View Window - Transform | Rotate to Line...                    O

 

 

Use this menu selection to rotate an image to a selected reference line. After selecting this option, left click and drag the mouse cursor  to draw the intended rotation reference line on the view window. After placing the rotation line on the view window, simply press the [Enter] key to rotate the image.

 

When rotating to a line less than or equal to 45°, the rotation line will be translated to a horizontal line.

 

When rotating to a line greater than 45°, the rotation line will be translated to a vertictal line.

 

After rotating the image, you may want to crop off the rotated image's corners by selecting the crop area and the using Transform | Crop to Selection from the view window menu.