.NET TWAIN image scanner

GC.Finalize() 

bool IMessageFilter.PreFilterMessage( ref Message m )
		    {
		    TwainCommand cmd = tw.PassMessage( ref m );
		    if( cmd == TwainCommand.Not )
			    return false;
 
		    switch( cmd )
			    {
			    case TwainCommand.CloseRequest:
				    {
				    EndingScan();
				    tw.CloseSrc();
				    break;
				    }
			    case TwainCommand.CloseOk:
				    {
				    EndingScan();
				    tw.CloseSrc();
				    break;
				    }
			    case TwainCommand.DeviceEvent:
				    {
				    break;
				    }
			    case TwainCommand.TransferReady:
				    {
				    ArrayList pics = tw.TransferPictures();
				    EndingScan();
				    tw.CloseSrc();
				    picnumber++;
                    MessageBox.Show("Number of Scanned Docs: " + pics.Count.ToString());
				    for( int i = 0; i < pics.Count; i++ )
					    {
					    IntPtr img = (IntPtr) pics[ i ];
                        //PicForm newpic = new PicForm( img );
                        //newpic.MdiParent = this;
					    //int picnum = i + 1;
                        this.pictureBox1.Image = TwainHelper.ImageFromIntPtr(img);
                        //newpic.Text = "ScanPass" + picnumber.ToString() + "_Pic" + picnum.ToString();
                        //newpic.Show();
					    }
				    break;
				    }
			    }
 
		    return true;
		    }
----------------------------------------
using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Drawing;
using System.Drawing.Imaging;
using System.Reflection;
 
namespace TwainGui
{
    [StructLayout(LayoutKind.Sequential, Pack = 1)]
    public class BITMAPINFOHEADER
    {
        public uint biSize;
        public int biWidth;
        public int biHeight;
        public ushort biPlanes;
        public ushort biBitCount;
        public uint biCompression;
        public uint biSizeImage;
        public int biXPelsPerMeter;
        public int biYPelsPerMeter;
        public uint biClrUsed;
        public uint biClrImportant;
        public void Init() { this.biSize = (uint)Marshal.SizeOf(this); }
    }
    class TwainHelper
    {
        private static ImageCodecInfo GetEncoderInfo(String mimeType)
        {
            ImageCodecInfo[] encoders = ImageCodecInfo.GetImageEncoders();
            for (int j = 0; j < encoders.Length; ++j)
            {
                if (encoders[j].MimeType == mimeType)
                    return encoders[j];
            }
            return null;
        }
 

        public static Image ImageFromIntPtr(IntPtr imagePtr)
        {
            BITMAPINFOHEADER bmpInfoHeader = new BITMAPINFOHEADER();
            IntPtr bmpptr = GlobalLock(imagePtr);
            IntPtr pixptr = GetPixelInfo(bmpptr, bmpInfoHeader);
 
            Bitmap bitmap = new Bitmap(bmpInfoHeader.biWidth, bmpInfoHeader.biHeight);
            Graphics graphics = Graphics.FromImage(bitmap);
 
            IntPtr hdc = graphics.GetHdc();
            SetDIBitsToDevice(hdc, 0, 0, bmpInfoHeader.biWidth, bmpInfoHeader.biHeight,
                    0, 0, 0, bmpInfoHeader.biHeight, pixptr, bmpptr, 0);
            graphics.ReleaseHdc(hdc);
 
            return (Image)bitmap;
        }
 
        private static IntPtr GetPixelInfo(IntPtr bmpptr, BITMAPINFOHEADER bmpInfoHeader)
        {
            Marshal.PtrToStructure(bmpptr, bmpInfoHeader);
 
            if (bmpInfoHeader.biSizeImage == 0)
                bmpInfoHeader.biSizeImage = (uint)(((((uint)bmpInfoHeader.biWidth * (uint)bmpInfoHeader.biBitCount) + 31) & ~31) >> 3) * (uint)bmpInfoHeader.biHeight;
 
            int p = (int)bmpInfoHeader.biClrUsed;
            if ((p == 0) && (bmpInfoHeader.biBitCount <= 8))
                p = 1 << bmpInfoHeader.biBitCount;
            p = (p * 4) + (int)bmpInfoHeader.biSize + (int)bmpptr;
            return (IntPtr)p;
        }
        [DllImport("gdi32.dll", ExactSpelling = true)]
        internal static extern int SetDIBitsToDevice(IntPtr hdc, int xdst, int ydst,
                                                int width, int height, int xsrc, int ysrc, int start, int lines,
                                                IntPtr bitsptr, IntPtr bmiptr, int color);
        [DllImport("kernel32.dll", ExactSpelling = true)]
        internal static extern IntPtr GlobalLock(IntPtr handle);
        [DllImport("gdiplus.dll", ExactSpelling = true)]
        internal static extern int GdipCreateBitmapFromGdiDib(IntPtr bminfo, IntPtr pixdat, out IntPtr image);
 

    }
}