Munsell Colorspace (Colorspaces IX)

While the RGB and its transformed colorspaces are useful for computer graphics and video compression, there are other colorspaces that deal with “real life” materials, like ink and paint. Albert Henry Munsell (1858–1918), a painter, proposed such a system.

Unlike RGB and its friends, the Munsell colorspace isn’t based on mixing three primaries, but rather on hue (tint), value (brightness) and chroma (density of color, or saturation), and colors are arranged on a color wheel, but unlike the usual three/six primary color wheel, Munsell’s has 5 primary colors [1].

Munsell’s primary colors are:

  • R, Red, at 0°,
  • Y, Yellow, at 72°,
  • G, Green, at 144°,
  • B, Blue, at 216°,
  • P, Purple, at 288°.

With intermediate colors

  • YR, Yellow-Red (orange?), at 36°,
  • GY, Greenish-Yellow, at 108°,
  • BG, Blue-Green (cyan?), at 180°,
  • PB, Purplish-Blue, at 252°,
  • RP, Reddish-Purple, at 324°.

In this system, a color is first indexed by one of the colors codes, scaled by a number between 0 (pure color) and 10 (10 being the next color). 7.5YR would be between YR and Y, 1/4 YR and 3/4 Y. Value, or brightness varies from 1 (very dark) to 9 (very bright). Chroma, or saturation seems to vary between 0 (gray) and 20 (pure color). The central spoke is the black-white axis.

In the available data, not all colors are actually mappable to RGB. Some aren’t even mappable to CIÉ XYZ space. In the above animated render, only the RGBable colors are shown.

* *

Munsell, [1, p. 49], claims that the three/six sided colors wheels have “false color balance”: the colors are equally spaced on the wheel, but not perceptually. Moreover, the usual color-complement color pairs are wrong, as “tested by the mixture of colored lights”. That’s a [reference needed] moment.

[1] Albert Henry Munsell — A Color Notation: an Illustrated System Defining All Colors and Their Relations by Measured Scales of Hue, Value, and Chroma — Munsell Color Company (1919) (online).

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