白底/黑底检测：轮廓与最远弦度量，UI 分色与标注优化

- 算子：输出轮廓顶点及顶点间最远弦（微米标定与原先一致）

- 视图：实线轮廓；白底红/黑底绿；尺寸文字置于 ROI 外右侧垂直居中

- 事件与 MainViewModel 载荷改为 BackgroundDefectDetectionItem

Co-authored-by: Cursor <cursoragent@cursor.com>

XP.ImageProcessing.Processors/检测分析/BackgroundDefectAnalyzer.cs

@@ -2,10 +2,11 @@
 // Copyright © 2026 Hexagon Technology Center GmbH. All Rights Reserved.
 // 文件名: BackgroundDefectAnalyzer.cs
 // 描述: 白底/黑底对比下的缺陷斑点分析（仅 ROI 内计算，不接入流水线算子）
-// 算法: Otsu 二值化 → 形态学开运算 → 外轮廓 → 面积过滤 → 外接矩形等效圆
+// 算法: Otsu 二值化 → 形态学开运算 → 外轮廓 → 面积过滤 → 轮廓顶点最远弦（物理长度与历史等效直径同一标定：mm/px → μm）
 // 作者: 李伟 wei.lw.li@hexagon.com
 // ============================================================================
 
+using System.Collections.Generic;
 using System.Drawing;
 using Emgu.CV;
 using Emgu.CV.CvEnum;
@@ -27,9 +28,15 @@ public enum BackgroundDefectMode
 }
 
 /// <summary>
-/// 单个斑点，坐标相对于输入 ROI 左上角；<see cref="SizeMicrometers"/> 与主界面标注逻辑一致（等效直径，微米）。
+/// 单个斑点：轮廓顶点相对于 ROI 左上角；<see cref="MaxChordMicrometers"/> 为轮廓顶点间欧氏距离最大值（微米）。
 /// </summary>
-public readonly record struct BackgroundDefectBlob(Point CenterInRoi, int RadiusPixels, double SizeMicrometers);
+public sealed class BackgroundDefectBlob
+{
+    public Point[] ContourInRoi { get; init; } = Array.Empty<Point>();
+    public double MaxChordMicrometers { get; init; }
+    public Point MaxChordEndAInRoi { get; init; }
+    public Point MaxChordEndBInRoi { get; init; }
+}
 
 /// <summary>
 /// 在灰度 ROI 上执行底色缺陷斑点检测。调用方负责构造与释放 <paramref name="roiGray"/>。
@@ -42,7 +49,7 @@ public static class BackgroundDefectAnalyzer
     /// <param name="roiGray">ROI 灰度图（单通道 8 位）。</param>
     /// <param name="mode">白底或黑底模式。</param>
     /// <param name="minAreaPixels">轮廓最小面积（像素²），小于此值的轮廓丢弃。</param>
-    /// <param name="mmPerPixel">像素物理尺寸（毫米/像素），用于等效直径换算。</param>
+    /// <param name="mmPerPixel">像素物理尺寸（毫米/像素），用于轮廓最远弦换算为微米。</param>
     /// <param name="morphKernelSize">形态学开运算核尺寸（奇数，默认 3）。</param>
     public static List<BackgroundDefectBlob> DetectBlobs(
         Image<Gray, byte> roiGray,
@@ -84,19 +91,56 @@ public static class BackgroundDefectAnalyzer
             double area = CvInvoke.ContourArea(contours[i]);
             if (area < minAreaPixels) continue;
 
-            var boundRect = CvInvoke.BoundingRectangle(contours[i]);
-            double radiusF = Math.Max(boundRect.Width, boundRect.Height) / 2.0;
-            var centerF = new PointF(
-                boundRect.X + boundRect.Width / 2.0f,
-                boundRect.Y + boundRect.Height / 2.0f);
+            int n = contours[i].Size;
+            if (n < 2) continue;
 
-            var centerInRoi = new Point((int)centerF.X, (int)centerF.Y);
-            int radiusPx = (int)radiusF;
-            double sizeMicrometers = radiusF * 2.0 * mmPerPixel * 1000.0;
+            var pts = new Point[n];
+            for (int j = 0; j < n; j++)
+                pts[j] = contours[i][j];
 
-            result.Add(new BackgroundDefectBlob(centerInRoi, radiusPx, sizeMicrometers));
+            MaxChordInPixelSpace(pts, out double maxChordPx, out Point pa, out Point pb);
+            double maxChordMicrometers = maxChordPx * mmPerPixel * 1000.0;
+
+            result.Add(new BackgroundDefectBlob
+            {
+                ContourInRoi = pts,
+                MaxChordMicrometers = maxChordMicrometers,
+                MaxChordEndAInRoi = pa,
+                MaxChordEndBInRoi = pb
+            });
         }
 
         return result;
     }
+
+    /// <summary>轮廓顶点集合上的最远点对（欧氏距离，像素）。</summary>
+    private static void MaxChordInPixelSpace(Point[] pts, out double maxChordPx, out Point a, out Point b)
+    {
+        maxChordPx = 0;
+        a = pts[0];
+        b = pts.Length > 1 ? pts[1] : pts[0];
+        long bestSq = 0;
+        int bestI = 0, bestJ = 1;
+        int n = pts.Length;
+        for (int i = 0; i < n; i++)
+        {
+            int iX = pts[i].X, iY = pts[i].Y;
+            for (int j = i + 1; j < n; j++)
+            {
+                long dx = iX - pts[j].X;
+                long dy = iY - pts[j].Y;
+                long sq = dx * dx + dy * dy;
+                if (sq > bestSq)
+                {
+                    bestSq = sq;
+                    bestI = i;
+                    bestJ = j;
+                }
+            }
+        }
+
+        a = pts[bestI];
+        b = pts[bestJ];
+        maxChordPx = Math.Sqrt(bestSq);
+    }
 }