Color mapping is a

function Function or functionality may refer to: Computing * Function key, a type of key on computer keyboards * Function model, a structured representation of processes in a system * Function object or functor or functionoid, a concept of object-oriente ...

that maps (transforms) the

color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...

s of one (source)

image An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensiona ...

to the colors of another (target) image. A color mapping may be referred to as the

algorithm In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific Computational problem, problems or to perform a computation. Algorithms are used as specificat ...

that results in the mapping function or the algorithm that transforms the image colors. Color mapping is also sometimes called ''color transfer'' or, when grayscale images are involved, ''brightness transfer function (BTF)''; it may also be called ''photometric camera calibration'' or ''radiometric camera calibration''.

Algorithms

There are two types of color mapping algorithms: those that employ the statistics of the colors of two images, and those that rely on a given

pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the smal ...

correspondence between the images. An example of an algorithm that employs the statistical properties of the images is

histogram matching In image processing, histogram matching or histogram specification is the transformation of an image so that its histogram matches a specified histogram. The well-known histogram equalization method is a special case in which the specified histogra ...

. This is a classic algorithm for color mapping, suffering from the problem of sensitivity to image content differences. Newer statistic-based algorithms deal with this problem. An example of such algorithm is adjusting the

mean There are several kinds of mean in mathematics, especially in statistics. Each mean serves to summarize a given group of data, often to better understand the overall value (magnitude and sign) of a given data set. For a data set, the ''arithme ...

and the

standard deviation In statistics, the standard deviation is a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean (also called the expected value) of the set, while ...

of Lab channels of the two images.Color Transfer between Images
/ref> A common algorithm for computing the color mapping when the pixel correspondence is given is building the joint-histogram (see also

co-occurrence matrix A co-occurrence matrix or co-occurrence distribution (also referred to as : ''gray-level co-occurrence matrices'' GLCMs) is a matrix that is defined over an image to be the distribution of co-occurring pixel values (grayscale values, or colors) at ...

) of the two images and finding the mapping by using

dynamic programming Dynamic programming is both a mathematical optimization method and a computer programming method. The method was developed by Richard Bellman in the 1950s and has found applications in numerous fields, from aerospace engineering to economics. I ...

based on the joint-histogram values. When the pixel correspondence is not given and the image contents are different (due to different point of view), the statistics of the image corresponding regions can be used as an input to statistics-based algorithms, such as histogram matching. The corresponding regions can be found by detecting the corresponding

features Feature may refer to: Computing * Feature (CAD), could be a hole, pocket, or notch * Feature (computer vision), could be an edge, corner or blob * Feature (software design) is an intentional distinguishing characteristic of a software item ...

.Piecewise-consistent Color Mappings of Images Acquired Under Various Conditions

Applications

Color mapping can serve two different purposes: one is calibrating the colors of two cameras for further processing using two or more sample images, the second is adjusting the colors of two images for perceptual visual compatibility.

Color calibration The aim of color calibration is to measure and/or adjust the color response of a device (input or output) to a known state. In International Color Consortium (ICC) terms, this is the basis for an additional color characterization of the device ...

is an important pre-processing task in

computer vision Computer vision is an interdisciplinary scientific field that deals with how computers can gain high-level understanding from digital images or videos. From the perspective of engineering, it seeks to understand and automate tasks that the hum ...

applications. Many applications simultaneously process two or more images and, therefore, need their colors to be calibrated. Examples of such applications are:

Image differencing Image differencing is an image processing technique used to determine changes between images. The difference between two images is calculated by finding the difference between each pixel in each image, and generating an image based on the result. Fo ...

registration Register or registration may refer to: Arts entertainment, and media Music * Register (music), the relative "height" or range of a note, melody, part, instrument, etc. * ''Register'', a 2017 album by Travis Miller * Registration (organ), th ...

object recognition Object recognition – technology in the field of computer vision for finding and identifying objects in an image or video sequence. Humans recognize a multitude of objects in images with little effort, despite the fact that the image of the ...

, multi-camera

tracking Tracking may refer to: Science and technology Computing * Tracking, in computer graphics, in match moving (insertion of graphics into footage) * Tracking, composing music with music tracker software * Eye tracking, measuring the position of t ...

, co-segmentation and stereo reconstruction.

References

{{color topics Image processing Color Digital imaging

Algorithms

Applications

See also

References