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vnIIc
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Floyd-Steinberg error diffusion dither

This commit is contained in:
Joshua Bell 2018-10-27 17:06:38 -07:00
parent e0a7a08915
commit 8ef502b973
1 changed files with 54 additions and 22 deletions
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76
index.html
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@ -53,7 +53,7 @@ const palette = [
}
})();
function distance(r1,g1,b1,r2,b2,g2) {
function distance(r1,g1,b1,r2,g2,b2) {
const dr = r1 - r2;
const dg = g1 - g2;
const db = b1 - b2;
@ -68,31 +68,63 @@ function quantize(imagedata) {
hash[rgb] = i;
}
// Nearest Neighbor
for (let i = 0; i < imagedata.data.length; i += 4) {
const r = imagedata.data[i];
const g = imagedata.data[i+1];
const b = imagedata.data[i+2];
// Floyd-Steinberg
function offset(x, y) {
return 4 * (x + y * imagedata.width);
}
const rgb = (r << 16) | (g << 8) | b;
let index = hash[rgb];
if (index === undefined) {
let dist;
for (let p = 0; p < palette.length; ++p) {
const entry = palette[p];
const d = distance(r,g,b, entry[0], entry[1], entry[2]);
if (dist === undefined || d < dist) {
dist = d;
index = p;
function err(x, y, er, eg, eb) {
if (x < 0 || x >= imagedata.width || y < 0 || y >= imagedata.height)
return;
const i = offset(x, y);
const data = imagedata.data;
data[i + 0] += er;
data[i + 1] += eg;
data[i + 2] += eb;
}
const data = imagedata.data;
for (let y = 0; y < imagedata.height; ++y) {
for (let x = 0; x < imagedata.width; ++x) {
const i = offset(x, y);
const r = data[i];
const g = data[i+1];
const b = data[i+2];
// Find closest in palette.
const rgb = (r << 16) | (g << 8) | b;
let index = hash[rgb];
if (index === undefined) {
let dist;
for (let p = 0; p < palette.length; ++p) {
const entry = palette[p];
const d = distance(r,g,b, entry[0], entry[1], entry[2]);
if (dist === undefined || d < dist) {
dist = d;
index = p;
}
}
hash[rgb] = index;
}
hash[rgb] = index;
}
const pi = palette[index];
const pi = palette[index];
imagedata.data[i] = pi[0];
imagedata.data[i+1] = pi[1];
imagedata.data[i+2] = pi[2];
// Calculate error
const err_r = data[i] - pi[0];
const err_g = data[i+1] - pi[1];
const err_b = data[i+2] - pi[2];
// Update pixel
data[i] = pi[0];
data[i+1] = pi[1];
data[i+2] = pi[2];
// Distribute error
err(x + 1, y, err_r * 7/16, err_g * 7/16, err_b * 7/16);
err(x - 1, y + 1, err_r * 3/16, err_g * 3/16, err_b * 3/16);
err(x, y + 1, err_r * 5/16, err_g * 5/16, err_b * 5/16);
err(x + 1, y + 1, err_r * 1/16, err_g * 1/16, err_b * 1/16);
}
}
}