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• css hwb parser
• hwb_to_rgb converter
• rgb_to_hwb converter

...in both linear and spline interpolators. Also need to check for correct hue normalization before and after the process.

• lch css parser
• lch_to_rgb converter
• rgb_to_lch converter

With closed and open variants, like in D3. the closed version can be useful for radial sliders for hue.

L = 0.2126 * R + 0.7152 * G + 0.0722 * B in LRGB space.

contrast = (L1 + 0.05) / (L2 + 0.05) in the WGAG spec.

Arguments for enumerable

• Extending a color with { ...color } maintains the flags.

Arguments against enumerable

• Cleaner output in the console and tests. (although tests will need to check the flags separately, for better coverage)
• May be that extending a color with { ...color } will result in inaccurate flags.

• lab css parser
• lab_to_rgb converter
• rgb_to_lab converter

Use a v-p tree to index() a set of colors based on a specific difference() to enable queries of the type: what are the closest colors in the index to a given color?

Reference: http://pnylab.com/papers/vptree/main.html

Example JS implementation: https://github.com/fpirsch/vptree.js

https://mycarta.wordpress.com/2013/02/21/perceptual-rainbow-palette-the-method/
https://bl.ocks.org/mbostock/310c99e53880faec2434

• gray css parser
• gray_to_rgb converter
• rgb_to_gray converter

For linear interpolation:

• Bring back short vs. long hue interpolation
• Check hue normalization throughout the hue() method

For spline interpolation:

• Add closed version
• How to spline-interpolate alpha?
• How to spline-interpolate short vs long hue?

• need to check that performance was not degraded with current developments...

because the index will be passed as the second parameter

e.g. red to blue https://beta.observablehq.com/@danburzo/culori-scales-test

https://www.vis4.net/blog/2011/12/avoid-equidistant-hsv-colors/#picker

interpolate(color_array, mode = 'rgb') returns an interpolator function that takes an argument [0, 1].

• cubehelix_to_rgb converter
• rgb_to_cubehelix converter

Regardless of the various formats the colors come in, they ultimately reflect a RGB(A) value, so it makes sense to keep the internal format as R, G, B, A (floating-point values): in -> RGBA -> out

However, for the purposes of color scales, one might have three colors defined:

H - 120, S, L, A
H, S, L, A
H + 120, S, L, A

In which case H could go beyond [0, 360] and we need to store the original value to properly interpolate.

Simple, Euclidean distance + read up on these: http://bl.ocks.org/mourner/8a3968f74da743a754af

• b-spline
• natural spline

Reading material:

• https://www.mathworks.com/help/curvefit/cscvn.html
• G. Koloskov, "Closed natural splines: An effective solution"
• E.T.Y. Lee, "Choosing nodes in parametric curve interpolation"

blue, green, 8 colors: https://beta.observablehq.com/@danburzo/culori-scales-test

https://bids.github.io/colormap/
https://github.com/BIDS/colormap/blob/master/colormaps.py

swatches(interpolator, no_of_colors) to generate color scales.

scale(colors, mode, no_of_colors) can be implemented as swatches(interpolate(colors, mode), no_of_colors).

Like css but outputs to the formats defined in Color Module Level 4.

https://github.com/d3/d3-cam16
https://github.com/connorgr/d3-cam02
http://gramaz.io/d3-cam02/

don't allow mix of percentages and numbers.

e.g. https://github.com/acterhd/hcg-color

Currently, parsers cannot be added - let's have string parsing match CSS Color Level 4.
Converters can be created, but they can't be registered, so we need an API for that.

• hsi_to_rgb converter
• rgb_to_hsi converter

http://www.hsluv.org/