diff --git a/CamScanner.cs b/CamScanner.cs
index 356c5f3..447d216 100644
--- a/CamScanner.cs
+++ b/CamScanner.cs
@@ -420,42 +420,49 @@ public static class DocumentScanner
             inkData[i] = (byte)(255 - val); // 墨迹强度：0=无墨, 255=纯黑
         }
 
-        // 计算局部方差图（用灰度图，不是墨迹图）
-        // 文字区域：灰度变化大（笔画边缘），方差高
-        // 折痕区域：灰度缓慢变化，方差低
-        // 用简化方法：|gray - 局部均值| 的局部均值 ≈ 局部标准差
+        // 计算两级局部方差：
+        //   小核(7)：检测文字笔画（高频），文字处方差高
+        //   大核(31)：检测折痕渐变（低频），折痕处方差低
+        // 只有两级方差都低时才抑制，避免误伤折痕附近的文字
         Mat grayMat = new Mat(h, w, MatType.CV_8U, grayData);
-        Mat localMean = new Mat();
-        int varKernSize = 15;
-        Cv2.Blur(grayMat, localMean, new OpenCvSharp.Size(varKernSize, varKernSize));
 
-        // |gray - localMean|
-        Mat diff = new Mat();
-        Cv2.Absdiff(grayMat, localMean, diff);
-        localMean.Dispose();
+        // 小核方差（保护文字）
+        Mat localMeanS = new Mat();
+        Cv2.Blur(grayMat, localMeanS, new OpenCvSharp.Size(7, 7));
+        Mat diffS = new Mat();
+        Cv2.Absdiff(grayMat, localMeanS, diffS);
+        localMeanS.Dispose();
+        Mat localVarS = new Mat();
+        Cv2.Blur(diffS, localVarS, new OpenCvSharp.Size(7, 7));
+        diffS.Dispose();
 
-        // 对 diff 再做一次均值模糊，得到局部方差的近似
-        Mat localVar = new Mat();
-        Cv2.Blur(diff, localVar, new OpenCvSharp.Size(varKernSize, varKernSize));
-        diff.Dispose();
+        // 大核方差（检测折痕）
+        Mat localMeanL = new Mat();
+        Cv2.Blur(grayMat, localMeanL, new OpenCvSharp.Size(31, 31));
+        Mat diffL = new Mat();
+        Cv2.Absdiff(grayMat, localMeanL, diffL);
+        localMeanL.Dispose();
+        Mat localVarL = new Mat();
+        Cv2.Blur(diffL, localVarL, new OpenCvSharp.Size(31, 31));
+        diffL.Dispose();
         grayMat.Dispose();
 
-        byte[] varData = new byte[w * h];
-        Marshal.Copy(localVar.Data, varData, 0, varData.Length);
-        localVar.Dispose();
-
-        // 用局部方差来决定是否抑制
-        // 高方差（> 阈值）= 文字，保留
-        // 低方差 + 有墨迹 = 折痕/阴影，抑制
-        int varThresh = 8; // 方差阈值，低于此值认为是平坦区域
+        byte[] varDataS = new byte[w * h];
+        byte[] varDataL = new byte[w * h];
+        Marshal.Copy(localVarS.Data, varDataS, 0, varDataS.Length);
+        Marshal.Copy(localVarL.Data, varDataL, 0, varDataL.Length);
+        localVarS.Dispose();
+        localVarL.Dispose();
 
+        // 抑制逻辑：
+        //   小核方差 < 5 且 大核方差 < 12 → 确定是平坦渐变区域（折痕/阴影）
+        //   小核方差 >= 5 → 有文字笔画，不抑制（即使大核方差低）
         for (int i = 0; i < resultData.Length; i++)
         {
-            if (inkData[i] > 10 && varData[i] < varThresh)
+            if (inkData[i] > 10 && varDataS[i] < 5 && varDataL[i] < 12)
             {
-                // 有墨迹但局部方差低 → 折痕/阴影，推向白色
-                // 抑制程度和方差成正比：方差越低抑制越强
-                double suppressRatio = (double)varData[i] / varThresh;
+                // 两级方差都低 → 折痕/阴影
+                double suppressRatio = (double)varDataS[i] / 5.0;
                 int origVal = resultData[i];
                 resultData[i] = (byte)(origVal + (int)((255 - origVal) * (1.0 - suppressRatio)));
             }