Wavefront coding
Encyclopedia
In optics
and signal processing
, wavefront coding is a method for creating optical transfer function
s of lenses
with specially designed phase masks, encoding, to produce point spread function
s of visible light, images, with manipulatable information such as depth of field
and distance
.
Wavefront coding falls under the broad category of computational photography
as a technique to enhance the depth of field.
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.
The mask was developed by using the ambiguity function and the stationary phase method
engineer Edward Dowski and his thesis adviser Thomas Cathey at the University of Colorado
in the United States in the 1990s. After the university showed little interest in the research they have since founded a company to commercialize the method called CDM-Optics. 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. In fact, the technology theoretically allows for any number of combinations of focal points per pixel for effect. Currently, it is the only technology not limited to EDoF (Extended-Depth-of-Field).
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
and signal processing
Signal processing
Signal processing is an area of systems engineering, electrical engineering and applied mathematics that deals with operations on or analysis of signals, in either discrete or continuous time...
, wavefront coding is a method for creating optical transfer function
Optical transfer function
The optical transfer function of an imaging system is the true measure of resolution that the system is capable of...
s of lenses
Lens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
with specially designed phase masks, encoding, to produce point spread function
Point spread function
The point spread function describes the response of an imaging system to a point source or point object. A more general term for the PSF is a system's impulse response, the PSF being the impulse response of a focused optical system. The PSF in many contexts can be thought of as the extended blob...
s of visible light, images, with manipulatable information such as depth of field
Depth of field
In optics, particularly as it relates to film and photography, depth of field is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image...
and distance
Distance
Distance is a numerical description of how far apart objects are. In physics or everyday discussion, distance may refer to a physical length, or an estimation based on other criteria . In mathematics, a distance function or metric is a generalization of the concept of physical distance...
.
Wavefront coding falls under the broad category of computational photography
Computational photography
Computational imaging refers to any image formation method that involves a digital computer. Computational photography refers broadly to computational imaging techniques that enhance or extend the capabilities ofdigital photography...
as a technique to enhance the depth of field.
Linear phase mask
Wavefront Coding with linear phase masks works by creating an optical transfer function that encodes distance information.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 focusFocus (optics)
In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by...
by a constant amount. Digital image processing
Digital image processing
Digital image processing is the use of computer algorithms to perform image processing on digital images. As a subcategory or field of digital signal processing, digital image processing has many advantages over analog image processing...
then removes the blur and introduces noise depending upon the physical characteristics of the processor. Dynamic range
Dynamic range
Dynamic range, abbreviated DR or DNR, is the ratio between the largest and smallest possible values of a changeable quantity, such as in sound and light. It is measured as a ratio, or as a base-10 or base-2 logarithmic value.-Dynamic range and human perception:The human senses of sight and...
is sacrificed to extend the depth of field depending upon the type of filter used. It can also correct optical aberration.
The mask was developed by using the ambiguity function and the stationary phase method
History
The technique was pioneered by radarRadar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
engineer Edward Dowski and his thesis adviser Thomas Cathey at the University of Colorado
University of Colorado at Boulder
The University of Colorado Boulder is a public research university located in Boulder, Colorado...
in the United States in the 1990s. After the university showed little interest in the research they have since founded a company to commercialize the method called CDM-Optics. The company was acquired in 2005 by OmniVision Technologies
OmniVision Technologies
OmniVision Technologies Inc. is a corporation that designs and develops digital imaging products. Headquartered in Santa Clara, California, OmniVision Technologies has offices in the USA, Western Europe and Asia, including a design center and testing facility in Shanghai, China. The company...
, 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. In fact, the technology theoretically allows for any number of combinations of focal points per pixel for effect. Currently, it is the only technology not limited to EDoF (Extended-Depth-of-Field).
External links
- Applications, with sample pictures
- CDM-Optics
- Wavefront coding finds increasing use (Laser Focus World)
- Wikinvest's OmniVision Technologies article