Following up on an earlier post about using the Measure/Ruler tool in Photoshop, I’ve got a quick tip on how to accurately straighten an image. Let’s say you have an image of buildings, trees or other objects that are tilted in your image, or the scanned image is tilted. You want them to be straight, but making the image a layer and using the rotate tool doesn’t always produce accurate results, requiring you to undo and try again. 
The easiest way to straighten the image accurately is is to select the Measure/Ruler tool as described in the earlier post (Shift + i three times), then draw a line with the tool at the exact same angle as the building, tree or other object you wish to straighten out. Once the line is drawn, go to Image>Image Rotation>Arbitrary and take a look at the Angle field in the Rotate Canvas dialog box. You’ll notice that the angle is already set. In the sample image above, you can see that I’ve drawn the line with the Measure tool along the edge of the white box and invoked the dialog box. The white box is at an angle of 2.21. If I hit OK, the image is automatically straightened perfectly (provided the line you’ve drawn is accurate).
