3-9 : Correcting Lens & Image Distortion

Intro
I'm sure you've seen photos of tall buildings and noticed the walls lean in at the top. This is a common effect that happens when you take photos and although the photo records the perspective, it's not always a desirable look. Photoshop allows you to correct this quite easily. You can also distort the image in other ways and I'll show you the common methods.

Perspective
Below is a photo I took of the Scottish Rite Building (Masons) building in Washington DC. It gives a good idea of what perspective looks like. I took this with a wide angle lens which accented the effect. If you move your mouse over the image, you can see how I have corrected the distortion.

As you can see, I can't retain the full scope of the image, but I can get a less distorted look.

Here is a sample image if you need one for this tutorial.

In this case there is a lot of correction that can be applied, so I am first going to increase the Canvas Size. This changes the working space, without affecting the image. To do this navigate to Image > Canvas Size. You'll see a dialog box pop up and enter the numbers and check the boxes you see below.

By making this setting you are making the canvas larger to the top and the sides, your image will be anchored to the middle of the bottom of the page. By clicking in the square indicated with red, you define the direction of the resize. Now you should have a large area around the image using the color of the background.

Use the magic wand by clicking in the new background area to select the background and it should selected everything but the image. Then create the inverse selection (Select > Inverse).

With the image selected you can start the transformation. Navigate to Edit > Transform > Perspective. Now pick on one of the grips in the top left or right and pull it out to the side until you straighten the pillars and press Enter.

Next you can pull the image up to make the pillars taller. Navigate to Edit > Transform > Scale (or press CTRL+T). Now grab the box that is top-center and pull it up so that have a height that you like.

One problem you'll find with transforming images is that you can end up enlarging the image and losing quality. Try to start with the largest, clearest image you can. The Transform tool has other options (so far you've used Perspective and Scale). The only other one you might use in with photos is Distort. Distort allows you to grab a corner box and pull it in any direction. You'll use Distort when you don't have true perspective to work with.

Here's a sample image to use for trying out the distort transformation. See if you can make the building look a little more square with this tool. Press CTRL+A (Select All) to select the whole image, then navigate to Edit > Transform > Distort. Now you can click on any of the grips to make the adjustments you desire.

Lens Correction Filter in Photoshop

A lot times you might need to make some slight corrections

Conclusion
This may not be a technique that you will use a lot, but it can come in very handy. You might take a photo of a room and have walls that appear tilted - these techniques can be used to fix it. Look for images that can be fixed like this. Remember that you will be sacrificing some areas to make the corrections, and plan accordingly.

Reference
See how perspective works.
Read about how a Tilt-Shift Lens fixes perspective.

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