More examples of the d3.interpolateCubehelix plugin, replicating four Python cubehelix examples. In the last two examples, a polylinear scale creates a diverging cubehelix color ramp, and an approximate recreation of Matteo Niccoli’s perceptual rainbow.
Cubehelix II
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license: gpl-3.0 |
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(function() { | |
var radians = Math.PI / 180; | |
d3.scale.cubehelix = function() { | |
return d3.scale.linear() | |
.range([d3.hsl(300, .5, 0), d3.hsl(-240, .5, 1)]) | |
.interpolate(d3.interpolateCubehelix); | |
}; | |
d3.interpolateCubehelix = d3_interpolateCubehelix(1); | |
d3.interpolateCubehelix.gamma = d3_interpolateCubehelix; | |
function d3_interpolateCubehelix(γ) { | |
return function(a, b) { | |
a = d3.hsl(a); | |
b = d3.hsl(b); | |
var ah = (a.h + 120) * radians, | |
bh = (b.h + 120) * radians - ah, | |
as = a.s, | |
bs = b.s - as, | |
al = a.l, | |
bl = b.l - al; | |
if (isNaN(bs)) bs = 0, as = isNaN(as) ? b.s : as; | |
if (isNaN(bh)) bh = 0, ah = isNaN(ah) ? b.h : ah; | |
return function(t) { | |
var h = ah + bh * t, | |
l = Math.pow(al + bl * t, γ), | |
a = (as + bs * t) * l * (1 - l); | |
return "#" | |
+ hex(l + a * (-0.14861 * Math.cos(h) + 1.78277 * Math.sin(h))) | |
+ hex(l + a * (-0.29227 * Math.cos(h) - 0.90649 * Math.sin(h))) | |
+ hex(l + a * (+1.97294 * Math.cos(h))); | |
}; | |
}; | |
} | |
function hex(v) { | |
var s = (v = v <= 0 ? 0 : v >= 1 ? 255 : v * 255 | 0).toString(16); | |
return v < 0x10 ? "0" + s : s; | |
} | |
})(); |
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<!DOCTYPE html> | |
<meta charset="utf-8"> | |
<style> | |
body { | |
font-family: "Helvetica Neue", Helvetica, Arial, sans-serif; | |
} | |
.ramp { | |
position: absolute; | |
} | |
.ramp div { | |
position: absolute; | |
top: 0; | |
right: 20px; | |
} | |
.ramp[name='Reversed'] div { | |
color: #fff; | |
} | |
</style> | |
<body> | |
<script src="//d3js.org/d3.v3.min.js"></script> | |
<script src="cubehelix.js"></script> | |
<script> | |
var ramps = [ | |
{ | |
name: "Default", | |
color: d3.scale.cubehelix() | |
}, | |
{ | |
name: "Reversed", | |
color: d3.scale.cubehelix() | |
.domain([1, 0]) | |
}, | |
{ | |
name: "Hue [276°, 96°]", | |
color: d3.scale.cubehelix() | |
.range([d3.hsl(276, .6, 0), d3.hsl(96, .6, 1)]) | |
}, | |
{ | |
name: "Hue [-120°, 60°]", | |
color: d3.scale.cubehelix() | |
.range([d3.hsl(-120, .6, 0), d3.hsl(60, .6, 1)]) | |
}, | |
{ | |
name: "Hue [-40°, 60°, 160]", | |
color: d3.scale.cubehelix() | |
.domain([0, .5, 1]) | |
.range([d3.hsl(-40, .6, .3), d3.hsl(60, .6, 1), d3.hsl(160, .6, .3)]) | |
}, | |
{ | |
name: "Rainbow", | |
color: d3.scale.cubehelix() | |
.range([d3.hsl(270, .75, .35), d3.hsl(70, 1.5, .8)]) | |
} | |
]; | |
var y = d3.scale.ordinal() | |
.domain(ramps.map(function(d) { return d.name; })) | |
.rangeRoundBands([0, 500], .1); | |
var margin = y.range()[0], | |
width = 960 - margin - margin, | |
height = y.rangeBand(); | |
var ramp = d3.select("body").selectAll(".ramp") | |
.data(ramps) | |
.enter().append("div") | |
.attr("class", "ramp") | |
.attr("name", function(d) { return d.name; }) | |
.style("width", width + "px") | |
.style("height", height + "px") | |
.style("left", margin + "px") | |
.style("top", function(d) { return y(d.name) + "px"; }); | |
var canvas = ramp.append("canvas") | |
.attr("width", width) | |
.attr("height", 1) | |
.style("width", width + "px") | |
.style("height", height + "px") | |
.each(function(d) { | |
var context = this.getContext("2d"), | |
image = context.createImageData(width, 1); | |
for (var i = 0, j = -1, c; i < width; ++i) { | |
c = d3.rgb(d.color(i / (width - 1))); | |
image.data[++j] = c.r; | |
image.data[++j] = c.g; | |
image.data[++j] = c.b; | |
image.data[++j] = 255; | |
} | |
context.putImageData(image, 0, 0); | |
}); | |
ramp.append("div") | |
.style("line-height", height + "px") | |
.text(function(d) { return d.name; }); | |
</script> |
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