Correcting image distortion, perspective and converging verticals

Barrel distortion correction

Quite a few image stitching tools are capable of correcting linear distortion in images (whether concave or convex distortion, such as the barrel distortion in poor quality rectilinear lenses or in fisheye lenses).

You may also find the following software useful for correcting linear distortion including barrel distortion:

  • Helmut Dersch's PanoTools
  • LensDoc (from Andromeda Software) - also does barrel distortion correction

Please note that this list is not intended to be exhaustive.

Perspective correction

If you have software such as Adobe PhotoShop (see below) you can correct converging verticals using that. If you don't or if you find that that is too difficult, some commercial software and PhotoShop filters may help.

Please note that this list is not intended to be exhaustive.

Perspective correction in Adobe PhotoShop 5.x+

Text and images contributed by: Chris Longhurst

In Adobe PhotoShop 5.x and higher, there's a useful in-built ability to remove the perspective from an image. This is very useful to 3D computer graphics modellers because it means they can extract rectilinear texture maps from almost any photograph. But it can also be useful for panoramic photography.

Let's say you've taken a bunch of images, and in a couple of them there's some tall building. In most cases, these will suffer from converging verticals, and that can mess up some panorama software. Look at the example below - it's an extreme example, but it serves well to demonstrate this method.

Load the image into photoshop, and select the 'crop' tool. In the tools options, there's a new tickbox now entitled "Perspective"

The crop tool The perspective option

Using the crop tool, drag a bounding area into the image, and now, because of the perspective option, you can drag each corner of the bounding area around. This means you can align the edges of the bounding area with any edges in the photo that you know should be vertical or horizontal.

Drag a bounding volume into the photo Align the edges with edges in the image by
adjusting the corner points

When you now hit 'enter' or accept the action, photoshop will make those four corner points become the four corners of a new rectangular image. Voila : you've removed the perspective from the image.

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