What is a Computational Camera?
(a) The traditional camera model, which is based on the camera
obscura. (b) A computational camera uses optical coding followed by
computational decoding to produce new types of images. (c) A
programmable imaging system is a computational camera whose optics
and software can be varied/controlled. (d) The optical coding can
also be done via illumination by means of a programmable flash.
|February 2003. Revised: January 2011|
1. Evolution of the Camera Model
The Traditional Camera
Over the last century, the evolution of the camera has been truly remarkable.
However, through this evolution the basic model underlying the camera has
remained essentially the same, namely, the camera obscura (Figure 1(a)). The traditional camera has a detector and a standard
lens which only captures those principal rays that pass through its center of
projection, or effective pinhole, to produce the familiar linear perspective
image. In other words, the traditional camera performs a very simple and
restrictive sampling of the complete set of rays, or the light field, that
resides in any real scene.
A computational camera (Figure 1(b)) uses a
combination of novel optics and computations to produce the final image. The
novel optics is used to map rays in the light field of the scene to pixels on
the detector in some unconventional fashion. For instance, the ray shown in
Figure 1(b) has been geometrically redirected by the
optics to a different pixel from the one it would have arrived at in the case
of a traditional camera. As illustrated by the change in color from yellow to
red, the ray could also be photometrically altered by the optics. In all cases,
the captured image is optically coded and may not be meaningful in its raw
form. The computational module has a model of the optics, which it uses to
decode the captured image to produce a new type of image that could benefit a
vision system. The vision system could either be a human observing the image or
a computer vision system that uses the image to interpret the scene it
Programmable Computational Cameras
Computational cameras produce images that are fundamentally different from
the traditional linear perspective image. However, the hardware and software of
each computational camera are typically designed to produce a particular type
of image. The nature of this image cannot be altered without significant
redesign of the imaging system.
A programmable imaging system uses an optical system for forming the image,
that can be varied by a controller (Figure 1(c)) in
terms of its radiometric and/or geometric properties. When such a change is
applied to the optics, the controller also changes the decoding software in the
computational module. The result is a single imaging system that can emulate
the functionalities of several specialized ones. Such a flexible camera has two
major benefits. First, a user is free to change the role of the camera based on
his or her needs. Second, it allows us to explore the notion of a purposive
camera that, as time progresses, automatically produces the visual information
that is most pertinent to the task. In order to give its end-user true
flexibility, a programmable imaging system must have an open hardware and
The basic function of the camera flash has remained the same since it first
became commercially available in the 1930s. It is used to brightly illuminate
the camera's field of view during the exposure time of the image detector. It
essentially serves as a point light source. Due to the significant
technological advances made with respect to digital projectors, the time has
arrived for the flash to play a more sophisticated role in the capture of
images. The use of a projector-like source as a camera flash is powerful as it
provides full brightness and color control over time of each of the 2D set of
rays it emits (a projector with a finite aperture actually projects a 4D set of
rays but only permits control over two of the dimensions). This enables the
camera to project arbitrarily complex illumination patterns onto the scene,
capture the corresponding images, and compute information regarding the scene
that is not possible to obtain with the traditional flash. In this case, the
complete imaging system can still be thought of as a computational camera where
captured images are optically coded due to the patterned illumination of the
scene (Figure 1(d)).
An array of cameras and an array of projectors can be used simultaneously to
capture coded measurements of the light field of a scene. Computational
decoding of such measurements can facilitate post-capture control of a variety
of imaging parameters, including, viewpoint, resolution (spatial, temporal,
angular and spectral), depth of field and lighting.
2. Coding Approaches
The design space for the optics of computational cameras is large. It would
be desirable to have a single design methodology that produces an optimized
optical system for any given set of imaging specifications. The optimization
criterion could incorporate a variety of factors, including performance and
complexity. At this point in time, however, such a systematic design approach
does not exist. Consequently, as with traditional optics, the design of
computational cameras remains part science and part art.
The optical coding methods used in today's computational cameras can be
broadly classified into the six approaches shown in Figure 2. The first four of these can be viewed as modifications
to the traditional camera model. Examples of existing computational cameras
that lie in each of the six categories can be found in [Nayar 2011].
Object Side Coding
This is the most convenient way to implement a computational camera, as it
only requires optics to be externally attached to a traditional camera (Figure
2(a)). A few examples of this approach include wide
angle catadioptric imaging, generalized mosaicing and integral imaging using an
externally attached lens or prism array. Object side coding has also been used
to develop a variety of "non-central" cameras that do not have a single
effective viewpoint but rather a locus of viewpoints. In some cases, the locus
of viewpoints is a necessary compromise made to achieve a particular type of
image projection and in other cases, such as panoramic stereo, it is a
Optical coding approaches used in computational cameras. The first four
of these are shown as modifications made to a traditional camera. (a)
Object side coding, where an optical element is attached externally to
a conventional lens. (b) Pupil plane coding, where an optical element
is placed at, or close to, the aperture of the lens. (c) Focal plane
coding, where an optical element is placed at, or close to, the
detector plane. (d) Illumination coding, where coding is achieved by
projecting complex illumination patterns onto the scene. (e) The
imaging system is made up of a cluster or array of traditional camera
modules. (f) A radically different camera design that cannot be
described as a modification to a traditional camera or a collection of
traditional cameras. See [Nayar 2011] for examples of each approach.
Pupil Plane Coding
In this case, an optical element is placed at, or close to, the pupil plane
of a traditional lens (Figure 2(b)). Examples include
the use of phase plates and coded apertures for depth of field extension, the
use of coded apertures for enhancing signal-to-noise ratio and resolution,
aperture and focus control for depth estimation, aperture splitting for dynamic
range extension and image replication, and the use of programmable apertures
for viewpoint control and light field capture.
Focal Plane Coding
Here, an optical element is placed on, or close to, the image detector
(Figure 2(c)). In this approach, we also include the
use of small physical motions of the image sensor or pixel-wise control of
exposure. Examples include the use of lens arrays and attenuation masks for
light field imaging, the use of assorted pixel filters for multispectral and
high dynamic range imaging, and the use of sensor motion to achieve
super-resolution, extended depth of field and motion deblurring.
As mentioned earlier, by using a spatially and/or temporally controllable
flash, captured images can be coded using illumination patterns. This approach
enables image coding in ways that are not possible by only altering the imaging
optics (Figure 2(d)). Illumination coding has a long
history in the field of computer vision - virtually any structured light method
or variant of photometric stereo is based on the notion of illumination coding.
Recent examples include the use of multiplexed illumination for SNR enhancement
and object relighting, and the use of coded illumination patterns for the
measurement of light transport in a scene.
Camera Clusters and Arrays
A number of traditional cameras can be spatially arranged to create new
types of images (Figure 2(e)). In this case, these is no explicit optical
coding involved. One can view this approach as increasing (in space and/or
time) the sampling of the light field. While camera clusters seek to capture
wide fields of view with minimal overlap between the fields of view of adjacent
cameras, camera arrays capture multiple perspectives of the same scene with
large overlap between the fields of view to acquire 3d reconstructions or light
fields of the scene.
Unconventional Imaging Systems
These are optical designs that cannot be easily described as modifications
to, or collections of, traditional cameras (Figure 2(f)). While we have not
seen many well-tested examples of such systems, one can expect novel designs in
the decades to come. Examples may include flexible cameras that can be wrapped
around objects or incorporated into clothing, networked dust cameras that can
be scattered to produce images of volumes of space, and surfaces made of pixels
that can both measure and radiate light.
Computational cameras can be characterized based on the coding approach
they use, the number images they need to capture as input, and the type
of information they produce.
Figure 3 shows a way to characterize computational cameras based on three
factors: (a) the technical approach used for coding, (b) the number of images
that need to be captured, and (c) the type of information produced.
3. Benefits of Computational Cameras
New Imaging Functionalities
One motivation for developing computational cameras is to create new imaging
functionalities that would be difficult, if not impossible, to achieve using
the traditional camera model. The new functionality may come in the form of
images with enhanced field of view, spectral resolution, dynamic range,
temporal resolution, etc. The new functionality can also manifest in terms of
flexibility - the ability to manipulate the optical settings of an image
(focus, depth of field, viewpoint, resolution, lighting, etc.) after the image
has been captured.
Improved Performance-to-Complexity Ratio
Another major benefit of computational imaging is that it enables the
development of cameras with higher performance-to-complexity ratio than
traditional imaging. Camera complexity has yet to be defined in concrete terms.
However, one can formulate it as some function of size, weight and cost. In
traditional imaging, it is generally accepted that higher performance comes at
the cost of complexity. For instance, to increase the resolution of a camera,
one needs to increase the number of elements in its lens - this is the only way
to combat the aberrations that limit resolution. In contrast, computational
imaging allows a designer to shift complexity from hardware to computations.
For instance, high image resolution can be achieved by post-processing an image
captured with very simple optics (even a single element).
4. Limits of Computational Cameras
The design of computational cameras may be viewed as choosing an appropriate
operating point within a high dimensional parameter space. Some of the
parameters are photometric resolution, spatial resolution, temporal resolution,
angular resolution, spectral resolution, field of view and F-number. The space
could include additional parameters related to the "cost" of the design, such
as, size, weight and expense. In general, while making a final design choice to
achieve a desired functionality, one is forced to trade-off between the various
parameters. In short, as with traditional imaging, there is no "free lunch"
with computational cameras. For instance, in the cases of omnidirectional
imaging and integral imaging, resolution is traded-off for wider field of view
and viewpoint (or focus) control, respectively. Generally, the trade-off made
with any given computational camera is straightforward to analyze and
While computational cameras have been shown to enable new imaging
functionalities and achieve high performance-to-complexity ratios, it is not
known whether computational imaging can be used to break fundamental limits of
imaging. For instance, it is not clear that the hard resolution limits imposed
by diffraction can be overcome using computations. This is an open question
that deserves closer attention.
The development of computational cameras lies within the larger field of
computational imaging. While computational imaging encompasses a wide range of
imaging modalities and applications, computational cameras seek to overcome the
limits of the traditional camera and impact all fields that use the camera as a
source of information. Examples of such fields include photography, computer
vision, computer graphics, biometrics, remote sensing and robotics.
One way to define the terms digital photography, computational
photography, computational imaging/cameras and computational image
Figure 4 shows one possible way to define the terms digital photography,
computational photography, computational imaging/cameras and computational
image sensors. The field of computational cameras naturally overlaps the areas
of computational photography and computational image sensors (Figure 5).
Computational photography includes the development of purely software based
methods that seek to process multiple images (which could be taken with even a
traditional camera) to produce a new type of image or scene representation.
With respect to the computational image sensors, several research teams are
developing detectors that can perform image sensing as well as early visual
The four fields defined in Figure 4
are closely related to each other
and overlap significantly in terms of the types of methods they
"Computational Cameras: Convergence of Optics and Processing,"
C. Zhou and S.K. Nayar,
IEEE Transactions on Image Processing,
Vol. 20, No. 12, pp. 3322-3340, Dec. 2011.
[PDF] [bib] [©]
"Computational Cameras: Approaches, Benefits and Limits,"
Technical Report, Department of Computer Science, Columbia University CUCS-001-11,
[PDF] [bib] [©]
"Programmable Imaging: Towards a Flexible Camera,"
S. K. Nayar, V. Branzoi, and T. E. Boult,
International Journal on Computer Vision,
[PDF] [bib] [©]
"Computational Cameras: Redefining the Image,"
S. K. Nayar,
IEEE Computer Magazine, Special Issue on Computational Photography,
pp. 30-38, Aug. 2006.
[PDF] [bib] [©]
Computational cameras and variants
(Plenary talk, ICIP, Thessaloniki, October 2001)
(Symposium on Computational Photography, Boston, May 2005)
Programmable illumination and the convergence of cameras and projectors
(Keynote, Procams Workshop, New York, June 2006)
Approaches to Optical Coding
(Adobe, San Jose, November 2007)
Computational Imaging Projects