探测器设置界面增加图像灰度直方图，用于显示实时采集图像的灰度信息，优化图像灰度直方图的显示方式（无图像提示）和优化资源释放。

XP.Common/Controls/ImageHistogram/ImageHistogramControl.xaml.cs

@@ -219,10 +219,24 @@ namespace XP.Common.Controls.ImageHistogram
                 // 取消帧率限流器中的待处理任务 | Cancel pending tasks in throttler
                 _frameThrottler.Cancel();
 
-                // 清空图表 | Clear chart
-                if (_chartRenderer != null)
+                // 清空图表（捕获局部引用避免异步执行时为 null）| Clear chart (capture local ref to avoid null during async)
+                var renderer = _chartRenderer;
+                if (renderer != null)
                 {
-                    Dispatcher.InvokeAsync(() => _chartRenderer.Clear());
+                    Dispatcher.InvokeAsync(() =>
+                    {
+                        try
+                        {
+                            renderer.Clear();
+
+                            // 显示无数据提示 | Show no-data placeholder
+                            NoDataPlaceholder.Visibility = Visibility.Visible;
+                        }
+                        catch
+                        {
+                            // 控件已卸载时忽略 | Ignore if control already unloaded
+                        }
+                    });
                 }
             }
             catch (Exception ex)
@@ -259,6 +273,9 @@ namespace XP.Common.Controls.ImageHistogram
                                 {
                                     isLog = IsLogarithmic;
                                     _chartRenderer?.UpdateData(histogram, isLog);
+
+                                    // 隐藏无数据提示 | Hide no-data placeholder
+                                    NoDataPlaceholder.Visibility = Visibility.Collapsed;
                                 }
                                 catch (Exception ex)
                                 {