graphic = {
replay;
const quads = new TinyQueue([new Quad(0, 0, width, width)], (a, b) => b.score - a.score);
const context = DOM.context2d(width, width);
context.canvas.style.width = "100%";
for (let i = 0; true; ++i) {
const q = quads.pop();
if (q === undefined || q.score < 50) break;
mutable score = q.score;
for (const s of q.split()) {
if (q.w >= 4) quads.push(s);
context.fillStyle = colorFromWidth(Math.sqrt(s.w / 1024 * 4) * 255); // sqrt grayscale
context.fillRect(s.x, s.y, s.w, s.h);
context.strokeStyle = s.color;
context.strokeRect(s.x, s.y, s.w, s.h);
}
if (i % 15 === 0) yield context.canvas;
}
}
class Quad {
constructor(x, y, w, h) {
const [r, g, b, error] = colorFromHistogram(computeHistogram(x, y, w, h));
this.x = x, this.y = y, this.w = w, this.h = h;
this.color = `#${(0x1000000 + (r << 16) + (g << 8) + b).toString(16).substring(1)}`;
this.score = error * Math.pow(w * h, area_power);
}
split() {
const dx = this.w / 2, x1 = this.x, x2 = this.x + dx;
const dy = this.h / 2, y1 = this.y, y2 = this.y + dy;
return [
new Quad(x1, y1, dx, dy),
new Quad(x2, y1, dx, dy),
new Quad(x1, y2, dx, dy),
new Quad(x2, y2, dx, dy)
];
}
}
function computeHistogram(x, y, w, h) {
const {data} = imageContext.getImageData(x, y, w, h);
const histogram = new Uint32Array(1024);
for (let i = 0, n = data.length; i < n; i += 4) {
++histogram[0 * 256 + data[i + 0]];
++histogram[1 * 256 + data[i + 1]];
++histogram[2 * 256 + data[i + 2]];
++histogram[3 * 256 + data[i + 3]];
}
return histogram;
}
function weightedAverage(histogram) {
let total = 0;
let value = 0;
for (let i = 0; i < 256; ++i) total += histogram[i], value += histogram[i] * i;
value /= total;
let error = 0;
for (let i = 0; i < 256; ++i) error += (value - i) ** 2 * histogram[i];
return [value, Math.sqrt(error / total)];
}
function colorFromHistogram(histogram) {
const [r, re] = weightedAverage(histogram.subarray(0, 256));
const [g, ge] = weightedAverage(histogram.subarray(256, 512));
const [b, be] = weightedAverage(histogram.subarray(512, 768));
return [
Math.round(r),
Math.round(g),
Math.round(b),
re * 0.2989 + ge * 0.5870 + be * 0.1140
];
}
One platform to build and deploy the best data apps
Experiment and prototype by building visualizations in live JavaScript notebooks. Collaborate with your team and decide which concepts to build out.
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