Color mapping is a
function 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 assoc ...
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-dimensio ...
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 problems or to perform a computation. Algorithms are used as specifications for performing ...
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
In digital photography, computer-generated imagery, and colorimetry, a grayscale image is one in which the value of each pixel is a single sample representing only an ''amount'' of light; that is, it carries only intensity information. Gray ...
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 s ...
correspondence between the images.
An example of an algorithm that employs the statistical properties of the images is
histogram matching. 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 '' ari ...
and the
standard deviation of
Lab
Lab most often refers to:
* Laboratory, a facility to conduct scientific research
Lab or LAB may also refer to:
Places
* Láb, a village near Bratislava in western Slovakia
* Lab (river), in north-eastern Kosovo
People
* ISO 639 code for the an ...
channels of the two images.
[Color Transfer between Images](_blank)
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A common algorithm for computing the color mapping when the pixel correspondence is given is building the joint-histogram (see also co-occurrence matrix) 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.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 Interdisciplinarity, 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 t ...
applications. Many applications simultaneously process two or more images and, therefore, need their colors to be calibrated. Examples of such applications are:
Image differencing,
registration,
object recognition, 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 ...
,
co-segmentation and
stereo reconstruction.
See also
*
List of colors
These are the lists of colors;
* List of colors: A–F
* List of colors: G–M
* List of colors: N–Z
* List of colors (compact)
* List of colors by shade
* List of color palettes
* List of Crayola crayon colors
* List of RAL colors
* List ...
*
Color chart
A color chart or color reference card is a flat, physical object that has many different color samples present. They can be available as a single-page chart, or in the form of swatchbooks or color-matching fans.
Typically there are two diffe ...
*
Color management
In digital imaging systems, color management (or colour management) is the controlled conversion between the color representations of various devices, such as image scanners, digital cameras, monitors, TV screens, film printers, computer printe ...
*
ICC profile
In color management, an ICC profile is a set of data that characterizes a color input or output device, or a color space, according to standards promulgated by the International Color Consortium (ICC). Profiles describe the color attributes of ...
*
IT8
*
Optical transfer function
The optical transfer function (OTF) of an optical system such as a camera, microscope, human eye, or projector specifies how different spatial frequencies are captured or transmitted. It is used by optical engineers to describe how the optics pro ...
References
{{color topics
Image processing
Color
Digital imaging