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Straightening an Image

If you're anything like me, your beautifully composed photograph will have a wonky horizon. Here's how to straighten it out accurately.

Victoria Falls at sunset [June 2001, Fuji FinePix 2300 digicam]

Photodesk is quite capable of performing rotations, but there's no preview or measurement facility and getting the right angle is just guesswork. But by switching to a different tool first you can get the information needed.

• Open the Drawing tools window, and select Line-segment outlines.
• Click on the Information icon in the toolbar (on the far left). The second section should be showing an angle icon and values labelled A and D (currently blank). The first is what we're interested in.
• Click once in your image, on a point on the horizon. The A and D icons will now show values, updating as you move the pointer around.
• Move the pointer so the line preview follows the horizon line, and take a note of the value in the A field: 1.48° here. It's best to make the line as long as possible.

  

  Finding the angle

• Press Escape to cancel the line-drawing operation (we don't actually want to draw anything).
• Now type Ctrl-R to open the Rotate image window (or select the Photodesk>Image>Rotate... menu entry).
• Select Arbitrary, and enter the negated value from the A field (ie, enter -1.48):

  

  Setting up the rotation

• If it's important to preserve your image right out to the edges, select Resize to fit, otherwise choose Lose corners, which will chop off parts falling outside the image size.
• Now click on Rotate.
• Finally, use the Crop tool to get rid of the white corners generated by the rotation. You should get something like this:

  

  The Falls, straightened

• If you get it wrong (and it can be surprisingly difficult - the example here isn't quite right, for instance), undo and start again - don't rotate the rotated image again. Every time you rotate an image you lose information, unless it's by a multiple of 90°.