Getting perfectly straight or level photos can be hard in some circumstances. Uneven ground or an off-centred camera can result in a crooked photo, and lower its quality. Using Photoshop, we can correct for these errors and create an accurately cantered and well-leveled photo.
Step 1: Opening the Image
Our first step is to open our image that we want to level or straighten out. The photo needs to have some visual elements, that when taking it where straight either horizontal or vertical straight.
For example edges of buildings/structures, horizon lines, etc. which should have a straight edge that we can use as a reference. In my case, I am using the photo below. When taking the photo, the building structure was straight, but unfortunately the ground was not, and I am left with this off-angled photo. However, this building is perfect to use as a reference to adjust my image.
Step 2: Using the "Ruler Tool or Measurement Tool"
Using the Ruler/Measurement tool (I), or within CS5 you can go via the menu: Analysis > Ruler Tool, we want to draw a line along a straight edge that we wish to re-orientate in the photo. I am going to use the edge of this building because I know this should be straight and aligned to the vertical axis.
Clicking and dragging from one point of the edge to the other (as seen below) gives us a line that Photoshop can use and recognise as a line that should be straight.
Step 3: Method One, "Straightening" (CS5)
Using Photoshop's inbuilt method of straightening is one way to correct the photo. With the line drawn and the ruler tool still selected, click the "Straighten" button on the ruler tool menu below the main menu bar. This should automatically straighten the image and accurately fit it to the line you drew. The tool also crops the image for you, removing empty space created by skewing the image in order to get it straight.
Our newly straightened image:
Step 4: Method Two, "Arbitrary Rotate" (CS2+)
Another and just as effective way to fix an image using the ruler tool is to do an arbitrary image rotation. With the line from the ruler tool still drawn on the unlevel photo, apply an "Arbitrary Rotation" (Image > Image Rotation > Arbitrary). Photoshop automatically finds the angle needed to rotate the canvas so the line is perfectly straight, and inputs this into the field. Select "Ok" while leaving the fields as they are.
After cropping out the edges of the photo that are empty due to the rotation, you should have a precisely aligned photo that adds to the overall composition of the image.
Both these methods work well in their own different ways. By experimenting with them, it's possible to get an unlevel photo to look just right. Remember that this method can also be applied along the horizontal axis, with the ground or horizon line being perfect visual points to straighten a photo