Adams chromatic valence colour spaces

They are a class of colour spaces suggested by Elliot Quincy Adams. They are of two types: Chromatic value spaces and Chromatic valence spaces.

Two important chromatic value/valence spaces are CIELUV and Hunter Lab.

Chromatic value/valence spaces are notable for incorporating the Opponent Processes model and the empirically determined $2^{1/2}$ factor in the red/green vs blue/yellow chromaticity components (such as in CIELAB).

Types

• Chromatic value spaces
  • In 1942, Adams suggested chromatic value colour spaces. Chromatic values, or chromance refers to the intensity of the opponent process responses and is derived from Adams’ theory of olour vision.
  • A chromatic value space consists of three components
    • $V_Y$, the Munsell-Sloan-Godlove value function $V_Y^2=1.4742Y-0.004743Y^2$
    • $V_X-V_Y$, the red-green chromaticity dimension
    • $V_Z-V_Y$, the blue-yellow chromaticity dimension
  • A chromatic value diagram is a plot of $V_X-V_Y$ (horizontal axis) vs $0.4(V_Z-V_Y)$ (vertical axis). The $2^{1/2}$ scale factor is intended to make the radial distance from the White Point correlate with the Munesell chroma along any one hue radius (i.e. to make the diagram perceptually uniform).
  • For achromatic surfaces $(y_n/x_n)X=Y=(y_n/x_n)Z$, and hence $V_X-V_Y=0,V_Z-V_Y=0$. In other words, the White Point is at the origin
  • Constant differences in the chroma dimension did not appear different by a corresponding amount, so Adamns proposed a new class of spaces named chromatic valence.
• Chromatic valence spaces
  • These spaces have nearly equal radia distances for equal changes in Munsell chroma.
  • They incorporate two relatively perceptually uniform elements: a chromaticity scale and a lightness scale.
  • The Lightness scale is determined using the Newhall-Nickerson-Judd value function, and forms one axis of the colour space.
  • The remaining two axes are formed by multiplying the two uniform chromaticity coordinates by the lightness, $V_J$
  • $\frac{X/x_n}{Y/y_n}-1=\frac{X/x_n-Y/y_n}{Y/y_n}$ $\frac{X/x_n}{Y/y_n}-1=\frac{X/x_n-Y/y_n}{Y/y_n}$
    • This is essentially what Hunter used in his Lab colour space.
    • As with chromatic value, these functions are plotted with a scale factor of $2^{1/2}$ to give nearly equal radial distance for equal changes in Munsell chroma.

Colour Difference

Adam’s colour spaces rely on the Munsell value.

Defining chromatic valence components $W_X=(\frac{x/x_n}{y/y_n}-1)V_J$ and $W_Z=(\frac{z/z_n}{y/y_n}-1)V_J$ we can determine the Colour Difference $\Delta E=\sqrt{(0.4\Delta V_J{)}^2+(\Delta W_X{)}^2+(0.4\Delta W_Z{)}^2}$

where $V_J$ is the Newhall-Nickerson-Judd-value function and the 0.4 factor is incorporated to better make the differences in $W_X$ and $W_Y$ correspond to one another.

In chromatic value colour spaces, the chromaticity components are $W_X=(V_X-V_Y)$ and $W_Z=V_Z-V_Y$. The difference is: $\Delta E=\sqrt{(0.23\Delta V_Y{)}^2+(\Delta W_X{)}^2+(0.4\Delta W_Z{)}^2}$

where $V_Y$, the Munsell-Sloan-Godlove value function is applied to the tristimulus value indicated in the subscript.