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The Big Fixx: digital-camera image probl... > Repairing Keystoning Without the Cro...

Repairing Keystoning Without the Crop Tool

Keystoning is often found in photos with buildings or tall objects, where the buildings look as if they’re falling away from the viewer (giving the impression that the tops- of these buildings are narrower than their bases). The Crop tool has a Perspective function that can fix these distortions, but actually I’m going to recommend that you don’t use it, because it doesn’t offer a preview of any kind—you’re just guessing, so use this technique instead.

Step One.
Open an image that has a keystoning problem (such as the photo shown here, taken with a wide-angle lens, where the building seems to be leaning away from the viewer).

Step Two.
Grab the bottom-right corner of your image window and drag outward to reveal the gray canvas background. Press Command-A (PC: Control-A) to Select All and then press Command-T (PC: Control-T) to bring up the Free Transform function. Grab the center point of the bounding box and drag it straight downward until it touches the bottom-center Free Transform point (as shown here at the cursor location near the bottom of the photo).

Step Three.
Press Command-R (PC: Control-R) to make Photoshop’s rulers visible. Click-and-drag a guide out from the left ruler into your photo (we’ll use this straight guide to help us line up our building). In the example shown at left, I lined up the guide with the edge of the bottom balcony on the front (beach side) of the building. Once you add this guide, you can really see how far back the building was leaning, and why a keystoning repair is so necessary.

Step Four.
Once your guide is in place, hold the Command key (PC: Control key) and adjust the top-left and right-corner points of the bounding box until the corners of the balconies align with your guide. Making this correction can sometimes make your building look a bit “smushed” and “squatty” (my official technical terms), so you can release the Command/Control key, grab the top-center point, and drag upward to stretch the photo back out and fix the “squattyness” (again, technically speaking).

Step Five.
When the photo looks right, press Return (PC: Enter) to lock in your transformation. (Note: By repairing this problem with Free Transform, you got to see an onscreen preview of what you were doing, which the Crop tool’s Perspective feature doesn’t offer.) Now you can drag your guide back to the rulers, and hide the rulers again by pressing Command-R (PC: Control-R). There’s still one more thing you’ll probably have to do to complete this repair job.

Step Six.
If, after making this adjustment, the building looks “round” and “bloated,” you can repair that problem by going under the Filter menu, under Distort, and choosing Pinch. Drag the Amount slider to 0%, and then slowly drag it to the right (increasing the amount of Pinch), while looking at the preview in the filter dialog, until you see the roundness and bloating go- away. (In the example shown here, I used 5% for my Amount setting.) When it looks right, click OK to complete your keystoning repair. A before and after are shown on the following page.

In the original photo, the building appears to be “falling away.”

The same photo after repairing the perspective distortion (known as keystoning).

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