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.