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 associ ...
s of one (source)
image 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 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 ...
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 '' ar ...
and the
standard deviation of
Lab channels of the two images.
[Color Transfer between Images](_blank)
/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) 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.
...
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 ite ...
.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 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 human ...
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,
co-segmentation and
stereo reconstruction
In computer vision and computer graphics, 3D reconstruction is the process of capturing the shape and appearance of real objects.
This process can be accomplished either by active or passive methods. If the model is allowed to change its shape ...
.
See also
*
List of colors
*
Color chart
*
Color management
*
ICC profile
*
IT8
IT8 is a set of American National Standards Institute (ANSI) standards for color communications and control specifications. Formerly governed by the IT8 Committee, IT8 activities were merged with those of the Committee for Graphics Arts Technolog ...
*
Optical transfer function
References
{{color topics
Image processing
Color
Digital imaging