The HSL rainbow (all hues at 100% saturation and 50% lightness) has highly variable luminance: we perceive some parts of the rainbow, such as between yellow and cyan, as significantly brighter than other parts of the rainbow. This, along with a lack of perceptual uniformity, makes the rainbow color scale unsuitable for visualization. Use the Lab or HCL color space instead.
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Rainbow Luminance
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| license: gpl-3.0 |
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| <!DOCTYPE html> | |
| <meta charset="utf-8"> | |
| <style> | |
| body { | |
| font-family: "Helvetica Neue", Helvetica, Arial, sans-serif; | |
| } | |
| .space { | |
| position: absolute; | |
| } | |
| .space div { | |
| position: absolute; | |
| top: 0; | |
| left: 20px; | |
| } | |
| </style> | |
| <body> | |
| <script src="//d3js.org/d3.v3.min.js"></script> | |
| <script> | |
| var spaces = [ | |
| { | |
| name: "Rainbow (HSL)", | |
| color: function(t) { | |
| return d3.hsl(t * 360, 1, .5); | |
| } | |
| }, | |
| { | |
| name: "Luminance", | |
| color: function(t) { | |
| var c = d3.hcl(d3.hsl(t * 360, 1, .5)); | |
| c.c = 0; | |
| return c; | |
| } | |
| } | |
| ]; | |
| var y = d3.scale.ordinal() | |
| .domain(spaces.map(function(d) { return d.name; })) | |
| .rangeRoundBands([0, 500], .1); | |
| var margin = y.range()[0], | |
| width = 960 - margin - margin, | |
| height = y.rangeBand(); | |
| var space = d3.select("body").selectAll(".space") | |
| .data(spaces) | |
| .enter().append("div") | |
| .attr("class", "space") | |
| .style("width", width + "px") | |
| .style("height", height + "px") | |
| .style("left", margin + "px") | |
| .style("top", function(d) { return y(d.name) + "px"; }); | |
| var canvas = space.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)); | |
| image.data[++j] = c.r; | |
| image.data[++j] = c.g; | |
| image.data[++j] = c.b; | |
| image.data[++j] = 255; | |
| } | |
| context.putImageData(image, 0, 0); | |
| }); | |
| space.append("div") | |
| .style("line-height", height + "px") | |
| .text(function(d) { return d.name; }); | |
| </script> |
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