optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultrav ...

and

signal processing Signal processing is an electrical engineering subfield that focuses on analyzing, modifying and synthesizing ''signals'', such as sound, images, and scientific measurements. Signal processing techniques are used to optimize transmissions, ...

, wavefront coding refers to the use of a phase modulating element in conjunction with

deconvolution In mathematics, deconvolution is the operation inverse to convolution. Both operations are used in signal processing and image processing. For example, it may be possible to recover the original signal after a filter (convolution) by using a deco ...

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 Computational photography refers to digital image capture and processing techniques that use digital computation instead of optical processes. Computational photography can improve the capabilities of a camera, or introduce features that were no ...

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 The pupil function or aperture function describes how a light wave is affected upon transmission through an optical imaging system such as a camera, microscope, or the human eye. More specifically, it is a complex function of the position in the pu ...

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.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 A waveplate or retarder is an optical device that alters the polarization state of a light wave travelling through it. Two common types of waveplates are the ''half-wave plate'', which shifts the polarization direction of linearly polarized ligh ...

so that the intermediate image, the optical transfer function, is out of

focus Focus, or its plural form foci may refer to: Arts * Focus or Focus Festival, former name of the Adelaide Fringe arts festival in South Australia Film *''Focus'', a 1962 TV film starring James Whitmore * ''Focus'' (2001 film), a 2001 film based ...

by a constant amount.

Digital image processing Digital image processing is the use of a digital computer to process digital images through an algorithm. As a subcategory or field of digital signal processing, digital image processing has many advantages over analog image processing. It allo ...

then removes the blur and introduces noise depending upon the physical characteristics of the processor.

Dynamic range Dynamic range (abbreviated DR, DNR, or DYR) is the ratio between the largest and smallest values that a certain quantity can assume. It is often used in the context of Signal (electrical engineering), signals, like sound and light. It is measured ...

is sacrificed to extend the depth of field depending upon the type of filter used. It can also correct optical aberration.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 Radar is a detection system that uses radio waves to determine the distance ('' ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, we ...

engineer Edward Dowski and his thesis adviser Thomas Cathey at the

University of Colorado The University of Colorado (CU) is a system of public universities in Colorado. It consists of four institutions: University of Colorado Boulder, University of Colorado Colorado Springs, University of Colorado Denver, and the University o ...

in the United States in the 1990s. The University filed a patent on the invention.{{cite web , url=https://patents.google.com/patent/US5748371A/en , title=Extended depth of field optical systems 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 OmniVision Technologies Inc. is an American subsidiary of Chinese semiconductor device and mixed-signal integrated circuit design house Will Semiconductor. The company designs and develops digital imaging products for use in mobile phones, not ...

, 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.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

External links

Wavefront coding finds increasing use
(Laser Focus World) Signal processing