Adobe Photoshop CS5 One-on-One

3. Drag inside the image with the ruler tool. For the
   best results, we want to drag along an edge or along
   another element that ought to be exactly horizontal or
   vertical. Nothing is better for horizontal orientation
   than the actual horizon, so click under the corner of
   the building to the left of the tower and drag across
   the horizon, as shown in Figure 2-7.

As you work with the ruler tool, the options bar notes

the angle (A) and distance (D1) of the line. Angle is the

inclination of the line, which translates to the number

of degrees the line is out of plumb (off from absolute

vertical or horizontal). Distance is the length of the line.

When straightening an image, D1 is of no concern; only

A matters. And it matters only for your own curiosity

because Photoshop is going to straighten the image for

you automatically.

If you drag from left to right, as I did, the A value

will be something like –2.7 degrees. But if you drag

from right to left, the A value will be more in the

neighborhood of 177.3 degrees. Which is correct?

As it turns out, both. Which should you use to ro-

tate the image? Neither, because Photoshop will do

it for you in the next step.

4. Click the Straighten button. As soon as you draw
   a line with the ruler tool, the Straighten button in
   the options bar becomes available (see Figure 2-8).
   Click this button and watch as Photoshop magically
   aligns the photo. We still have a leaning tower, but
   the people, trees, and other buildings are properly
   upright.

Figure 2-7.

Figure 2-8.

5. Check to see what Photoshop threw away. The deceptively
   simple Straighten button actually performs two separate opera-
   tions. First, it rotates the image on the canvas (the entire image,
   including the area with no pixels) according to the angle you
   indicated with your line. Then, it crops away the empty wedges
   of canvas that are naturally created by the rotation and pares
   the image to its original shape, showing you only the finished
   product. To see what I mean, we need Photoshop to reveal what
   happened in between those two steps.

Straightening a Crooked Image 43