From 1d3712be5c89e3528d58da4d29514cbce7d9d030 Mon Sep 17 00:00:00 2001
From: Brion Vibber <brion@pobox.com>
Date: Fri, 24 Mar 2023 00:23:59 -0700
Subject: [PATCH] wip

---
 dither-image.js | 43 ++++++++++++++-----------------------------
 1 file changed, 14 insertions(+), 29 deletions(-)

diff --git a/dither-image.js b/dither-image.js
index f804df8..ee313d0 100644
--- a/dither-image.js
+++ b/dither-image.js
@@ -134,13 +134,23 @@ class RGB {
             this.b * this.b;
     }
 
+    sum() {
+        return this.r + this.g + this.b;
+    }
+
+    lumaScale() {
+        return new RGB(
+            this.r * 0.299,
+            this.g * 0.586,
+            this.b * 0.114
+        );
+    }
+
     luma() {
-        return this.r * 0.299 + this.g * 0.587 + this.b * 0.114;
+        return this.lumaScale().sum();
     }
 }
 
-const maxDist = (new RGB(255, 255, 255)).magnitude();
-
 // snarfed from https://lospec.com/palette-list/atari-8-bit-family-gtia
 // which was calculated with Retrospecs App's Atari 800 emulator
 let atariRGB = [
@@ -414,19 +424,6 @@ let atariRGB = [
  * @returns {{output: number[], palette: number[], error: RGB[]}}
  */
 function decimate(input, palette, n) {
-    // to brute-force, the possible palettes are:
-    // 255 * 254 * 253 = 16,386,810
-    //
-    // we could brute force it but that's a lot :D
-    // but can do some bisection :D
-    //
-    // need a fitness metric.
-    // each pixel in the dithered line gives a distance
-    // sum/average them? median? maximum?
-    // summing evens out the ups/downs from dithering
-    // but doesn't distinguish between two close and two distant options
-    // consider median, 90th-percentile, and max of abs(distance)
-    // consider doing the distance for each channel?
 
     let width = input.length;
 
@@ -440,7 +437,6 @@ function decimate(input, palette, n) {
 
     // Apply dithering with given palette and collect color usage stats
     let dither = (palette) => {
-        let fitness = zeroes(width);
         let error = {
             cur: [],
             next: [],
@@ -467,7 +463,7 @@ function decimate(input, palette, n) {
 
             for (let i = 0; i < palette.length; i++) {
                 let diff = rgb.difference(atariRGB[palette[i]]);
-                let dist = diff.magnitude2();
+                let dist = diff.magnitude();
                 if (dist < shortest) {
                     nextError = diff;
                     shortest = dist;
@@ -484,21 +480,10 @@ function decimate(input, palette, n) {
             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;
-            // 442 is the 3d distance across the rgb cube
-            //fitness[x] = 442 - (nextError.magnitude());
-            //fitness[x] = 442 / (442 - nextError.magnitude());
-            fitness[x] = 255 / (256 - Math.max(0, nextError.r, nextError.g, nextError.b));
-
-            let mag2 = nextError.magnitude2();
-            distance2 += mag2;
         }
         return {
             output,
             palette,
-            fitness,
             distance2,
             popularity,
             error: error.next