From 27b0098bf9d38c8e1679c5488ccf10f708a9b2f9 Mon Sep 17 00:00:00 2001
From: 134 <a134@134deMacBook-Pro.local>
Date: Fri, 3 Jul 2026 20:02:00 +0800
Subject: [PATCH] fix: clean cutout alpha for scale drafts

---
 app/api/canvas/local-edit/route.ts | 46 ++++++++++++++++++++----------
 1 file changed, 31 insertions(+), 15 deletions(-)

diff --git a/app/api/canvas/local-edit/route.ts b/app/api/canvas/local-edit/route.ts
index 06bc92a5b..e5ac066c7 100644
--- a/app/api/canvas/local-edit/route.ts
+++ b/app/api/canvas/local-edit/route.ts
@@ -111,6 +111,7 @@ const SCALE_ADJUST_STRUCTURE_LOCK_MIN_MASK_RATIO = 0.006;
 const SCALE_ADJUST_STRUCTURE_LOCK_COMPONENT_MIN_RATIO = 0.00018;
 const SCALE_ADJUST_RMBG_MIN_ALPHA_RATIO = 0.012;
 const SCALE_ADJUST_RMBG_MAX_SOLID_ALPHA_RATIO = 0.92;
+const SCALE_ADJUST_RMBG_ALPHA_CLEAN_THRESHOLD = 42;
 const MIN_REGION_EDGE_PX = 24;
 const SCALE_ADJUST_OPERATION = "scale-adjust";
 type LocalEditOperation = "local-edit" | typeof SCALE_ADJUST_OPERATION;
@@ -1708,17 +1709,28 @@ function getScaleAdjustAlphaBoundingBox(params: {
   };
 }
 
-function extractScaleAdjustAlphaChannel(params: {
-  height: number;
+function cleanScaleAdjustAlphaChannel(params: {
   rawRgba: Buffer;
-  width: number;
+  threshold?: number;
 }) {
-  const { height, rawRgba, width } = params;
-  const alpha = Buffer.alloc(width * height);
-  for (let index = 0; index < width * height; index += 1) {
-    alpha[index] = rawRgba[index * 4 + 3] || 0;
+  const { rawRgba, threshold = SCALE_ADJUST_RMBG_ALPHA_CLEAN_THRESHOLD } = params;
+  const pixelCount = Math.floor(rawRgba.length / 4);
+  const cleanedRaw = Buffer.from(rawRgba);
+  const cleanedAlpha = Buffer.alloc(pixelCount);
+  const range = Math.max(1, 255 - threshold);
+
+  for (let index = 0; index < pixelCount; index += 1) {
+    const alphaIndex = index * 4 + 3;
+    const sourceAlpha = rawRgba[alphaIndex] || 0;
+    const nextAlpha =
+      sourceAlpha < threshold
+        ? 0
+        : Math.max(0, Math.min(255, Math.round(((sourceAlpha - threshold) / range) * 255)));
+    cleanedRaw[alphaIndex] = nextAlpha;
+    cleanedAlpha[index] = nextAlpha;
   }
-  return alpha;
+
+  return { cleanedAlpha, cleanedRaw };
 }
 
 async function resizeScaleAdjustAlphaMask(params: {
@@ -1795,9 +1807,17 @@ async function buildScaleAdjustRmbgStructureLockedComposite(params: {
       .ensureAlpha()
       .raw()
       .toBuffer();
+    const { cleanedAlpha, cleanedRaw } = cleanScaleAdjustAlphaChannel({
+      rawRgba: cutoutRaw,
+    });
+    const cleanedCutout = await sharp(cleanedRaw, {
+      raw: { channels: 4, height: cutoutHeight, width: cutoutWidth },
+    })
+      .png({ compressionLevel: 6 })
+      .toBuffer();
     const alphaBbox = getScaleAdjustAlphaBoundingBox({
       height: cutoutHeight,
-      rawRgba: cutoutRaw,
+      rawRgba: cleanedRaw,
       width: cutoutWidth,
     });
     if (!alphaBbox) return null;
@@ -1816,11 +1836,7 @@ async function buildScaleAdjustRmbgStructureLockedComposite(params: {
     const sameSizeCutout =
       Math.abs(cutoutWidth - placement.sourceBox.width) <= 2 &&
       Math.abs(cutoutHeight - placement.sourceBox.height) <= 2;
-    const fullAlphaMask = extractScaleAdjustAlphaChannel({
-      height: cutoutHeight,
-      rawRgba: cutoutRaw,
-      width: cutoutWidth,
-    });
+    const fullAlphaMask = cleanedAlpha;
     const sourceMaskBuffer = sameSizeCutout
       ? fullAlphaMask
       : await resizeScaleAdjustAlphaMask({
@@ -1852,7 +1868,7 @@ async function buildScaleAdjustRmbgStructureLockedComposite(params: {
       maskBuffer: Buffer.from(sourceWashMask),
     });
 
-    const subjectCutout = await sharp(normalizedCutout, { failOn: "none" })
+    const subjectCutout = await sharp(cleanedCutout, { failOn: "none" })
       .extract(alphaBbox)
       .png({ compressionLevel: 6 })
       .toBuffer();