Почему я получаю OutOfMemoryException, даже если я выпускаю / удаляю растровое изображение?

У меня есть этот класс, где я использую код для создания скриншотов:

using System;
using System.Runtime.InteropServices;
using System.Drawing;
using System.Drawing.Imaging;

namespace WindowsFormsApplication1
{
    /// <summary>
    /// Provides functions to capture the entire screen, or a particular window, and save it to a file.
    /// </summary>
    public class ScreenCapture
    {
        /// <summary>
        /// Creates an Image object containing a screen shot of the entire desktop
        /// </summary>
        /// <returns></returns>
        public Image CaptureScreen()
        {
            return CaptureWindow(User32.GetDesktopWindow());
        }

        /// <summary>
        /// Creates an Image object containing a screen shot of a specific window
        /// </summary>
        /// <param name="handle">The handle to the window. (In windows forms, this is obtained by the Handle property)</param>
        /// <returns></returns>
        public Image CaptureWindow(IntPtr handle)
        {
            // get te hDC of the target window
            IntPtr hdcSrc = User32.GetWindowDC(handle);
            // get the size
            User32.RECT windowRect = new User32.RECT();
            User32.GetWindowRect(handle, ref windowRect);
            int width = windowRect.right - windowRect.left;
            int height = windowRect.bottom - windowRect.top;
            // create a device context we can copy to
            IntPtr hdcDest = GDI32.CreateCompatibleDC(hdcSrc);
            // create a bitmap we can copy it to,
            // using GetDeviceCaps to get the width/height
            IntPtr hBitmap = GDI32.CreateCompatibleBitmap(hdcSrc, width, height);
            // select the bitmap object
            IntPtr hOld = GDI32.SelectObject(hdcDest, hBitmap);
            // bitblt over
            GDI32.BitBlt(hdcDest, 0, 0, width, height, hdcSrc, 0, 0, GDI32.SRCCOPY);
            // restore selection
            GDI32.SelectObject(hdcDest, hOld);
            // clean up 
            GDI32.DeleteDC(hdcDest);
            User32.ReleaseDC(handle, hdcSrc);

            // get a .NET image object for it
            Image img = Image.FromHbitmap(hBitmap);
            // free up the Bitmap object
            GDI32.DeleteObject(hBitmap);

            return img;
        }

        /// <summary>
        /// Captures a screen shot of a specific window, and saves it to a file
        /// </summary>
        /// <param name="handle"></param>
        /// <param name="filename"></param>
        /// <param name="format"></param>
        public void CaptureWindowToFile(IntPtr handle, string filename, ImageFormat format)
        {
            using (Image img = CaptureWindow(handle))
            {
                img.Save(filename, format);
            }
        }

        /// <summary>
        /// Captures a screen shot of the entire desktop, and saves it to a file
        /// </summary>
        /// <param name="filename"></param>
        /// <param name="format"></param>
        public void CaptureScreenToFile(string filename, ImageFormat format)
        {
            using (Image img = CaptureScreen())
            {
                img.Save(filename, format);
            }
        }

        /// <summary>
        /// Helper class containing Gdi32 API functions
        /// </summary>
        private class GDI32
        {

            public const int SRCCOPY = 0x00CC0020; // BitBlt dwRop parameter

            [DllImport("gdi32.dll")]
            public static extern bool BitBlt(IntPtr hObject, int nXDest, int nYDest,
                int nWidth, int nHeight, IntPtr hObjectSource,
                int nXSrc, int nYSrc, int dwRop);
            [DllImport("gdi32.dll")]
            public static extern IntPtr CreateCompatibleBitmap(IntPtr hDC, int nWidth,
                int nHeight);
            [DllImport("gdi32.dll")]
            public static extern IntPtr CreateCompatibleDC(IntPtr hDC);
            [DllImport("gdi32.dll")]
            public static extern bool DeleteDC(IntPtr hDC);
            [DllImport("gdi32.dll")]
            public static extern bool DeleteObject(IntPtr hObject);
            [DllImport("gdi32.dll")]
            public static extern IntPtr SelectObject(IntPtr hDC, IntPtr hObject);
        }

        /// <summary>
        /// Helper class containing User32 API functions
        /// </summary>
        private class User32
        {
            [StructLayout(LayoutKind.Sequential)]
            public struct RECT
            {
                public int left;
                public int top;
                public int right;
                public int bottom;
            }

            [DllImport("user32.dll")]
            public static extern IntPtr GetDesktopWindow();
            [DllImport("user32.dll")]
            public static extern IntPtr GetWindowDC(IntPtr hWnd);
            [DllImport("user32.dll")]
            public static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDC);
            [DllImport("user32.dll")]
            public static extern IntPtr GetWindowRect(IntPtr hWnd, ref RECT rect);

        }


    }
}

Затем у меня есть новый класс, который я создал, когда я использую AviFile для создания файлов AVI-фильмов со скриншотов в режиме реального времени:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using AviFile;
using System.Drawing;


namespace WindowsFormsApplication1
{
    class ScreenshotsToAvi
    {
        int count = 0;
        VideoStream aviStream;
        AviManager aviManager;
        Bitmap bmp;

        public ScreenshotsToAvi()
        {
            aviManager = new AviManager(@"d:\testdata\new.avi", false);
        }

        public void CreateAvi(ScreenCapture sc)
        {
            bmp = new Bitmap(sc.CaptureScreen());
            count++;
            if (count == 1)
            {
                aviStream = aviManager.AddVideoStream(false, 25, bmp);
            }
            aviStream.AddFrame(bmp);
            bmp.Dispose();
        }

        public AviManager avim
        {
            get
            {
                return aviManager;
            }
            set
            {
                aviManager = value;
            }
        }
    }
}

Затем в форме я использую его следующим образом:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        ScreenshotsToAvi screens2avi;
        int count;
        ScreenCapture sc;

        public Form1()
        {
            InitializeComponent();

            screens2avi = new ScreenshotsToAvi();
            label2.Text = "0";
            count = 0;
            sc = new ScreenCapture();

        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            count++;
            sc.CaptureScreen();
            screens2avi.CreateAvi(this.sc);
            label2.Text = count.ToString();

        }

        private void button1_Click(object sender, EventArgs e)
        {
            timer1.Enabled = true;
        }

        private void button2_Click(object sender, EventArgs e)
        {
            timer1.Enabled = false;
            screens2avi.avim.Close();
        }

        private void button3_Click(object sender, EventArgs e)
        {
            timer1.Enabled = false;
            string[] filePaths = Directory.GetFiles(@"c:\temp\screens7\");
            foreach (string filePath in filePaths)
                File.Delete(filePath);
            label2.Text = "0";
        }
    }
}

После того, как я запускаю программу около минуты или двух, она попадает в класс ScreenShotsToAvi и в этой строке генерирует исключение:

bmp = new Bitmap(sc.CaptureScreen());

Недостаточно памяти

System.OutOfMemoryException was unhandled
  HResult=-2147024882
  Message=Out of memory.
  Source=System.Drawing
  StackTrace:
       at System.Drawing.Graphics.CheckErrorStatus(Int32 status)
       at System.Drawing.Graphics.DrawImage(Image image, Int32 x, Int32 y, Int32 width, Int32 height)
       at System.Drawing.Bitmap..ctor(Image original, Int32 width, Int32 height)
       at System.Drawing.Bitmap..ctor(Image original)
       at WindowsFormsApplication1.ScreenshotsToAvi.CreateAvi(ScreenCapture sc) in d:\C-Sharp\ReadWriteToMemory\WindowsFormsApplication1\WindowsFormsApplication1\ScreenshotsToAvi.cs:line 26
       at WindowsFormsApplication1.Form1.timer1_Tick(Object sender, EventArgs e) in d:\C-Sharp\ReadWriteToMemory\WindowsFormsApplication1\WindowsFormsApplication1\Form1.cs:line 41
       at System.Windows.Forms.Timer.OnTick(EventArgs e)
       at System.Windows.Forms.Timer.TimerNativeWindow.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 WindowsFormsApplication1.Program.Main() in d:\C-Sharp\ReadWriteToMemory\WindowsFormsApplication1\WindowsFormsApplication1\Program.cs:line 19
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: 

И снова im избавляя bmp все время, так почему исключение подходит? Нужно ли мне все же распоряжаться?

public void CreateAvi(ScreenCapture sc)
        {
            bmp = new Bitmap(sc.CaptureScreen());
            count++;
            if (count == 1)
            {
                aviStream = aviManager.AddVideoStream(false, 25, bmp);
            }
            aviStream.AddFrame(bmp);
            bmp.Dispose();
        }