为什么trackBar2.最大显示16步，而不是15步

位图是数组，包含从0到14的15个索引。但在设置trackBar2.最大位图长度后，我在trackBar2上看到的是16位而不是15位。

private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            trackBar2.Enabled = true;
            trackBar2.Maximum = bitmaps.Length;
            for (int i = 0; i < bitmaps.Length; i++)
            {
               ConvertTo24(bitmaps[i]);
            }
            timer2.Stop();
            b1.Dispose();
        }

然后在trackBar2滚动事件中：

private void trackBar2_Scroll(object sender, EventArgs e)
        {
            LoadPictureAt(trackBar2.Value, sender);
            mymem = ToStream(bitmaps[trackBar2.Value], ImageFormat.Bmp);
            backTexture = TextureLoader.FromStream(D3Ddev, mymem);
            scannedCloudsTexture = new Texture(D3Ddev, 512, 512, 1, Usage.Dynamic, Format.A8R8G8B8, Pool.Default);
            timer1.Stop();
            Button1Code();
            timer1.Start();
            pictureBox1.Refresh();
        }

当我把scrollBar2移到顶部时，它抛出了异常：Index在数组的边界之外

System.IndexOutOfRangeException was caught
  HResult=-2146233080
  Message=Index was outside the bounds of the array.
  Source=My Weather Station
  StackTrace:
       at mws.ScanningClouds.trackBar2_Scroll(Object sender, EventArgs e) in d:'C-Sharp'Download File'Downloading-File-Project-Version-012'Downloading File'ScanningClouds.cs:line 709
       at System.Windows.Forms.TrackBar.OnScroll(EventArgs e)
       at System.Windows.Forms.TrackBar.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.SendMessage(HandleRef hWnd, Int32 msg, IntPtr wParam, IntPtr lParam)
       at System.Windows.Forms.Control.SendMessage(Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.Control.ReflectMessageInternal(IntPtr hWnd, Message& m)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ScrollableControl.WmVScroll(Message& m)
       at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
       at System.Windows.Forms.Form.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.CallWindowProc(IntPtr wndProc, IntPtr hWnd, Int32 msg, IntPtr wParam, IntPtr lParam)
       at System.Windows.Forms.NativeWindow.DefWndProc(Message& m)
       at System.Windows.Forms.Control.DefWndProc(Message& m)
       at System.Windows.Forms.Control.WmMouseMove(Message& m)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.TrackBar.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(Form mainForm)
       at mws.Program.Main() in d:'C-Sharp'Download File'Downloading-File-Project-Version-012'Downloading File'Program.cs:line 28
  InnerException: 

709行为：

mymem = ToStream(bitmaps[trackBar2.Value], ImageFormat.Bmp);

trackBar2最小值被设置为0，我试图将其设置为1，但随后我在同一行上得到了异常。同样的异常，即使现在trackBar2有15个步骤，当我将trackBar2滚动条从顶部拖到最后时，仍然是同样的异常。