# Image warping

Image warping

Image warping is the process of digitally manipulating an image such that any shapes portrayed in the image have been significantly distorted. Warping may be used for correcting image distortion as well as for creative purposes (e.g., morphing [Beier, Thaddeus. [http://www.hammerhead.com/thad/morph.html Feature-Based Image Metamorphosis] . Siggraph '92] ). The same techniques are equally applicable to video.

Overview

While an image can be transformed in various ways, pure warping means that points are mapped to points without changing the colors. This can be based mathematically on any function from (part of) the plane to the plane. If the function is injective the original can be reconstructed. If the function is a bijection any image can be inversely transformed.

The following list is not meant to be a partitioning of all available methods into categories.
*Images may be distorted through simulation of optical aberrations.
*Images may be viewed as if they had been projected onto a curved or mirrored surface. (This is often seen in raytraced images.)
*Images can be partitioned into polygons and each polygon distorted.
*Images can be distorted using morphing.

There are at least two ways to generate an image using whatever chosen methods to distort.
*(forward-mapping) a given mapping from sources to images is directly applied
*(reverse-mapping) for a given mapping from sources to images, the source is found from the image

To estimate what kind of warping has taken place between consecutive images, one can use optical flow estimation techniques.

In the news

In 2007, a suspected pedophile used the "swirl" effect to hide his face in the pictures he had taken while raping and sexually abusing young children whose "ages appear to range from six to early teens." [cite news|url=http://thelede.blogs.nytimes.com/2007/10/08/interpol-untwirls-a-suspected-pedophile/?hp
accessdate=2008-08-25
title=Interpol Untwirls a Suspected Pedophile
page=The Lede
work=New York Times Blog
date=2007-10-08
first=Mike
last=Nizza
] Interpol trivially reversed the swirl by swirling in the opposite direction to identify and eventually locate the man in Thailand.

ee also

*Anamorphosis

References

* Pröfrock, Dima [http://139.30.207.13/index.php?id=wamo Warping/Morphing of Videos] running study to estimate the maximal possible strength of warping of videos without visible quality degradation.
* McMillan, Leonard [http://www.cs.unc.edu/~ibr/pubs/mcmillan-diss/mcmillan-diss.pdf “An Image-Based Approach to Three-Dimensional Computer Graphics”] , "Dissertation", 1997

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