Restoring Images on the Computer

This post describes some methods for using the computer to restore anamorphic images. They are not always perfect restorations, but can sometimes reveal the images in ways not easily seen by conventional optical means. In some cases gross errors can also occur if the wrong method is used.

Plane anamorphoses
There are methods using ray tracing programs like POV-Ray which allow you to look at the image from the correct point, but they are too complicated to describe here.

Many people, think that you can just squash the image, that is the reverse of stretching it, but to do so gives wildly incorrect results.

The picture above shows the effect of making the outer ellipse in the Scrots portrait of Edward VI circular. Although the face is recognisable, the text on the left (showing his age is 9) is nowhere near the shape of the text on the right (it is so small it appears blurred in this reproduction). Compare this with the correct restoration in the post above about plane anamorphoses.

Cylindrical Mirror anamorphoses

Most cylindrical mirror anamorphoses are approximated by a mapping from a square grid to a set of circles. This makes it easy to reverse the process with a computer. The result is not always perfect for two reasons. The anamorphosis may have been created using a more precise method than a simple set of circles. It may also have been created by eye and may not be perfect. However, the results are close enough to show the original image almost perfectly, and often to gain a better view than looking in the mirror.

Software to use

Adobe Photoshop has a filter for Polar Coordinates in the Distort options. The Gimp (which is a free program) has a similar filter.

The Wheelbarrow man example is from The Magic Mirror © Dover Books 1979 showing ” A fat man wheeling his stomach in a wheelbarrow”.  The restored image looks like this:

The image below  is an eighteenth century anamorphosis musing on the transitory nature of life mirrored as an illusion. The restored version is at the right.

2 responses to “Restoring Images on the Computer

  1. very very intersting and very much helpful. thanks

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