Super-resolution are techniques that enhance the resolution

Image resolution

Image resolution is an umbrella term that describes the detail an image holds. The term applies to raster digital images, film images, and other types of images. Higher resolution means more image detail....

 of an imaging

Digital imaging

Digital imaging or digital image acquisition is the creation of digital images, typically from a physical scene. The term is often assumed to imply or include the processing, compression, storage, printing, and display of such images...

 system. Some SR techniques break the diffraction-limit

Diffraction-limited

The resolution of an optical imaging system — a microscope, telescope, or camera — can be limited by factors such as imperfections in the lenses or misalignment. However, there is a fundamental maximum to the resolution of any optical system which is due to diffraction...

 of systems, while other SR techniques improve over the resolution of digital imaging sensor

Image sensor

An image sensor is a device that converts an optical image into an electronic signal. It is used mostly in digital cameras and other imaging devices...

.

There are both single-frame and multiple-frame variants of SR. Multiple-frame SR use the sub-pixel shifts between multiple low resolution images of the same scene. They create an improved resolution image fusing information from all low resolution images, and the created higher resolution images are better descriptions of the scene. Single frame SR methods attempt to magnify the image without introducing blur. These methods use other parts of the low resolution images, or other unrelated images, to guess what the high resolution image should look like. Algorithms can also be divided by their domain: frequency

Frequency domain

In electronics, control systems engineering, and statistics, frequency domain is a term used to describe the domain for analysis of mathematical functions or signals with respect to frequency, rather than time....

 or space domain. Originally super-resolution methods worked well only on grayscale images, but researchers have found methods to adapt them to color camera images. Recently also the use of super-resolution for 3D data has been shown

The necessity of aliasing

In the most common SR algorithm

Algorithm

In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...

s, the information that was gained in the SR-image

Image

An image is an artifact, for example a two-dimensional picture, that has a similar appearance to some subject—usually a physical object or a person.-Characteristics:...

 was embedded in the LR images in the form of aliasing

Aliasing

In signal processing and related disciplines, aliasing refers to an effect that causes different signals to become indistinguishable when sampled...

. This requires that the capturing sensor

Sensor

A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...

 in the system is weak enough so that aliasing is actually happening. A diffraction-limited system contains no aliasing, nor does a system where the total system Modulation Transfer Function is filtering

Filter (signal processing)

In signal processing, a filter is a device or process that removes from a signal some unwanted component or feature. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspect of the signal...

 out high-frequency content.

Breaking the diffraction limit

There are also SR techniques that extrapolate

Extrapolation

In mathematics, extrapolation is the process of constructing new data points. It is similar to the process of interpolation, which constructs new points between known points, but the results of extrapolations are often less meaningful, and are subject to greater uncertainty. It may also mean...

 the image in the frequency domain, by assuming that the object on the image is an analytic function

Analytic function

In mathematics, an analytic function is a function that is locally given by a convergent power series. There exist both real analytic functions and complex analytic functions, categories that are similar in some ways, but different in others...

, and that we can exactly know the function

Function (mathematics)

In mathematics, a function associates one quantity, the argument of the function, also known as the input, with another quantity, the value of the function, also known as the output. A function assigns exactly one output to each input. The argument and the value may be real numbers, but they can...

 values in some interval

Interval

Interval may refer to:* Interval , a range of numbers * Interval measurements or interval variables in statistics is a level of measurement...

. This method is severely limited by the noise that is ever-present in digital imaging systems, but it can work for radar

Radar

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...

, astronomy

Astronomy

Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

 or microscopy

Microscope

A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...

.

Other related work

• W.-S. Chan, E. Lam, M. Ng, and G. Mak, "Super-resolution reconstruction in a computational compound-eye imaging system,” Multidimensional Systems and Signal Processing, 18(2–3), pp. 83–101, 2007. http://www.springerlink.com/content/9r2t3r817v649202/
• M. Ng, H. Shen, E. Lam, and L. Zhang, “A total variation regularization based super-resolution reconstruction algorithm for digital video,” EURASIP Journal on Advances in Signal Processing, ID 74585, 2007. http://www.hindawi.com/journals/asp/2007/074585.abs.html
• D. Glasner, S. Bagon, and M. Irani, "Super-Resolution from a Single Image", International Conference on Computer Vision (ICCV), October 2009. example and results

External links

• Super-resolution methods comparison — Comparison tests of several super-resolution algorithms, with lab test charts and real-life photographs.
• UCSC-MDSP RESOLUTION ENHANCEMENT SOFTWARE — A MATLAB implementation of several algorithms on Color and B&W data sets.
• SR GUI in Matlab — Super-resolution software that includes both geometric and photometric registration (only for Windows).
• Video super-resolution using video epitomes.
• EPFL-LCAV — a MATLAB implementation of several SR algorithms.
• Super-resolution FAQ — How it works, an illustrated description.
• Video super-resolution example — A real-life example of super-resolution applied to video.
• What is super-resolution? – an article with step-by-step example of 4x video upsizing using super resolution approach.