重写阴影处理：改为边缘扫描法，只处理四周边缘阴影

OTSU全局阈值会把文字密集区域误判为阴影。改为从图像四边向内
逐列/逐行扫描，遇到连续暗像素（低于纸面亮度55%）标记为阴影，
遇到亮像素立即停止。这样只会处理边缘连续暗区域，不会误伤
文档中间的文字。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CamScanner.cs

@@ -374,7 +374,7 @@ public static class DocumentScanner
             }
         }
 
-        // 墨迹映射（不做阴影判断，先全部正常处理）
+        // 墨迹映射
         for (int i = 0; i < grayData.Length; i++)
         {
             int ink = bgData[i] - grayData[i];
@@ -383,7 +383,6 @@ public static class DocumentScanner
             double inkNorm = (double)ink / ink95;
             if (inkNorm > 1.0) inkNorm = 1.0;
 
-            // 非线性加深：pow(x, 0.45) 让浅墨迹也变深
             double darkness = Math.Pow(inkNorm, 0.45);
 
             int val = (int)(255.0 * (1.0 - darkness));
@@ -392,6 +391,85 @@ public static class DocumentScanner
             resultData[i] = (byte)val;
         }
 
+        // --- 阴影修复：从边缘向内扫描，把连续暗像素区域设为白色 ---
+        // 阴影只出现在文档四周边缘（拍照翘边/光照不均）
+        // 从上下左右四个方向向内扫描原始灰度，遇到连续暗区域就标记为阴影
+        byte[] shadowFlag = new byte[w * h]; // 0=正常, 1=阴影
+
+        // 计算"正常纸面亮度"：取灰度图中心区域的均值
+        int cx1 = w / 4;
+        int cx2 = w * 3 / 4;
+        int cy1 = h / 4;
+        int cy2 = h * 3 / 4;
+        long centerSum = 0;
+        int centerCount = 0;
+        for (int y = cy1; y < cy2; y++)
+        {
+            for (int x = cx1; x < cx2; x++)
+            {
+                centerSum += grayData[y * w + x];
+                centerCount++;
+            }
+        }
+        int paperBright = (int)(centerSum / Math.Max(centerCount, 1));
+        // 阴影判定：原始灰度低于纸面亮度的55%
+        int darkThresh = (int)(paperBright * 0.55);
+
+        // 从四个边缘向内扫描
+        int maxScanDepth = Math.Max(w, h) / 8; // 最多扫描图像尺寸的1/8
+
+        // 上边缘
+        for (int x = 0; x < w; x++)
+        {
+            for (int y = 0; y < Math.Min(maxScanDepth, h); y++)
+            {
+                if (grayData[y * w + x] < darkThresh)
+                    shadowFlag[y * w + x] = 1;
+                else
+                    break; // 遇到亮像素就停止
+            }
+        }
+        // 下边缘
+        for (int x = 0; x < w; x++)
+        {
+            for (int y = h - 1; y >= Math.Max(0, h - maxScanDepth); y--)
+            {
+                if (grayData[y * w + x] < darkThresh)
+                    shadowFlag[y * w + x] = 1;
+                else
+                    break;
+            }
+        }
+        // 左边缘
+        for (int y = 0; y < h; y++)
+        {
+            for (int x = 0; x < Math.Min(maxScanDepth, w); x++)
+            {
+                if (grayData[y * w + x] < darkThresh)
+                    shadowFlag[y * w + x] = 1;
+                else
+                    break;
+            }
+        }
+        // 右边缘
+        for (int y = 0; y < h; y++)
+        {
+            for (int x = w - 1; x >= Math.Max(0, w - maxScanDepth); x--)
+            {
+                if (grayData[y * w + x] < darkThresh)
+                    shadowFlag[y * w + x] = 1;
+                else
+                    break;
+            }
+        }
+
+        // 把阴影区域的结果设为白色
+        for (int i = 0; i < resultData.Length; i++)
+        {
+            if (shadowFlag[i] == 1)
+                resultData[i] = 255;
+        }
+
         Mat enhanced = new Mat(h, w, MatType.CV_8U);
         Marshal.Copy(resultData, 0, enhanced.Data, resultData.Length);
 
@@ -410,48 +488,6 @@ public static class DocumentScanner
         Cv2.Threshold(sharpened, sharpened, 220, 255, ThresholdTypes.Trunc);
         Cv2.ConvertScaleAbs(sharpened, sharpened, 255.0 / 220.0, 0);
 
-        // --- g: 阴影区域后处理 ---
-        // 用小核模糊的原始灰度做区域级阴影检测（不是逐像素，避免误伤文字）
-        // 阴影 = 大面积暗区域，文字 = 小面积暗像素散布在亮背景中
-        int shadowBlurSize = Math.Max(w, h) / 15;
-        if (shadowBlurSize % 2 == 0) shadowBlurSize++;
-        if (shadowBlurSize < 31) shadowBlurSize = 31;
-
-        Mat grayBlurred = new Mat();
-        Cv2.GaussianBlur(gray, grayBlurred, new OpenCvSharp.Size(shadowBlurSize, shadowBlurSize), 0);
-
-        // 模糊后的灰度图：阴影区域整体偏暗，文字区域因为周围是白纸所以模糊后仍然亮
-        // 找阈值：用 OTSU 自动找
-        Mat shadowMask = new Mat();
-        Cv2.Threshold(grayBlurred, shadowMask, 0, 255, ThresholdTypes.Binary | ThresholdTypes.Otsu);
-        grayBlurred.Dispose();
-
-        // shadowMask: 亮区域=255(正常), 暗区域=0(阴影)
-        // 对 mask 做膨胀，扩大阴影区域覆盖范围，避免边缘残留
-        Mat dilateK = Cv2.GetStructuringElement(MorphShapes.Ellipse, new OpenCvSharp.Size(15, 15));
-        Mat shadowMaskInv = new Mat();
-        Cv2.BitwiseNot(shadowMask, shadowMaskInv); // 反转：阴影=255
-        Cv2.Dilate(shadowMaskInv, shadowMaskInv, dilateK);
-        dilateK.Dispose();
-
-        // 在阴影区域把结果设为白色
-        byte[] sharpenedData = new byte[w * h];
-        byte[] maskData = new byte[w * h];
-        Marshal.Copy(sharpened.Data, sharpenedData, 0, sharpenedData.Length);
-        Marshal.Copy(shadowMaskInv.Data, maskData, 0, maskData.Length);
-        shadowMask.Dispose();
-        shadowMaskInv.Dispose();
-
-        for (int i = 0; i < sharpenedData.Length; i++)
-        {
-            if (maskData[i] > 128)
-            {
-                // 阴影区域 → 白色
-                sharpenedData[i] = 255;
-            }
-        }
-        Marshal.Copy(sharpenedData, 0, sharpened.Data, sharpenedData.Length);
-
         // 转回3通道
         Mat output = new Mat();
         Cv2.CvtColor(sharpened, output, ColorConversionCodes.GRAY2BGR);