RYB
The RYB color space is not registered in Color by default
Properties
Name: ryb
White Point: D65 / 2˚
Coordinates:
| Name | Range |
|---|---|
r | [0, 1] |
y | [0, 1] |
b | [0, 1] |
>>> Wheel(Color('ryb', [1, 0, 0]).harmony('wheel', space='ryb'))
[color(--ryb 1 0 0 / 1), color(--ryb 1 0.5 0 / 1), color(--ryb 1 1 0 / 1), color(--ryb 0.5 1 0 / 1), color(--ryb 0 1 0 / 1), color(--ryb 0 1 0.5 / 1), color(--ryb 0 1 1 / 1), color(--ryb 0 0.5 1 / 1), color(--ryb 0 0 1 / 1), color(--ryb 0.5 0 1 / 1), color(--ryb 1 0 1 / 1), color(--ryb 1 0 0.5 / 1)]
Figure 1. The RYB color wheel.
The RYB color model is a subtractive color model in which red, yellow and blue pigments or dyes are added together in various ways to reproduce different colors. RYB is the classical way of thinking about colors. While in schools it is often still taught that red, yellow, and blue are the primary colors (for pigments), modern wisdom shows that these "primaries" are not sufficient. Spaces like CMYK which use cyan, magenta and yellow can create a much wider array of colors, even red, yellow, and blue. We've also since learned that the primary colors of light (which operates in an additive color space) are red, green, and blue.
Even though in modern day electronic screens and printing we rely on color models such as RGB and CMYK, RYB still holds a special place with artists. Color harmony is often used as the model when talking about color harmonies.
There is no standard RYB color model. No standard primaries. The RYB model that ColorAide implements is based on the work of Nathan Gossett and Baoquan Chen at the University of Minnesota at Twin Cities. Their paper devised an approach of using trilinear interpolation to create a transform from RYB to sRGB. The bases of the model uses colors similar to Johannes Itten's color wheel (which we showed an example of above), but in all the literature, there are variants of the same color wheel and no precise color codes.
ColorAide implements Gossett and Chen's algorithm to convert from RYB to sRGB, but also uses an algorithm that employs Newton's method to approximates the reverse transform, something that wasn't covered in the paper.
This approach to transforming the RGB color spaces does provide more paint like mixing.
>>> Color.interpolate(['color(--ryb 0 0 1)', 'color(--ryb 0 1 0)'], space='ryb')
<coloraide.interpolate.linear.InterpolatorLinear object at 0x105ba7b60>
>>> Color.interpolate(['color(--ryb 1 0 0)', 'color(--ryb 0 1 0)'], space='ryb')
<coloraide.interpolate.linear.InterpolatorLinear object at 0x105ba76b0>
>>> Color.interpolate(['color(--ryb 1 0 1)', 'color(--ryb 0 1 0)'], space='ryb')
<coloraide.interpolate.linear.InterpolatorLinear object at 0x105ba73e0>
It should also be noted that when mixing all the colors, you do not get black, but a muddy brown, much like with paint. To be precise, the color black is not defined within this color space.
>>> Color.interpolate(['color(--ryb 0 0 0)', 'color(--ryb 1 1 1)'], space='ryb')
<coloraide.interpolate.linear.InterpolatorLinear object at 0x105ba76b0>
>>> Color.interpolate(['color(--ryb 0 0 1)', 'color(--ryb 1 1 1)'], space='ryb')
<coloraide.interpolate.linear.InterpolatorLinear object at 0x105ba7b60>
It should be noted that the RYB model does a great job at translating colors within the RYB color gamut, but translation of colors outside the gamut will have poor conversions.
RYB Biased
The RYB Biased color space is not registered in Color by default
Properties
Name: ryb-biased
White Point: D65 / 2˚
Coordinates:
| Name | Range |
|---|---|
r | [0, 1] |
y | [0, 1] |
b | [0, 1] |
>>> Wheel(Color('ryb-biased', [1, 0, 0]).harmony('wheel', space='ryb-biased'))
[color(--ryb-biased 1 0 0 / 1), color(--ryb-biased 1 0.5 0 / 1), color(--ryb-biased 1 1 0 / 1), color(--ryb-biased 0.5 1 0 / 1), color(--ryb-biased 0 1 0 / 1), color(--ryb-biased 0 1 0.5 / 1), color(--ryb-biased 0 1 1 / 1), color(--ryb-biased 0 0.5 1 / 1), color(--ryb-biased 0 0 1 / 1), color(--ryb-biased 0.5 0 1 / 1), color(--ryb-biased 1 0 1 / 1), color(--ryb-biased 1 0 0.5 / 1)]
In the Gosset and Chen paper, they also implemented an easing function that was applied to the trilinear interpolation transform. This additional easing function biases the color transform more to the corners of the cube. The idea was to better simulate how paint clumps when mixing. While we've also implemented this behavior to be true to the paper, the RYB color space does not utilize this biasing by default, but we instead provide an alternative RYB color space (ryb-biased) that implements everything fully.
Notice how the colors in the "biased" RYB are more concentrated at the corners while in the normal RYB they blend more.
>>> Color.interpolate(Color('ryb', [1, 0, 0]).harmony('wheel', space='ryb'), space='ryb')
<coloraide.interpolate.linear.InterpolatorLinear object at 0x105ba76b0>
>>> Color.interpolate(Color('ryb-biased', [1, 0, 0]).harmony('wheel', space='ryb-biased'), space='ryb-biased')
<coloraide.interpolate.linear.InterpolatorLinear object at 0x105ba73e0>
Channel Aliases
| Channels | Aliases |
|---|---|
r | red |
y | yellow |
b | blue |
Input/Output
RYB is not currently supported in the CSS spec, the parsed input and string output formats use the color() function format using the custom name --ryb. If using RYB Biased, then the custom name --ryb-biased is used.
color(--ryb r y b / a) // Color function
color(--ryb-biased r y b / a) // Color function
The string representation of the color object and the default string output use the color(--ryb r y b / a) form or color(--ryb-biased r y b / a) for the biased variant.
>>> Color("ryb", [1, 0, 0])
color(--ryb 1 0 0 / 1)
>>> Color("ryb", [0.70588, 1, 0]).to_string()
'color(--ryb 0.70588 1 0)'
>>> Color("ryb", [0, 1, 0])
color(--ryb 0 1 0 / 1)
>>> Color("ryb", [0.37952, 1.289, 1.014]).to_string()
'color(--ryb 0.36388 1 0.93018)'
Registering
Either RYB, RYB Biased, or both can be registered.
from coloraide import Color as Base
from coloraide.spaces.ryb import RYB, RYBBiased
class Color(Base): ...
Color.register([RYB(), RYBBiased()])