In this tutorial, we’re going to look at several ways of correcting distortion in an image. The topics we’ll be covering are image straightening, perspective distortion and lens distortion.
The first, image straightening, is relatively easy to correct. This is where you photograph an image and the horizon appears to be tilted. To fix that, in the Tools toolbar on the left, click on the Straighten tool (6th from the top – make sure to choose the Straighten tool in the flyout).
You’ll see a long bar with handles at either end. To straighten the image, drag the ends of the bar to line up with the place on the image that needs to be straightened.
You should also see the Tool Options – Straighten Tool bar in blue repeated across your workspace. If you don’t see the Straighten options tools, click on the bar to reveal them. These options will tend to appear/disappear, depending on where you are in the image and if you want to access the controls again, you’ll need to click on the blue bar.
In the Mode drop down list, you have three options:
- Auto: Where you place the straightening bar is how the image is straightened.
- Make Vertical : This rotates the image and makes the straightening bar vertical
- Make Horizontal: This rotates the image and makes the straightening bar horizontal
Other options allow you to crop the image, rotate all layers and numerically adjust the angle.
How to Correct Perspective Distortion
This is a common problem and is most obvious with buildings. The end result is that the object appears to be leaning backwards or widens at a particular point.
In this screen shot, you see the building before perspective correction is applied.
There are two ways that you can correct the perspective:
- The Perspective Correction tool
- The Pick Tool
The Perspective Correction tool is designed to be used with a single image, while the Pick tool is meant to be used with layers. Let’s look at the first option. On the Tools toolbar, click the Perspective Correction tool from the flyout.
This places a bounding box on the image. To change the perspective, you’ll want to drag the control points as I’ve done in the image above. You also have a number of options. On the tools palette, you can choose how many grid lines you want to display (I’ve used two). You can also enable the Crop image checkbox. This will crop the image to a rectangular shape. If you don’t want the cropping to take place, uncheck the Crop image checkbox.
The result after the cropping. Most importantly, the vertical and horizontal lines are correct. If you don’t like the result, click on Ctrl+Z or Alt+Backspace to undo it.
Perspective Correction in a Layer
To correct perspective in a layer, click on the layer that you want to correct. Go to View: Grid to show the gridlines, which will help you adjust your image. To adjust the settings, go to View: Change Grid, Guide & Snap Properties. While you can adjust these settings, I left them at the default. Next, because you will be adjusting the size of the image, beyond its current dimensions, go to Image: Canvas Size and add another 200 pixels around the image.
Next, click on the Pick tool, which creates a bounding box around the entire layer. Click on the blue bar which should read: Tool Options – Pick Tool. In the Mode options drop down list, click on Perspective.
Now, hold down the Ctrl key and click on a corner of the bounding box, dragging it inward or outward to change the perspective of the image. The image will update as you finish dragging. You may have to do this a number of times to get the desired result.
For the sake of illustration, I’ve placed a black layer underneath the image and expanded the image canvas. Your results will differ from what you see here.
How to Correct Lens Distortions
Before begin, it’s important to know that lenses can distort your image in a variety of ways, which we’ll look at in a moment. Fortunately, Paintshop Photo Pro offers a number of tools at your disposal.
The most common types of distortion are:
- Barrel Distortion: The photo appears as if it’s bowing out at the center of the image.
- Fisheye Distortion: This is where the image looks like it’s been pasted onto a ball,
- Pincushion Distortion: Makes the photo look like it has a depression in the middle.
To fix these issues, you need to be in the full editor workspace. Depending on which distortion problem you have, click on:
- Adjust: Barrel Distortion Correction
- Adjust: Fisheye Distortion Correction
- Adjust: Pincushion Distortion Correction
For the image above, here are the settings I’ve used in the Barrel Distortion Correction dialog box:
- Preview on Image: On
- Settings: Corner Stretch
- Strength: 100
These settings are quite strong and are necessary to reduce the large amount of distortion. Since each image can vary quite a bit, you’ll need to experiment with the settings to achieve the desired results.
Note: Enabling Preserve central scale allows you to add or remove pixels at the center of the image, which changes the scale.
For the sake of this tutorial, I have only looked at one option, barrel distortion. Be aware that the controls for each distortion dialog are similar, though the results will be different.
This tutorial gives you a quick overview of what you can accomplish using the distortion correction tools. Be aware that you will probably have to experiment with the settings in order to get the desired result.
About the Author
Nathan Segal has been working as a technical writer for 13 years. His specialty is taking complex subjects and turning them into language that anyone can understand. To improve your photography, image processing and results, visit: DigitalArtistU.com