直方图将柱状图替换为面积图，优化密集数据显示效果，Y轴刻度自动取整支持 K/M 缩写，X 轴根据数据范围自动设置。

XP.Common/Controls/ImageHistogram/ChartRenderer.cs

@@ -13,7 +13,7 @@ namespace XP.Common.Controls.ImageHistogram
     internal sealed class ChartRenderer
     {
         private readonly RadCartesianChart _chart;
-        private readonly BarSeries _barSeries;
+        private readonly ScatterAreaSeries _areaSeries;
         private readonly LinearAxis _xAxis;
 
         /// <summary>
@@ -25,12 +25,12 @@ namespace XP.Common.Controls.ImageHistogram
         /// 构造函数，接收 RadCartesianChart 实例 | Constructor, receives RadCartesianChart instance
         /// </summary>
         /// <param name="chart">图表控件实例 | Chart control instance</param>
-        /// <param name="barSeries">柱状图系列 | Bar series</param>
+        /// <param name="areaSeries">面积图系列 | Area series</param>
         /// <param name="xAxis">X 轴 | X axis</param>
-        public ChartRenderer(RadCartesianChart chart, BarSeries barSeries, LinearAxis xAxis)
+        public ChartRenderer(RadCartesianChart chart, ScatterAreaSeries areaSeries, LinearAxis xAxis)
         {
             _chart = chart ?? throw new ArgumentNullException(nameof(chart));
-            _barSeries = barSeries ?? throw new ArgumentNullException(nameof(barSeries));
+            _areaSeries = areaSeries ?? throw new ArgumentNullException(nameof(areaSeries));
             _xAxis = xAxis ?? throw new ArgumentNullException(nameof(xAxis));
         }
 
@@ -64,6 +64,8 @@ namespace XP.Common.Controls.ImageHistogram
             // 设置 X 轴范围 | Set X axis range
             _xAxis.Minimum = 0;
             _xAxis.Maximum = xAxisMax;
+            // 根据范围自动设置刻度间隔（保持 4-5 个刻度）| Auto set major step based on range (keep 4-5 ticks)
+            _xAxis.MajorStep = xAxisMax <= 255 ? 64 : 16384;
 
             // 构建数据点 | Build data points
             var dataPoints = new List<HistogramDataPoint>();
@@ -103,7 +105,7 @@ namespace XP.Common.Controls.ImageHistogram
             }
 
             // 更新图表数据 | Update chart data
-            _barSeries.ItemsSource = dataPoints;
+            _areaSeries.ItemsSource = dataPoints;
 
             // 设置 Y 轴范围 | Set Y axis range
             UpdateYAxis(displayData, isLogarithmic);
@@ -114,7 +116,7 @@ namespace XP.Common.Controls.ImageHistogram
         /// </summary>
         public void Clear()
         {
-            _barSeries.ItemsSource = null;
+            _areaSeries.ItemsSource = null;
 
             // X 轴范围重置为 0-255 | Reset X axis range to 0-255
             _xAxis.Minimum = 0;
@@ -131,9 +133,9 @@ namespace XP.Common.Controls.ImageHistogram
         {
             get
             {
-                if (_barSeries.ItemsSource is ICollection<HistogramDataPoint> collection)
+                if (_areaSeries.ItemsSource is ICollection<HistogramDataPoint> collection)
                     return collection.Count;
-                if (_barSeries.ItemsSource is IEnumerable<HistogramDataPoint> enumerable)
+                if (_areaSeries.ItemsSource is IEnumerable<HistogramDataPoint> enumerable)
                     return enumerable.Count();
                 return 0;
             }
@@ -173,7 +175,48 @@ namespace XP.Common.Controls.ImageHistogram
             if (maxValue == 0)
                 maxValue = 1;
 
-            SetYAxisRange(0, maxValue, isLogarithmic);
+            // 计算取整的 MajorStep（约 4 个刻度，对齐到 K/M 整数倍）| Calculate rounded MajorStep (~4 ticks, aligned to K/M multiples)
+            if (_chart.VerticalAxis is LinearAxis linearAxis)
+            {
+                long rawStep = maxValue / 4;
+                long step = RoundStepToNice(rawStep);
+                if (step < 1) step = 1;
+                linearAxis.MajorStep = step;
+
+                // 将最大值向上取整到 step 的整数倍 | Round max up to multiple of step
+                long roundedMax = ((maxValue / step) + 1) * step;
+                SetYAxisRange(0, roundedMax, isLogarithmic);
+            }
+            else
+            {
+                SetYAxisRange(0, maxValue, isLogarithmic);
+            }
+        }
+
+        /// <summary>
+        /// 将步长取整为"好看"的数值（1, 2, 5 的倍数 × 10^n）| Round step to "nice" value (multiples of 1, 2, 5 × 10^n)
+        /// 例如：123456 → 100000，350000 → 500000，780000 → 1000000
+        /// </summary>
+        private static long RoundStepToNice(long rawStep)
+        {
+            if (rawStep <= 0) return 1;
+
+            // 找到数量级 | Find order of magnitude
+            double magnitude = Math.Pow(10, Math.Floor(Math.Log10(rawStep)));
+            double normalized = rawStep / magnitude;
+
+            // 取整到 1, 2, 5 中最近的 | Round to nearest of 1, 2, 5
+            double niceNormalized;
+            if (normalized <= 1.5)
+                niceNormalized = 1;
+            else if (normalized <= 3.5)
+                niceNormalized = 2;
+            else if (normalized <= 7.5)
+                niceNormalized = 5;
+            else
+                niceNormalized = 10;
+
+            return (long)(niceNormalized * magnitude);
         }
 
         /// <summary>