From 6af5d43943dfe4823fe3373938060659f09fe0ec Mon Sep 17 00:00:00 2001
From: Brion Vibber <brion@pobox.com>
Date: Sun, 19 Mar 2023 16:33:12 -0700
Subject: [PATCH] wip

---
 dither-image.js | 65 +++++++++++++++++++++++++++++--------------------
 1 file changed, 39 insertions(+), 26 deletions(-)

diff --git a/dither-image.js b/dither-image.js
index fc523e1..0157f2b 100644
--- a/dither-image.js
+++ b/dither-image.js
@@ -386,9 +386,10 @@ let atariRGB = [
  * @param {number[]} palette - current working palette, as Atari 8-bit color values (low nybble luminance, high nybble hue)
  * @param {number} n - target color count
  * @param {RGB[]} inputError
+ * @param {number} y
  * @returns {{output: Uint8Array, palette: number[], error: RGB[]}}
  */
-function decimate(input, palette, n, inputError) {
+function decimate(input, palette, n, inputError, y) {
     // to brute-force, the possible palettes are:
     // 255 * 254 * 253 = 16,386,810
     //
@@ -408,7 +409,7 @@ function decimate(input, palette, n, inputError) {
     let inputPixel = (x, error) => {
         let rgb = input[x].clone();
         if (error) {
-            rgb.add(error.cur[x]);
+            rgb.inc(error.cur[x]);
         }
         if (inputError) {
             rgb.inc(inputError[x]);
@@ -499,39 +500,52 @@ function decimate(input, palette, n, inputError) {
     //reserved = [0, 5, 10, 15]; // grayscale
     //reserved = [0, 0x48, 0x78, 15]; // vaporwave
     //reserved = [0, 0x3c, 0x78, 15]; // red/blue/white
+    /*
+    if (( y & 1 ) === 0) {
+        reserved = [0, 0x3c, 0x1a, 15]; // red/yellow/white
+    } else {
+        reserved = [0, 0x76, 0x9a, 15]; // blue/cyan/white
+    }
+    */
 
     let keepers = new Uint8Array(256);
     for (let i of reserved) {
         keepers[i & 0xfe] = 1; // drop that 0 luminance bit!
     }
 
+    let zeros = (n) => {
+        let arr = [];
+        for (let i = 0; i < n; i++) {
+            arr.push(0);
+        }
+        return arr;
+    };
+
+    // first, dither to the total atari palette
     while (decimated.length > n) {
-        // Try dithering to every possible subset
-        // See which has the worst overall fit and drop it
-        let farthest = -1;
-        let worstIndex = -1;
+        let {popularity} = dither(decimated);
+        let hues = zeros(16);
+        let lumas = zeros(16);
         for (let i = 0; i < decimated.length; i++) {
             let color = decimated[i];
-            if (keepers[color]) {
-                continue;
-            }
-
-            let shorter = decimated.filter((x) => x != i);
-            let {distance2} = dither(shorter);
-
-            if (distance2 >= farthest) {
-                farthest = distance2;
-                worstIndex = i;
+            let hue = color >> 4;
+            let luma = color & 0xe;
+            hues[hue] += popularity[i];
+            if (luma > lumas[hue]) {
+                lumas[hue] = luma;
             }
         }
-        console.log(`worstIndex ${worstIndex} farthest ${farthest}`);
-        let foo = decimated.length;
-        decimated.splice(worstIndex, 1);
-        //console.log(decimated.length);
-        if (decimated.length == foo) {
-            throw new Error('this should not happen');
-        }
-        //console.log('n ', decimated);
+
+        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.map((hue) => (hue << 4) | lumas[hue]);
+        a = a.sort((a, b) => a - b);
+
+        decimated = reserved.concat(a);
     }
     console.log('end', decimated);
 
@@ -626,10 +640,9 @@ async function convert(source, nbits) {
 
     let lines = [];
     for (let y = 0; y < height; y++) {
-        console.log(`y ${y}`);
         let error = lines[y - 1]?.error;
         let inputLine = input.slice(y * width, (y + 1) * width);
-        let line = decimate(inputLine, allColors, 4, error);
+        let line = decimate(inputLine, allColors, 4, error, y);
         lines.push(line);
     }
     return {