C#摄像头实现拍照功能的简单代码示例

using System;  
using System.Runtime.InteropServices;  
using System.Drawing;  
using System.Drawing.Imaging;  
namespace Video  
{  
///   
/// 一个C#摄像头控制类  
///   
public class VideoWork  
{  
private const int WM_USER = 0x400;  
private const int WS_CHILD = 0x40000000;  
private const int WS_VISIBLE = 0x10000000;  
private const int WM_CAP_START = WM_USER;  
private const int WM_CAP_STOP = WM_CAP_START + 68;  
private const int WM_CAP_DRIVER_CONNECT = WM_CAP_START + 10;  
private const int WM_CAP_DRIVER_DISCONNECT = WM_CAP_START + 11;  
private const int WM_CAP_S***EDIB = WM_CAP_START + 25;  
private const int WM_CAP_GRAB_FRAME = WM_CAP_START + 60;  
private const int WM_CAP_SEQUENCE = WM_CAP_START + 62;  
private const int WM_CAP_FILE_SET_CAPTURE_FILEA = WM_CAP_START + 20;  
private const int WM_CAP_SEQUENCE_NOFILE =WM_CAP_START+ 63;  
private const int WM_CAP_SET_OVERLAY =WM_CAP_START+ 51;   
private const int WM_CAP_SET_PREVIEW =WM_CAP_START+ 50;   
private const int WM_CAP_SET_CALLBACK_VIDEOSTREAM = WM_CAP_START +6;  
private const int WM_CAP_SET_CALLBACK_ERROR=WM_CAP_START +2;  
private const int WM_CAP_SET_CALLBACK_STATUSA= WM_CAP_START +3;  
private const int WM_CAP_SET_CALLBACK_FRAME= WM_CAP_START +5;  
private const int WM_CAP_SET_SCALE=WM_CAP_START+ 53;  
private const int WM_CAP_SET_PREVIEWRATE=WM_CAP_START+ 52;   
private IntPtr hWndC;  
private bool bWorkStart = false;  
private IntPtr mControlPtr;  
private int mWidth;  
private int mHeight;  
private int mLeft;  
private int mTop;  
 
///   
/// 初始化显示图像  
///   
/// 控件的句柄  
/// 开始显示的左边距  
/// 开始显示的上边距  
/// 要显示的宽度  
/// 要显示的长度  
public VideoWork(IntPtr handle, int left, int top, int width,int height)  
{  
mControlPtr = handle;  
mWidth = width;  
mHeight = height;  
mLeft = left;  
mTop = top;  
}  
[DllImport("avicap32.dll")]   
private static extern IntPtr capCreateCaptureWindowA(byte[] lpszWindowName, int dwStyle, int x, int y, int nWidth, int nHeight, IntPtr hWndParent, int nID);  
[DllImport("avicap32.dll")]  
private static extern int capGetVideoFormat(IntPtr hWnd, IntPtr psVideoFormat, int wSize );  
[DllImport("User32.dll")]   
private static extern bool SendMessage(IntPtr hWnd, int wMsg, int wParam, long lParam);  
///   
/// 开始显示图像  
///   
public void Start()  
{  
if (bWorkStart)  
return;  
bWorkStart = true;  
byte[] lpszName = new byte[100];  
hWndC = capCreateCaptureWindowA(lpszName,WS_CHILD|WS_VISIBLE ,mLeft,mTop,mWidth,mHeight,mControlPtr,0);  
if (hWndC.ToInt32() != 0)  
{  
SendMessage(hWndC, WM_CAP_SET_CALLBACK_VIDEOSTREAM, 0, 0);  
SendMessage(hWndC, WM_CAP_SET_CALLBACK_ERROR, 0, 0);  
SendMessage(hWndC, WM_CAP_SET_CALLBACK_STATUSA, 0, 0);  
SendMessage(hWndC, WM_CAP_DRIVER_CONNECT, 0, 0);  
SendMessage(hWndC, WM_CAP_SET_SCALE, 1, 0);  
SendMessage(hWndC, WM_CAP_SET_PREVIEWRATE, 66, 0);  
SendMessage(hWndC, WM_CAP_SET_OVERLAY, 1, 0);  
SendMessage(hWndC, WM_CAP_SET_PREVIEW, 1, 0);  
//Global.log.Write("SendMessage");  
}  
return;  
}  
///   
/// 停止显示  
///   
public void Stop()  
{  
SendMessage(hWndC, WM_CAP_DRIVER_DISCONNECT, 0, 0);  
bWorkStart = false;  
}  
///   
/// 抓图  
///   
/// 要保存bmp文件的路径  
public void GrabImage(string path)  
{  
IntPtr hBmp = Marshal.StringToHGlobalAnsi(path);  
SendMessage(hWndC,WM_CAP_S***EDIB,0,hBmp.ToInt64());  
}  
}  
}  
   
这是一个控制摄像头进行拍照的类，我每次使用GrabImage抓图都是225K的一张照片，我想请问如何才能让我抓到的图片小一些，我想控制在70K左右。不知怎么让拍照的像素变小？  
   
if(this.Request.QueryString["filename"]!=null)  
{  
                //获取原图片  
string filename=this.Request.QueryString["filename"];  
Bitmap bmpOld=new Bitmap(this.Server.MapPath("images/" + filename));  
    //计算缩小比例  
double d1;  
if(bmpOld.Height>bmpOld.Width)  
d1=(double)(MaxLength/(double)bmpOld.Width);  
else 
d1=(double)(MaxLength/(double)bmpOld.Height);  
//产生缩图  
Bitmap bmpThumb=new Bitmap(bmpOld,(int)(bmpOld.Width*d1),(int)(bmpOld.Height*d1));  
//清除缓冲  
Response.Clear();  
//生成图片  
bmpThumb.Save(this.Response.OutputStream,ImageFormat.Jpeg);  
Response.End();  
//释放资源  
bmpThumb.Dispose();  
bmpOld.Dispose();  
}