CAM16 JMh

The CAM16 JMh color space is not registered in Color by default

Properties

Name: cam16-jmh

White Point: D65 / 2˚

Coordinates:

Name	Range^*
`j`	[0, 100]
`m`	[0, 105]
`h`	[0, 360)

^* Space is not bound to the range and is only used as a reference to define percentage inputs/outputs in relation to the Display P3 color space.

The sRGB gamut represented within the CAM16 JMh color space.

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 of the stimulus source.

CAM16 is a successor of CIECAM02 with various fixes and improvements. The model actually defines numerous different attributes:

Name	Description
J	Lightness
C	Chroma
h	hue
s	saturation
Q	Brightness
M	Colorfulness
H	Hue Quadrature

A color space can be constructed of using a subset of these attributes: JCh, JMh, Jsh, QCh, QMh, Qsh, etc. You can also construct Lab like spaces taking using the hue and either C, M, or s. The cam16-jmh color space in ColorAide represents the JMh configuration.

Learn more.

Viewing Conditions

CAM16 is a color appearance model and can be configured with different viewing environments. A CAM16 color space will also have an associated environment object. This environment object determines the viewing conditions. Colors will appear different based on the viewing conditions.

Viewing Conditions	Description
White	This is the white point and should be the same as defined in the color class. This is provided as (x, y) chromaticity coordinates.
Adapting Luminance	The luminance of the adapting field (`La`). The units are in cd/m2.
Background Luminance	The background luminance (`Yb`) the relative luminance of the nearby background (out to 10°), relative to the reference white's luminance (`Y`). Usually 20 providing a gray world assumption.
Surround	A description of the peripheral area. Use "dark" for a movie theater, "dim" for e.g. viewing a bright television in a dimly lit room, or "average" for surface colors.
Discounting	Discounts the illuminant. If true, the eye is assumed to be fully adapted to the illuminant. Otherwise, the degree of discounting is based on other parameters. When the eye is not fully adapted, it can affect the way colors appear and the chromatic response.

ColorAide must provide some defaults, so CAM16 comes with a default set of viewing conditions that uses a D65 white point, an adapting luminance of 64 lux or a value of ~4 cd/m², it uses the "gray world" assumption and sets the background to 20, an "average" surround and leaves discounting set to False. Variants such as CAM16 UCS, CAM16 SCD, and CAM16 LCD assume these same defaults.

The default settings do not have to be used and a new CAM16 variant with different viewing conditions can be created. When doing this, the space should be derived from the default. A UCS variant would be derived from their defaults, etc.

>>> from coloraide import Color as Base
>>> from coloraide.spaces.cam16_jmh import CAM16JMh, Environment
>>> from coloraide.cat import WHITES
>>> from coloraide import util
>>> import math
>>> class CustomCAM16JMh(CAM16JMh):
...     NAME = "cam16-custom"
...     SERIALIZE = ("--cam16-custom",)
...     WHITE = WHITES['2deg']['D65']
...     ENV = Environment(
...         white=WHITE,
...         adapting_luminance=1000 / math.pi,
...         background_luminance=20,
...         surround='average',
...         discounting=False
...     )
... 
>>> class Color(Base): ...
... 
>>> Color.register([CAM16JMh(), CustomCAM16JMh()])
>>> Color('white').convert('cam16-jmh')
color(--cam16-jmh 100 2.2369 209.53 / 1)
>>> Color('white').convert('cam16-custom')
color(--cam16-custom 100 0.14734 209.66 / 1)

Note

It can be noted in the above example that white does not have the typical zero chroma. This is because the eye is not assumed as being fully adapted to the environment. If discounting was enabled, the eye is then assumed to be fully adapted, white would have a chroma of zero. So the settings can affect things like what is considered achromatic in the space. This is not a bug, but simply the way the model works.

Channel Aliases

Channels	Aliases
`j`	`lightness`
`m`	`colorfulness`
`h`	`hue`

Input/Output

The CAM16 JMh space is not currently supported in the CSS spec, the parsed input and string output formats use the color() function format using the custom name --cam16-jmh:

color(--cam16-jmh j m h / a)  // Color function

The string representation of the color object and the default string output use the color(--cam16-jmh j m h / a) form.

>>> Color("cam16-jmh", [59.178, 40.82, 21.153], 1)
color(--cam16-jmh 59.178 40.82 21.153 / 1)
>>> Color("cam16-jmh", [78.364, 9.6945, 28.629], 1).to_string()
'color(--cam16-jmh 78.364 9.6945 28.629)'

Registering

from coloraide import Color as Base
from coloraide.spaces.cam16_jmh import CAM16JMh

class Color(Base): ...

Color.register(CAM16JMh())