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{{Short description|Field of depth extension}}
In [[optics]] and [[signal processing]], '''wavefront coding''' refers to the use of a phase modulating element in conjunction with [[deconvolution]] to extend the [[depth of field]] of a digital imaging system such as a video camera.

Wavefront coding falls under the broad category of [[computational photography]] as a technique to enhance the depth of field.

==Encoding==
The wavefront of a light wave passing through the camera system is modulated using optical elements that introduce a spatially varying optical path length. The modulating elements must be placed at or near the plane of the aperture stop or pupil so that the same modulation is introduced for all field angles across the field-of-view. This modulation corresponds to a change in complex argument of the [[pupil function]] of such an imaging device, and it can be engineered with different goals in mind: e.g. extending the depth of focus.

===Linear phase mask===

Wavefront coding with linear phase masks works by creating an optical transfer function that encodes distance information.<ref name=LinearPhasePatent>[http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=7218448 US Patent 7218448 - Extended depth of field optical systems]</ref>

===Cubic phase mask===

Wavefront Coding with cubic phase masks works to blur the image uniformly using a cubic shaped [[waveplate]] so that the intermediate image, the optical transfer function, is out of [[Focus (optics)|focus]] by a constant amount. [[Digital image processing]] then removes the blur and introduces noise depending upon the physical characteristics of the processor. [[Dynamic range]] is sacrificed to extend the depth of field depending upon the type of filter used. It can also correct [[optical aberration]].<ref name=StanfordPaper>[http://graphics.stanford.edu/courses/cs448a-06-winter/dowski-wavefront-coding-optics95.pdf Extended depth of field through wave-front coding]</ref>

The mask was developed by using the [[ambiguity function]] and the [[stationary phase method]]

==History==

The technique was pioneered by [[radar]] engineer [[Edward Dowski]] and his thesis adviser [[Thomas Cathey]] at the [[University of Colorado at Boulder|University of Colorado]] in the United States in the 1990s. The University filed a patent on the invention.<ref>{{cite web | url=https://patents.google.com/patent/US5748371A/en | title=Extended depth of field optical systems }}</ref> Cathey, Dowski and Merc Mercure founded a company to [[commercialize]] the method called [[CDM-Optics]], and licensed the invention from the University. The company was acquired in 2005 by [[OmniVision Technologies]], which has released wavefront-coding-based mobile camera chips as [[TrueFocus]] sensors.

TrueFocus sensors are able to simulate older autofocus technologies that use rangefinders and narrow depth of fields.<ref name=TrueFocusPatent>[http://www.freepatentsonline.com/y2006/0269150.html Multi-matrix depth of field image sensor]</ref> In fact, the technology theoretically allows for any number of combinations of focal points per pixel for effect. It is the only technology not limited to EDoF (Extended-Depth-of-Field).

==References==
<references/>

==External links==
* [http://lfw.pennnet.com/Articles/Article_Display.cfm?Section=ARTCL&ARTICLE_ID=197348&VERSION_NUM=1 Wavefront coding finds increasing use] (Laser Focus World)

[[Category:Signal processing]]

Wavefront coding - Revision history

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