HCL ( Hue- Chroma-

Luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls with ...

) or LCh refers to any of the many cylindrical color space models that are designed to accord with human perception of color with the three parameters. Lch has been adopted by

information visualization Information is an abstract concept that refers to that which has the power to inform. At the most fundamental level information pertains to the interpretation of that which may be sensed. Any natural process that is not completely random, a ...

practitioners to present data without the bias implicit in using varying

saturation Saturation, saturated, unsaturation or unsaturated may refer to: Chemistry * Saturation, a property of organic compounds referring to carbon-carbon bonds **Saturated and unsaturated compounds ** Degree of unsaturation **Saturated fat or fatty aci ...

. They are, in general, designed to have characteristics of both cylindrical translations of the

RGB color space An RGB color space is any additive color space based on the RGB color model. An RGB color space is defined by chromaticity coordinates of the red, green, and blue additive primaries, the white point which is usually a standard illuminant, an ...

, such as

HSL and HSV HSL (for hue, saturation, lightness) and HSV (for hue, saturation, value; also known as HSB, for hue, saturation, brightness) are alternative representations of the RGB color model, designed in the 1970s by computer graphics researchers to mor ...

, and the L*a*b* color space. Some conflicting definitions of the terms are: * A name for a cylindrical transformation of CIELuv (CIELCh_uv) employed by Ihaka (2003) and adopted by Zeileis et al. (2009, 2020). This name appears to be the one most commonly used in information visualization. Ihaka, Zeileis, and co-authors also provide software implementations and web pages to promote its use. * A name for cylindrical CIELab (CIELCh_ab), employed by chroma.js. * "HCL" designed in 2005 by Sarifuddin and Missaou, which is a transformation of whatever type of RGB color space is in use.
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Derivation

Color-making attributes

HCL concerns the following attributes of color appearance: ; Hue: The "attribute of a visual sensation according to which an area appears to be similar to one of the perceived colors: red, yellow, green, and blue, or to a combination of two of them". ;

Lightness Lightness is a visual perception of the luminance (L) of an object. It is often judged relative to a similarly lit object. In colorimetry and color appearance models, lightness is a prediction of how an illuminated color will appear to a stan ...

, value: The "brightness relative to the brightness of a similarly illuminated white". ;

(''Y'' or ''L''_v,Ω): The radiance weighted by the effect of each wavelength on a typical human observer, measured in SI units in candela per square meter (). Often the term ''luminance'' is used for the

relative luminance Relative luminance Y follows the photometric definition of luminance L including spectral weighting for human vision, but while luminance L is a measure of light in units such as cd/m^2, Relative luminance Y values are normalized as 0.0 to 1.0 ...

, ''Y''/''Y''_''n'', where ''Y''_''n'' is the luminance of the reference

white point A white point (often referred to as reference white or target white in technical documents) is a set of tristimulus values or chromaticity coordinates that serve to define the color "white" in image capture, encoding, or reproduction. Depending ...

. ;

Colorfulness Colorfulness, chroma and saturation are attributes of perceived color relating to chromatic intensity. As defined formally by the International Commission on Illumination (CIE) they respectively describe three different aspects of chromati ...

: The "attribute of a visual sensation according to which the perceived color of an area appears to be more or less chromatic". The HSL and HSV color spaces are more intuitive translations of the RGB color space, because they provide a single hue number. However, their luminance variation does not match the way humans perceive color.

Perceptually uniform In color science, color difference or color distance is the separation between two colors. This metric allows quantified examination of a notion that formerly could only be described with adjectives. Quantification of these properties is of great ...

color spaces outperform RGB in cases such as high noise environments.

CIE color spaces

CIE-based LCh color spaces are transformations of the two chroma values (ab or uv) into the polar coordinate. The source color spaces are still very well-regarded for their uniformity, and the transformation does not cause degradation in this aspect. See the respective articles for how the underlying coordinates are derived.

Sarifuddin 2005

Sarifuddin, noting the lack of blue hue consistency of CIELAB—a common complaint among its users— decided to make their own color space by mashing up some of the features. According to the

Stack Overflow In software, a stack overflow occurs if the call stack pointer exceeds the stack bound. The call stack may consist of a limited amount of address space, often determined at the start of the program. The size of the call stack depends on many facto ...

user Tatarize, what Sarifuddin proposes as "HCL" is algorithmically similar to HSL. While pointing out advantages in computational efficiency, they argue that Sarifuddin's work does not represent a significant improvement over the CIELAB color space while showing failure to reproduce the paper's claims. They also propose what they consider to be an improved version of Sarifuddin's algorithm.

Other color appearance models

In general, any

color appearance model A color appearance model (CAM) is a mathematical model that seeks to describe the perceptual aspects of human color vision, i.e. viewing conditions under which the appearance of a color does not tally with the corresponding physical measurement o ...

with a lightness and two chroma components can also be transformed into a HCL-type color space by turning the chroma components into polar coordinates.

Implementations

CIELCh has been implemented in a wide range of ways: as programmatic code for generating color swatches in statistics tools, as standalone tools for designing and testing swatches, or as libraries that allow other programs to use the color space. Some implementations include: * Statistical tools: **

d3.js D3.js (also known as D3, short for Data-Driven Documents) is a JavaScript library for producing dynamic, interactive data visualizations in web browsers. It makes use of Scalable Vector Graphics (SVG), HTML5, and Cascading Style Sheets (CSS) sta ...

: Data Driven Documents JavaScript library (CIELCh_ab) * Swatch designs: ** The colorspace package for the R and the Python programming languages, also with pre-made sets of swatches in hclwizard ** Fabio Crameri's scientific colour maps, a set of pre-made swatches * Library: ** The aforementioned colorspace library (CIELCh_uv) ** ac-colors JavaScript library (CIELCh_ab and CIELCh_uv) ** chroma.js JavaScript library (CIELCh_ab) ** colorio for Python ** Most other color space libraries handle at least one of CIELUV or CIELAB

References

External links

HCL Wizard online color apps

colorspace: HCL-Based Color Tools and Palettes in R

Generating random colors

How To Avoid Equidistant HSV Colors

{{color space, state=expanded Color space