag for your desired crop area, as usual. If your image is already cropped as much as you want it, just drag a crop region that encompasses the full image.

Step 2: Note that when you have a crop region selected, the Crop Tool’s options in the Options bar change (see Figure 2). The Perspective checkbox is most likely unchecked; check it.

Figure 2: The Crop Tool’s options.

Figure 3: My crop selection, with verticals aligned to the building.

Step 3: With the Perspective checkbox checked, you can now drag each anchor point of the crop selection. Drag the handles so the selection’s horizontals are where they were but the verticals match the perspective angle of the subject or building. Look at Figure 3 and note the crop selection takes up the full space except on the sides, where the verticals are slanted (the area outside the crop selection is darkened to help illustrate this). To match the verticals to the building’s perspective, I like to temporarily place the crop selection so its left edge lies along the left edge of the building and then drag the anchor points to match it. Figure 4 shows how I’ve done this for the right edge, matching its angle with the right edge of the building. Don’t do this with a part of the building closer to the center, since the angles nearer the center will naturally be more vertical.

Figure 4: A detail of my crop selection, aligned right on top of the right edge of the building.

Step 4: Once your crop selection’s verticals match the perspective of the building, press Return/Enter to commit the crop. The building will distort to conform to the new crop perspective and instantly straighten. Figure 5 shows how Salisbury House fared. Note that fixing perspective can make the image look stretched either horizontally or vertically; use the Free Transform command and stretch the image so it looks correct.

Figure 5: After the fix, Salisbury House stands straight up—not at an angle.

If you want to take the technique a step further, align the horizontals with the building as well as the verticals. This puts the crop selection in full perspective and not only straightens the building but makes it seem the camera was shooting straight-on. Figures 6 and 7 shows my crop selection and the final image respectively.

Figure 6: The crop selection, with all four sides aligned with the building.

Figure 7: The building is now aligned with the image edges on all four sides.

On Friday, April 14 I will publish Part 2 of the Straightening Buildings series, which will focus on the Perspective and Distort commands (under Edit –> Transform). I like to these commands together to crop and straighten product shots of picture frames, which often come in with a perspective that makes the frames look warped and not square. With Perspective and Distort it’s pretty easy to fix.