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Hack 66 Level That Dipping Horizon

Wrangling with LCD viewfinders sometimes leads
to less than perfectly level horizon lines. Thankfully, a hidden tool
in Photoshop CS can straighten things out.

I know that my digital
camera's LCD monitor isn't the best
tool for lining up straight images. But I like that little television
screen for so many other things, such as gauging exposure in real
time, that I use it anyway. There are days, however, when composing a
picture in the LCD feels like backing up a trailer into the driveway.
I turn the steering wheel one way, and the trailer goes the other.

Even professional photographers using cameras mounted on tripods have
problems composing scenes accurately. They might think they have a
straight image, only to be unpleasantly surprised when opening the
picture on the computer to see that the horizon line is dipping
slightly to the right. Thanks to Photoshop, it's
easy to straighten those images.

Figure 6-8 shows a horizon line that needs to be
straightened. I can use the
Rotate Canvas command to guesstimate the
amount I need to adjust the photo, but it might not be accurate. And
I'll have to keep guessing and cropping until I get
the picture right. But there's a better way!

Figure 6-8. A crooked horizon doesn't have to stay that way

In Photoshop CS, there's a handy-dandy little ruler
that will help you find accurate horizontal and vertical angles.
What, you don't see it in the floating Tools
palette? That's because it's hidden
behind the Eyedropper icon. Click on the Eyedropper, hold down the
mouse button, and you'll see a Color Sampler tool
and a Measure tool. Select the Measure tool.

Using your mouse, place the tool cursor in your image window on one
end of the line you wish to straighten and then drag it across to the
other end of the line. When you release the mouse, the Measure tool
calculates the angle needed to straighten the line. Photoshop
remembers this angle.

Now, select ImageRotate CanvasArbitrary.
Photoshop automatically fills the angle measurement and direction of
rotation in the dialog box. In fact, the dialog box displays the
precise angle adjustment that is needed, as shown in Figure 6-9.

Figure 6-9. The precise correction amount, filled in for you

Click OK to straighten your image. Now, all you have to do is crop
off the crooked corners, and it's just like nothing
ever went wrong (see Figure 6-10).

Figure 6-10. The straightened image

This trick also works for straightening vertical lines, for those
times when that lamppost looks as if it's leaning to
the right or that skyscraper resembles the Leaning Tower of Pisa.
From now on, use the Measure tool to keep everything on the straight
and narrow.

Jan Blanchard