I was intrigued to find a referenc to the colour theory of Johannes Itten (b. 1888), as it is rare to find the RYB colour model used in computer based colour theory. Authors Tom De Smedt and Frederick De Blesser agree some rough adjustments to the colour intervals based on the HSB (hue, saturation and brightness) colour model. HSB is similar to HSV (hue, saturation and value, and are 3D models.
The first 3D colour model is often attributed to Prof. A. H. Munsell (b. 1858). See ‘A Color Notation’ (1915) and ‘Atlas of the Munsell Color System’ (1915).
Unlike RYB which is a tertiary/duo decimal system (and other colour models), Munsell, is a decimal based system, which organises colour in perceptually equal intervals based on hue, value and chroma.
The 1943, Munsell renotation defines the Munsell colour system in CIE (Commission internationale de l’éclairage) coordinates. This is the current standard, and it reduces the number of hue steps from 100 to 40. However, there remain a total of 2745 colours represented. Of these, 1221 lie outside the sRGB gamut, and cannot be represented in any sRGB based colour system.
See also https://ugajin.wordpress.com/2014/02/10/on-munsell/.
The following is a selected extract from the Python __init__.py library file
def rotate_ryb(self, angle=180):
“”” Returns a color rotated on the artistic RYB color wheel.
An artistic color wheel has slightly different opposites
(e.g. purple-yellow instead of purple-lime).
It is mathematically incorrect but generally assumed
to provide better complementary colors.
http://en.wikipedia.org/wiki/RYB_color_model
“””
# Approximation of Itten’s RYB color wheel.
# In HSB, colors hues range from 0-360.
# However, on the artistic color wheel these are not evenly distributed.
# The second tuple value contains the actual distribution.
wheel = [( 0, 0), ( 15, 8),
( 30, 17), ( 45, 26),
( 60, 34), ( 75, 41),
( 90, 48), (105, 54),
(120, 60), (135, 81),
(150, 103), (165, 123),
(180, 138), (195, 155),
(210, 171), (225, 187),
(240, 204), (255, 219),
(270, 234), (285, 251),
(300, 267), (315, 282),
(330, 298), (345, 329),
(360, 0 )
]
ugajin 