Removing Lens Distortion

For your final image-enhancement exercise, you will learn to remove a commonly occurring digital camera image malady: lens distortion. Images shot with a wide-angle lens often exhibit lens distortion. In the following example, you will remove some horizon warping that was applied to a landscape shot with a wide-angle digital camera lens:

1. Open and duplicate the image with the horizon is warped by  the wide-angle view.

2. The remedy for this is simpler than you might think. Choose Filter --> Distort --> Lens Correction. The Lens Correction dialog box appears with an orthogonal set of grid lines laid over the image. There are a variety of lens variables to configure, including distortion, transformation, and chromatic aberration. You can even add and subtract vignetting if you like. For this correction, and for many such corrections, all you will need is the grid system and your eyes.

3. Now identify a linear feature that you think should be horizontal; the base of the tree line in the distance is a good one here.

4. To remove the warping from the image, simply click the image near the tree line and drag the image down until the tree line is horizontal with one of the grid lines. You can hide and show the grid lines by selecting and deselecting the Show Grid check box just below the lower-right edge of the preview area. Click OK to apply the distortion correction.

5. The distortion correction is applied to the image, and as with the canvas rotation you applied earlier, Photoshop must add some pixels to this image. The best way to deal with this is to include as much of the image as possible when cropping, without adding any surrounding white pixels.

6. There is one final step to complete this process. Using this lens distortion filter creates transparency in the image. Therefore, this image needs to be flattened to simplify it. Click the Layers palette menu and choose Flatten to remove the transparency.