From 2c943419ce914f2b11ec8ed0e07796953bf718cd Mon Sep 17 00:00:00 2001
From: Brion Vibber <brion@pobox.com>
Date: Mon, 20 Mar 2023 20:36:12 -0700
Subject: [PATCH] woo

---
 dither-image.js | 157 ++++++------------------------------------------
 1 file changed, 19 insertions(+), 138 deletions(-)

diff --git a/dither-image.js b/dither-image.js
index e2927dd..49d7ef4 100644
--- a/dither-image.js
+++ b/dither-image.js
@@ -98,10 +98,6 @@ class RGB {
         );
     }
 
-    add(other) {
-        return RGB.add(this, other);
-    }
-
     difference(other) {
         return new RGB(
             this.r - other.r,
@@ -110,6 +106,14 @@ class RGB {
         );
     }
 
+    multiply(scalar) {
+        return new RGB(
+            this.r * scalar,
+            this.g * scalar,
+            this.b * scalar,
+        );
+    }
+
     divide(scalar) {
         return new RGB(
             this.r / scalar,
@@ -472,15 +476,12 @@ function decimate(input, palette, n, inputError, y) {
             output[x] = pick;
             popularity[pick]++;
 
-            let shares = 8;
-            let single = nextError.divide(shares);
-            let double = nextError.divide(shares / 2);
-            error.cur[x + 1]?.inc(double);
-            error.cur[x + 2]?.inc(single);
+            let share = (n) => nextError.multiply(n / 16);
 
-            error.next[x - 1]?.inc(single);
-            error.next[x]?.inc(double);
-            error.next[x + 1]?.inc(double);
+            error.cur[x + 1]?.inc(share(7));
+            error.next[x - 1]?.inc(share(3));
+            error.next[x    ]?.inc(share(5));
+            error.next[x + 1]?.inc(share(1));
 
             let mag = nextError.magnitude();
             fitness[x] = maxDist / mag;
@@ -533,129 +534,6 @@ function decimate(input, palette, n, inputError, y) {
         keepers[i & 0xfe] = 1; // drop that 0 luminance bit!
     }
 
-    // this takes the top hues, and uses the brightest of each hue
-    // needs tuning
-    /*
-    // first, dither to the total atari palette
-    while (decimated.length > n) {
-        let {popularity} = dither(decimated);
-        let hues = zeros(16);
-        let lumas = zeros(16);
-        for (let i = 0; i < decimated.length; i++) {
-            let color = decimated[i];
-            let hue = color >> 4;
-            let luma = color & 0xe;
-            hues[hue] += popularity[i];
-            if (luma > lumas[hue]) {
-                lumas[hue] = luma;
-            }
-        }
-
-        let a = hues;
-        a = a.map((count, hue) => { return {count, hue} });
-        a = a.sort((a, b) => b.count - a.count);
-        a = a.map(({hue}) => hue);
-        a = a.filter((color) => !keepers[color]);
-        //a = a.slice(0, n - reserved.length);
-        a = a.slice(0, decimated.length - 1 - reserved.length);
-        a = a.map((hue) => (hue << 4) | lumas[hue]);
-        a = a.sort((a, b) => a - b);
-
-        decimated = reserved.concat(a);
-    }
-    console.log('end', decimated);
-    */
-
-    // popularity? not really working right
-    // first, dither to the total atari palette
-    /*
-    while (decimated.length > n) {
-        //console.log(y);
-
-        let {popularity, fitness, output} = dither(decimated);
-        let pops = [];
-        let fits = [];
-        pops.fill(0, 0, 256);
-        fits.fill(0, 0, 256);
-        for (let i = 0; i < decimated.length; i++) {
-            let c = decimated[i];
-            pops[c] = popularity[i];
-            for (let x = 0; x < fitness.length; x++) {
-                if (output[x] === i) {
-                    fits[c] += fitness[x];
-                }
-            }
-        }
-        let metric = (c) => {
-            let rgb = atariRGB[c];
-            let max = Math.max(rgb.r, rgb.g, rgb.b);
-            let fit = fits[c];
-            let pop = pops[c];
-            return pop;
-        }
-
-        let a = decimated.slice();
-        // temporarily strip the reserved items
-        a = a.filter((color) => !keepers[color]);
-        a = a.filter((color) => popularity[color]);
-        a.sort((a, b) => {
-            return metric(b) - metric(a);
-        });
-        console.log(a);
-        a = reserved.concat(a);
-        decimated = a.slice(0, n);
-        //decimated = a.slice(0, decimated.length - 1);
-        //console.log(decimated);
-    }
-    */
-    //console.log('end', decimated);
-
-    // old algo
-    /*
-    while (decimated.length > n) {
-        let {popularity, fitness, output} = dither(decimated);
-
-        // Try dropping least used color on each iteration
-        let least = Infinity;
-        let pick = -1;
-        for (let i = 1; i < decimated.length; i++) {
-
-            //let coolFactor = popularity[i];
-
-            let coolFactor = 0;
-            if (popularity[i]) {
-                for (let x = 0; x < width; x++) {
-                    if (output[x] == i) {
-                        // Scale up the scoring for close matches to prioritize
-                        // color accuracy over raw linear usage.
-                        //coolFactor += (fitness[x] ** 2);
-                        coolFactor += (fitness[x] ** 4);
-                    }
-                }
-            }
-            if (coolFactor < least) {
-                pick = i;
-                least = coolFactor;
-            }
-            decimated = decimated.filter((color, i) => {
-                if (i == 0) {
-                    return true;
-                }
-                if (i == pick) {
-                    return false;
-                }
-                // Also drop any non-black unused colors to save trouble.
-                // However -- this may change dither results.
-                // Try this with/without later.
-                if (popularity[i] == 0) {
-                    return false;
-                }
-                return true;
-            });
-        }
-    }
-    */
-
     // Median cut!
     // https://en.wikipedia.org/wiki/Median_cut
     //let buckets = [input.slice()];
@@ -694,13 +572,16 @@ function decimate(input, palette, n, inputError, y) {
     }
     decimated = buckets.map((bucket) => {
         // Average the RGB colors in this chunk
-        let rgb = bucket
-            .reduce((acc, rgb) => acc.inc(rgb), new RGB(0, 0, 0))
-            .divide(bucket.length);
+        //let rgb = bucket
+        //    .reduce((acc, rgb) => acc.inc(rgb), new RGB(0, 0, 0))
+        //    .divide(bucket.length);
 
         // Take the brightest color in the bucket
         //let rgb = bucket[bucket.length - 1];
 
+        // Take the median color in the bucket
+        let rgb = bucket[bucket.length >> 1];
+
         // And map into the Atari palette
         let dists = palette.map((   i) => rgb.difference(atariRGB[i]).magnitude());
         let closest = Math.min(...dists);