Correcting Skew Tutorial Author - Man1c M0g (http://forums.biorust.com/member.php?s=&action=getinfo&userid=1)

Digital cameras may have advanced greatly over the last few years, but the underlying fallibilities of photographic positioning are still as relevant as ever, and even the most professional photographer cannot keep their viewfinder perfectly level all the time. There is, however, no need to despair - Photoshop is loaded with tools that can help correct skewed horizons in mere moments.  This tutorial describes probably the simplest and most effective method for skew correction, using the often forgotten Measure Tool.

 

Step 1: Open up a stock image in Photoshop of any size and/or format. The best results for this tutorial usually involve large images with a definitive horizon or absolutely straight edge (such as the brickwork of a building, if you wish to correct the skew in an image of a building, etc). Note: Please remember that this method is only as effective as the underlying image.  If you have a source that's skewed in three dimensions, this two dimensional technique may not yield the exact results that you desire.

Step 2: Select the Measure Tool from the tools palette.  If you are having trouble finding it, its underneath the Eyedropper Tool. Using the Measure Tool, draw a line along the horizon by clicking, dragging, and then releasing your mouse button. If you don't get your line correct the first time you can just draw another one and it will replace the former line.   Try to include as much of the horizon as you can - this will average out small inconsistencies due to waves, objects on the skyline, etc.

Step 3: To perform the rotation, simply select Image > Rotate Canvas > Arbitrary from the main menu.  The Measure Tool will have already entered in the correct angle of rotation for us.  Just make sure that the direction of rotation is set correctly (i.e. either clockwise or counter-clockwise), and press OK to rotate your image.

Step 4: Now that you have the results of your rotation, complete with corrected horizon, all you need to do is knock out the black areas with the Crop Tool, a skilfully-used border, or even the Clone Stamp Tool.  Have fun!