When used with its Straighten option, the Ruler tool squares off a crooked image based on a line you drag and also crops the image to remove any blank canvas areas that result around its borders.
To straighten a crooked image:
- Choose the Ruler tool (I or Shift-I).
- Drag along a feature in the image that you want to orient horizontally or vertically.A If you need to adjust the line, move either endpoint. The current angle is listed as the A value on the Options bar.
- On the Options bar, click Straighten.B Easy!
- To straighten an image without cropping it, hold down Alt/Option as you click Straighten and until the command is done processing.