Improve transition edge cleanup

app/page.tsx

@@ -360,17 +360,15 @@ function sampleDominantRegions(
 
 function cleanThinTransitionBands(colors: Array<BeadColor | null>, width: number, height: number) {
   const cleaned = [...colors];
-  const usage = new Map<string, number>();
-  colors.forEach((color) => { if (color) usage.set(color.code, (usage.get(color.code) ?? 0) + 1); });
-  const maximumTransitionUsage = Math.max(4, Math.ceil(width * height * 0.015));
   let changed = 0;
 
   for (let row = 0; row < height; row++) {
     for (let column = 0; column < width; column++) {
       const index = row * width + column;
       const current = colors[index];
-      if (!current || (usage.get(current.code) ?? 0) > maximumTransitionUsage) continue;
+      if (!current) continue;
       const neighbors = new Map<string, { color: BeadColor; count: number }>();
+      let sameColorNeighbors = 0;
       for (let rowOffset = -1; rowOffset <= 1; rowOffset++) {
         for (let columnOffset = -1; columnOffset <= 1; columnOffset++) {
           if (rowOffset === 0 && columnOffset === 0) continue;
@@ -378,12 +376,20 @@ function cleanThinTransitionBands(colors: Array<BeadColor | null>, width: number
           const neighborColumn = column + columnOffset;
           if (neighborRow < 0 || neighborColumn < 0 || neighborRow >= height || neighborColumn >= width) continue;
           const neighbor = colors[neighborRow * width + neighborColumn];
-          if (!neighbor || neighbor.code === current.code) continue;
+          if (!neighbor) continue;
+          if (neighbor.code === current.code) {
+            sameColorNeighbors += 1;
+            continue;
+          }
           const entry = neighbors.get(neighbor.code) ?? { color: neighbor, count: 0 };
           entry.count += 1;
           neighbors.set(neighbor.code, entry);
         }
       }
+      // A true gradient band has broad same-color support. Anti-aliased edge
+      // colors form a one-cell-wide chain and have at most two same-color
+      // neighbors, regardless of how often that edge color occurs globally.
+      if (sameColorNeighbors > 2) continue;
       const candidates = [...neighbors.values()].sort((a, b) => b.count - a.count).slice(0, 3);
       let replacement: BeadColor | null = null;
       let replacementSupport = 0;