Monday, 1 March 2021

Colour Names 3

Some more colour naming experiments...

After creating the RGB-125 palette (one-word names for colours based on five levels each of red, green and blue), I limited the number of levels to 64 (4x4x4). This is similar to the EGA source palette.

The EGA palette uses the adjective "bright" to describe colours with any channel at 100% intensity. This idea is mirrored in the "vivid" modifier of the ISCC-NBS system and Color Naming System. I thought that "bright" could be confused with "light", so I chose "vivid" as the prefix for any RGB-64 colour that has maximal chroma.

RGB-64 has 39 base colour names ("amaranth", "amber", "apple", "aquamarine", "azure", "black", "blue", "bluebell", "brown", "celeste", "cerise", "cerulean", "chartreuse", "cyan", "denim", "erin", "green", "grey", "harlequin", "inchworm", "jade", "liberty", "magenta", "mauve", "milan", "mint", "olive", "orange", "orchid", "pink", "plum", "poison", "purple", "red", "spring", "tradewind", "violet", "white" and "yellow") and 3 modifiers ("dark", "light" and "vivid"). The bold names correspond to the eleven (contentious) basic colour terms.

RGB-27 is a strict subset of RGB-125 covering 3x3x3 colour points. Unfortunately, we lose "brown" and "pink" in the process.

At this point, I turned my attention to limited, hue-based colour naming schemes.

HSL-79 is a scheme based on the HSL colour space. The hue (an angle between 0 and 360 degrees) is split into 12 equal segments:

  • red
  • orange
  • yellow
  • chartreuse
  • green
  • spring
  • cyan
  • azure
  • blue
  • violet
  • magenta
  • rose
These hues can be optionally modified with prefixes:
  • deep (very low lightness)
  • dark (low lightness)
  • light (high lightness)
  • pale (very high lightness)
  • dull (low saturation)
If the saturation is high, no prefix is used. If the saturation is very low, the colour is achromatic and the lightness is used to pick from a grey scale:
  • black
  • deep grey
  • dark grey
  • grey
  • light grey
  • pale grey
  • white
These combine to form 79 unique colours: "black" and "white" do not take prefixes and "grey" cannot be "dull". I quite liked the names, though "chartreuse" and "spring" feel a little clunky.

HSV-79 is similar but based on the HSV colour space instead of HSL. I tried to parameterize the partitioning of the segment so that each contains approximately the same number of RGB (256x256x256) colour points.

HWB-91 is based on Alvy Ray Smith's HWB colour space. I can't believe I hadn't come across this before, but there you go! The twelve additional colour points (up from 79 to 91) are due to the addition of the "vivid" modify for hues. Instead of using explicit conditions to partition the space, the "whiteness" and "blackness" coordinates are used as the basis for a Euclidean "nearest neighbour" algorithm based on the following reference points (in this case, for "red"):

HWB-91 reference points for a given hue (x-axis is blackness, y-axis is whiteness)

This produces quite intuitive results. Take, for example, the web-safe colour "#FFCCFF"; "pale magenta" seems like an appropriate name:

Colour names for #FFCCFF in various schemes

The numbers in the final column are the ΔE*(2000) colour differences between "#FFCCFF" and the nearest colour from the discrete palette.

Next, I hope to look into CNS (from 1982) and/or the Artist's Color Naming System (from 1986).

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