diff --git a/XplorePlane/Events/MeasurementToolEvent.cs b/XplorePlane/Events/MeasurementToolEvent.cs
index 9964acb..4356e45 100644
--- a/XplorePlane/Events/MeasurementToolEvent.cs
+++ b/XplorePlane/Events/MeasurementToolEvent.cs
@@ -30,4 +30,25 @@ namespace XplorePlane.Events
     /// 行灰度分布切换事件
     /// </summary>
     public class ToggleLineProfileEvent : PubSubEvent { }
+
+    /// <summary>
+    /// 白底检测事件（进入ROI绘制模式）
+    /// </summary>
+    public class WhiteBackgroundDetectionEvent : PubSubEvent { }
+
+    /// <summary>
+    /// 白底检测ROI绘制完成事件
+    /// </summary>
+    public class WhiteBackgroundRoiDrawnEvent : PubSubEvent<System.Windows.Int32Rect> { }
+
+    /// <summary>
+    /// 白底检测结果事件
+    /// </summary>
+    public class WhiteBackgroundResultEvent : PubSubEvent<WhiteBackgroundResultPayload> { }
+
+    public class WhiteBackgroundResultPayload
+    {
+        public System.Drawing.Rectangle RoiRect { get; set; }
+        public System.Collections.Generic.List<(System.Drawing.Point center, int radius, double sizeMm)> Detections { get; set; }
+    }
 }
diff --git a/XplorePlane/ViewModels/Main/MainViewModel.cs b/XplorePlane/ViewModels/Main/MainViewModel.cs
index 151e895..6f99e44 100644
--- a/XplorePlane/ViewModels/Main/MainViewModel.cs
+++ b/XplorePlane/ViewModels/Main/MainViewModel.cs
@@ -275,6 +275,9 @@ namespace XplorePlane.ViewModels
             _eventAggregator.GetEvent<PipelinePreviewUpdatedEvent>()
                 .Subscribe(OnPipelinePreviewUpdated, ThreadOption.UIThread);
 
+            _eventAggregator.GetEvent<WhiteBackgroundRoiDrawnEvent>()
+                .Subscribe(OnWhiteBackgroundRoiDrawn, ThreadOption.UIThread);
+
             NavigationTree = new ObservableCollection<object>();
 
             NavigateHomeCommand = new DelegateCommand(OnNavigateHome);
@@ -947,8 +950,106 @@ namespace XplorePlane.ViewModels
         private void ExecuteWhiteBackgroundDetection()
         {
             if (!CheckImageLoaded()) return;
-            _logger.Info("White background detection triggered.");
-            // TODO: 实现白底检测逻辑
+            _logger.Info("White background detection: entering ROI draw mode.");
+            _eventAggregator.GetEvent<WhiteBackgroundDetectionEvent>().Publish();
+            StatusMessage = "白底检测：请在图像上拖拽绘制矩形ROI";
+        }
+
+        private void OnWhiteBackgroundRoiDrawn(System.Windows.Int32Rect roi)
+        {
+            try
+            {
+                var viewportVm = _containerProvider.Resolve<ViewportPanelViewModel>();
+                var imageSource = viewportVm?.ImageSource as System.Windows.Media.Imaging.BitmapSource;
+                if (imageSource == null) return;
+
+                // 转为 Gray8
+                System.Windows.Media.Imaging.BitmapSource gray8;
+                if (imageSource.Format != System.Windows.Media.PixelFormats.Gray8)
+                    gray8 = new System.Windows.Media.Imaging.FormatConvertedBitmap(
+                        imageSource, System.Windows.Media.PixelFormats.Gray8, null, 0);
+                else
+                    gray8 = imageSource;
+
+                int imgW = gray8.PixelWidth;
+                int imgH = gray8.PixelHeight;
+
+                // 限制ROI在图像范围内
+                int rx = Math.Clamp(roi.X, 0, imgW - 1);
+                int ry = Math.Clamp(roi.Y, 0, imgH - 1);
+                int rw = Math.Clamp(roi.Width, 1, imgW - rx);
+                int rh = Math.Clamp(roi.Height, 1, imgH - ry);
+
+                // 提取ROI区域像素
+                byte[] roiPixels = new byte[rw * rh];
+                gray8.CopyPixels(new System.Windows.Int32Rect(rx, ry, rw, rh), roiPixels, rw, 0);
+
+                // 使用EmguCV处理
+                using var roiImage = new Emgu.CV.Image<Emgu.CV.Structure.Gray, byte>(rw, rh);
+                for (int y = 0; y < rh; y++)
+                    for (int x = 0; x < rw; x++)
+                        roiImage.Data[y, x, 0] = roiPixels[y * rw + x];
+
+                // Otsu阈值分割（白底检测黑色区域：反转后黑色区域变白）
+                using var binary = new Emgu.CV.Image<Emgu.CV.Structure.Gray, byte>(rw, rh);
+                Emgu.CV.CvInvoke.Threshold(roiImage, binary, 0, 255,
+                    Emgu.CV.CvEnum.ThresholdType.BinaryInv | Emgu.CV.CvEnum.ThresholdType.Otsu);
+
+                // 形态学开运算去噪
+                using var kernel = Emgu.CV.CvInvoke.GetStructuringElement(
+                    Emgu.CV.CvEnum.ElementShape.Ellipse, new System.Drawing.Size(3, 3), new System.Drawing.Point(-1, -1));
+                Emgu.CV.CvInvoke.MorphologyEx(binary, binary,
+                    Emgu.CV.CvEnum.MorphOp.Open, kernel, new System.Drawing.Point(-1, -1), 1,
+                    Emgu.CV.CvEnum.BorderType.Default, new Emgu.CV.Structure.MCvScalar(0));
+
+                // 查找轮廓
+                using var contours = new Emgu.CV.Util.VectorOfVectorOfPoint();
+                using var hierarchy = new Emgu.CV.Mat();
+                Emgu.CV.CvInvoke.FindContours(binary, contours, hierarchy,
+                    Emgu.CV.CvEnum.RetrType.External, Emgu.CV.CvEnum.ChainApproxMethod.ChainApproxSimple);
+
+                // 过滤小区域（最小面积默认50像素²）
+                const int minArea = 50;
+                double pixelSize = 0.139; // mm/pixel，默认值（可从比例尺获取）
+
+                var detections = new System.Collections.Generic.List<(System.Drawing.Point center, int radius, double sizeMm)>();
+
+                for (int i = 0; i < contours.Size; i++)
+                {
+                    double area = Emgu.CV.CvInvoke.ContourArea(contours[i]);
+                    if (area < minArea) continue;
+
+                    // 最小外接圆 - 使用外接矩形计算
+                    var boundRect = Emgu.CV.CvInvoke.BoundingRectangle(contours[i]);
+                    double radiusF = Math.Max(boundRect.Width, boundRect.Height) / 2.0;
+                    var centerF = new System.Drawing.PointF(
+                        boundRect.X + boundRect.Width / 2.0f,
+                        boundRect.Y + boundRect.Height / 2.0f);
+
+                    // 转换到全局坐标
+                    var globalCenter = new System.Drawing.Point((int)centerF.X + rx, (int)centerF.Y + ry);
+                    double diameterMm = radiusF * 2 * pixelSize * 1000; // 转μm
+
+                    detections.Add((globalCenter, (int)radiusF, diameterMm));
+                }
+
+                // 发布结果用于绘制（通过OutputData模式传递给ViewportPanelView）
+                _eventAggregator.GetEvent<WhiteBackgroundResultEvent>().Publish(
+                    new WhiteBackgroundResultPayload
+                    {
+                        RoiRect = new System.Drawing.Rectangle(rx, ry, rw, rh),
+                        Detections = detections
+                    });
+
+                StatusMessage = $"白底检测完成：检测到 {detections.Count} 个黑色区域";
+                _logger.Info("White background detection: found {Count} dark regions in ROI ({X},{Y},{W},{H})",
+                    detections.Count, rx, ry, rw, rh);
+            }
+            catch (Exception ex)
+            {
+                _logger.Error(ex, "White background detection failed");
+                StatusMessage = $"白底检测失败: {ex.Message}";
+            }
         }
 
         private void ExecuteBlackBackgroundDetection()
diff --git a/XplorePlane/Views/Main/ViewportPanelView.xaml.cs b/XplorePlane/Views/Main/ViewportPanelView.xaml.cs
index 50f21c6..9be9e3d 100644
--- a/XplorePlane/Views/Main/ViewportPanelView.xaml.cs
+++ b/XplorePlane/Views/Main/ViewportPanelView.xaml.cs
@@ -138,6 +138,26 @@ namespace XplorePlane.Views
                 {
                     ToggleLineProfile();
                 }, Prism.Events.ThreadOption.UIThread);
+
+                // 白底检测：进入ROI绘制模式
+                ea2?.GetEvent<WhiteBackgroundDetectionEvent>().Subscribe(() =>
+                {
+                    _whiteDetectDrawing = false;
+                    _whiteDetectMode = true;
+                    // 注册鼠标事件（只注册一次）
+                    RoiCanvas.PreviewMouseLeftButtonDown -= OnMainCanvasPreviewMouseDown;
+                    RoiCanvas.PreviewMouseLeftButtonDown += OnMainCanvasPreviewMouseDown;
+                    RoiCanvas.PreviewMouseMove -= OnMainCanvasPreviewMouseMove;
+                    RoiCanvas.PreviewMouseMove += OnMainCanvasPreviewMouseMove;
+                    RoiCanvas.PreviewMouseLeftButtonUp -= OnMainCanvasPreviewMouseUp;
+                    RoiCanvas.PreviewMouseLeftButtonUp += OnMainCanvasPreviewMouseUp;
+                }, Prism.Events.ThreadOption.UIThread);
+
+                // 白底检测：渲染结果
+                ea2?.GetEvent<WhiteBackgroundResultEvent>().Subscribe(payload =>
+                {
+                    RenderWhiteBackgroundResult(payload);
+                }, Prism.Events.ThreadOption.UIThread);
             }
             catch { }
         }
@@ -380,6 +400,175 @@ namespace XplorePlane.Views
 
         #endregion
 
+        #region 白底检测
+
+        private bool _whiteDetectMode;
+        private bool _whiteDetectDrawing;
+        private System.Windows.Point _whiteDetectStart;
+        private System.Windows.Shapes.Rectangle _whiteDetectPreview;
+        private readonly System.Collections.Generic.List<System.Windows.UIElement> _whiteDetectOverlays = new();
+
+        // 需要在 mainCanvas 的 MouseDown/Move/Up 中处理
+        // 由于 PolygonRoiCanvas 内部已经处理了鼠标事件，我们通过 PreviewMouse 事件来拦截
+
+        private void OnMainCanvasPreviewMouseDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
+        {
+            if (!_whiteDetectMode || e.LeftButton != System.Windows.Input.MouseButtonState.Pressed) return;
+
+            var canvas = FindChildByName<System.Windows.Controls.Canvas>(RoiCanvas, "mainCanvas");
+            if (canvas == null) return;
+
+            _whiteDetectStart = e.GetPosition(canvas);
+            _whiteDetectDrawing = true;
+
+            // 创建预览矩形（不清除之前的检测结果）
+            _whiteDetectPreview = new System.Windows.Shapes.Rectangle
+            {
+                Stroke = System.Windows.Media.Brushes.Blue,
+                StrokeThickness = 1,
+                StrokeDashArray = new System.Windows.Media.DoubleCollection { 4, 2 }
+            };
+            System.Windows.Controls.Canvas.SetLeft(_whiteDetectPreview, _whiteDetectStart.X);
+            System.Windows.Controls.Canvas.SetTop(_whiteDetectPreview, _whiteDetectStart.Y);
+            canvas.Children.Add(_whiteDetectPreview);
+
+            RoiCanvas.CaptureMouse();
+            e.Handled = true;
+        }
+
+        private void OnMainCanvasPreviewMouseMove(object sender, System.Windows.Input.MouseEventArgs e)
+        {
+            if (!_whiteDetectDrawing || _whiteDetectPreview == null) return;
+
+            var canvas = FindChildByName<System.Windows.Controls.Canvas>(RoiCanvas, "mainCanvas");
+            if (canvas == null) return;
+
+            var current = e.GetPosition(canvas);
+            double x = Math.Min(_whiteDetectStart.X, current.X);
+            double y = Math.Min(_whiteDetectStart.Y, current.Y);
+            double w = Math.Abs(current.X - _whiteDetectStart.X);
+            double h = Math.Abs(current.Y - _whiteDetectStart.Y);
+
+            System.Windows.Controls.Canvas.SetLeft(_whiteDetectPreview, x);
+            System.Windows.Controls.Canvas.SetTop(_whiteDetectPreview, y);
+            _whiteDetectPreview.Width = Math.Max(1, w);
+            _whiteDetectPreview.Height = Math.Max(1, h);
+        }
+
+        private void OnMainCanvasPreviewMouseUp(object sender, System.Windows.Input.MouseButtonEventArgs e)
+        {
+            if (!_whiteDetectDrawing) return;
+
+            _whiteDetectDrawing = false;
+            _whiteDetectMode = false;
+            RoiCanvas.ReleaseMouseCapture();
+
+            var canvas = FindChildByName<System.Windows.Controls.Canvas>(RoiCanvas, "mainCanvas");
+            if (canvas == null) return;
+
+            var end = e.GetPosition(canvas);
+            int x = (int)Math.Min(_whiteDetectStart.X, end.X);
+            int y = (int)Math.Min(_whiteDetectStart.Y, end.Y);
+            int w = (int)Math.Abs(end.X - _whiteDetectStart.X);
+            int h = (int)Math.Abs(end.Y - _whiteDetectStart.Y);
+
+            // 移除预览矩形
+            if (_whiteDetectPreview != null)
+            {
+                canvas.Children.Remove(_whiteDetectPreview);
+                _whiteDetectPreview = null;
+            }
+
+            if (w < 10 || h < 10) return; // 太小忽略
+
+            // 发布ROI绘制完成事件
+            try
+            {
+                var ea = ContainerLocator.Current?.Resolve<Prism.Events.IEventAggregator>();
+                ea?.GetEvent<WhiteBackgroundRoiDrawnEvent>().Publish(new System.Windows.Int32Rect(x, y, w, h));
+            }
+            catch { }
+
+            e.Handled = true;
+        }
+
+        private void RenderWhiteBackgroundResult(WhiteBackgroundResultPayload payload)
+        {
+            var canvas = FindChildByName<System.Windows.Controls.Canvas>(RoiCanvas, "mainCanvas");
+            if (canvas == null || payload?.Detections == null) return;
+
+            // 绘制ROI矩形（蓝色实线）
+            var roiRect = new System.Windows.Shapes.Rectangle
+            {
+                Stroke = System.Windows.Media.Brushes.Blue,
+                StrokeThickness = 1,
+                Width = payload.RoiRect.Width,
+                Height = payload.RoiRect.Height,
+                IsHitTestVisible = false
+            };
+            System.Windows.Controls.Canvas.SetLeft(roiRect, payload.RoiRect.X);
+            System.Windows.Controls.Canvas.SetTop(roiRect, payload.RoiRect.Y);
+            canvas.Children.Add(roiRect);
+            _whiteDetectOverlays.Add(roiRect);
+
+            // 绘制每个检测到的黑色区域
+            foreach (var (center, radius, sizeMm) in payload.Detections)
+            {
+                // 红色虚线圆
+                var circle = new System.Windows.Shapes.Ellipse
+                {
+                    Stroke = System.Windows.Media.Brushes.Red,
+                    StrokeThickness = 1,
+                    StrokeDashArray = new System.Windows.Media.DoubleCollection { 4, 2 },
+                    Width = radius * 2,
+                    Height = radius * 2,
+                    IsHitTestVisible = false
+                };
+                System.Windows.Controls.Canvas.SetLeft(circle, center.X - radius);
+                System.Windows.Controls.Canvas.SetTop(circle, center.Y - radius);
+                canvas.Children.Add(circle);
+                _whiteDetectOverlays.Add(circle);
+
+                // 45°直径标注线（从圆心向左上到右下）
+                double offset = radius * 0.707; // cos(45°) * radius
+                var diamLine = new System.Windows.Shapes.Line
+                {
+                    X1 = center.X - offset,
+                    Y1 = center.Y - offset,
+                    X2 = center.X + offset,
+                    Y2 = center.Y + offset,
+                    Stroke = System.Windows.Media.Brushes.Red,
+                    StrokeThickness = 1,
+                    IsHitTestVisible = false
+                };
+                canvas.Children.Add(diamLine);
+                _whiteDetectOverlays.Add(diamLine);
+
+                // 尺寸标注（在斜线右上方）
+                string label = sizeMm >= 1000 ? $"{sizeMm / 1000:F2} mm" : $"{sizeMm:F0} μm";
+                var text = new System.Windows.Controls.TextBlock
+                {
+                    Text = label,
+                    Foreground = System.Windows.Media.Brushes.Red,
+                    FontSize = 11,
+                    IsHitTestVisible = false
+                };
+                System.Windows.Controls.Canvas.SetLeft(text, center.X + offset + 3);
+                System.Windows.Controls.Canvas.SetTop(text, center.Y - offset - 14);
+                canvas.Children.Add(text);
+                _whiteDetectOverlays.Add(text);
+            }
+        }
+
+        private void ClearWhiteDetectOverlays(System.Windows.Controls.Canvas canvas)
+        {
+            foreach (var el in _whiteDetectOverlays)
+                canvas.Children.Remove(el);
+            _whiteDetectOverlays.Clear();
+        }
+
+        #endregion
+
         private static T FindChildByName<T>(DependencyObject parent, string name) where T : FrameworkElement
         {
             int count = VisualTreeHelper.GetChildrenCount(parent);