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接到新任務，用來監控3D打印機的攝像頭,需要對其進行控制。之前我沒有做過任何這方面的工作，很是撓頭。不過有腳本和開源兩個強大的工具，我也不是很害怕。
首先有人指明需要用到的庫是OpenCV。CV是指Computer vision, 從名字就能判斷這是專注于視頻處理的庫。很快我就找到了python的調用demo.并且成功的帶動了手邊的攝像頭。http://opencv.org/安裝后，就能在sources/samples/python/demo文件夾下面找到完整的demo程序。
不過這不能解決項目問題。我們的項目要求在.net環境下開發。所以很快，我就找到了成熟的.net平臺下OpenCV解決方案，名叫EMGU；
同樣的，EMGU也完整的demo例程。在EMGU3.1版本的安裝路徑下面\Solution\VS2013-2015文件夾中，就有攝像頭的驅動例子：實現攝像頭實時采樣，只需要幾行代碼:
...
private static Capture _cameraCapture;
...
void run(){
try
{
_cameraCapture = new Capture();
}
catch (Exception e)
{
MessageBox.Show(e.Message);
return;
}
Application.Idle += ProcessFrame;
...
void ProcessFrame(object sender, EventArgs e)
{
Mat frame = _cameraCapture.QueryFrame();
}通過Applicaiton.Idle+= ProcessFrame的加載事件，非常優雅的實現了攝像頭的驅動。
進一步，EMGU中有Websevice的例子。但是例子中傳輸的是一串字符串，采用的是net.tcp協議。我嘗試傳輸p_w_picpath,結果在旁邊電腦成功訪問了我的攝像頭，但是卡頓非常嚴重。（暫時分析不出來卡頓的原因）
host端代碼:
using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.ServiceModel;
using System.ServiceModel.Description;
using System.Text;
using Emgu.CV;
namespace Webservice_Host
{
class Program
{
static void Main(string[] args)
{
Uri uri = new Uri("net.tcp://localhost:8082/ImageService");
NetTcpBinding binding = new NetTcpBinding();
binding.Security.Mode = SecurityMode.None;
//WSHttpBinding binding = new WSHttpBinding();
binding.MaxReceivedMessageSize = 2147483647;
ServiceHost host = new ServiceHost(typeof(ImageService));
ServiceBehaviorAttribute serviceBehavior = host.Description.Behaviors.Find<ServiceBehaviorAttribute>();
serviceBehavior.IncludeExceptionDetailInFaults = true;
// Create endpoint
host.AddServiceEndpoint(typeof(IImageService), binding, uri);
host.Open();
Console.WriteLine("Service is ready, press any key to terminate.");
Console.ReadKey();
host.Close();
}
}
}ImageService.cs
using System;
using System.Collections.Generic;
using System.Text;
using System.ServiceModel;
using Emgu.CV;
using Emgu.CV.CvEnum;
using Emgu.CV.Structure;
namespace Webservice_Host
{
public class ImageService : IImageService
{
public Image<Bgr, Byte> GrabFrame()
{
Capture _capture = new Capture();
Mat frame=new Mat();
//_capture.Retrieve(frame,0);
//Image<Bgr, Byte> img = frame.ToImage<Bgr, Byte>();
Image<Bgr, Byte> img = _capture.QueryFrame().ToImage<Bgr, Byte>();
if (_capture != null)
_capture.Dispose();
return img;
}
}
}IImageService.cs
using System;
using System.Collections.Generic;
using System.Text;
using Emgu.CV;
using Emgu.CV.Structure;
using System.ServiceModel;
namespace Webservice_Host
{
[ServiceContract]
[XmlSerializerFormat]
public interface IImageService
{
[OperationContract(IsOneWay = false)]
Image<Bgr, Byte> GrabFrame();
}
}client端代碼：
//----------------------------------------------------------------------------
// Copyright (C) 2004-2016 by EMGU Corporation. All rights reserved.
//----------------------------------------------------------------------------
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.ServiceModel;
using System.Threading;
using Emgu.CV;
namespace Webservice_Client
{
public partial class Form1 : Form
{
private bool _started;
private Webservice_Host.IImageService _p_w_picpathGrabber;
private NetTcpBinding _binding;
private static Queue<IImage> p_w_picpathQ;
public Form1()
{
InitializeComponent();
_binding = new NetTcpBinding();
_binding.Security.Mode = SecurityMode.None;
_binding.MaxReceivedMessageSize = 2147483647;
Queue<IImage> p_w_picpathQ = new Queue<IImage>();
//System.Collections.Queue p_w_picpathQ= new System.Collections.Queue();
_started = false;
}
public bool Started
{
get { return _started; }
set
{
_started = value;
serviceUrlBox.Enabled = !_started;
if (!_started)
{
//stop grabing frames
//Application.Idle -= ProcessImage;
// System.Timers.Timer t =new System.Timers.Timer(1);
// t.Start();
// t.Elapsed+= ProcessImage;
}
else
{
//start to grab frames
_p_w_picpathGrabber = new ChannelFactory<Webservice_Host.IImageService>(
_binding,
new EndpointAddress(serviceUrlBox.Text)
).CreateChannel();
//System.Timers.Timer t =new System.Timers.Timer(50);
//t.Start();
////button2.Click += ProcessImage;
//t.Elapsed+= ProcessImage;
//// Application.Idle
Thread rx_p_w_picpath_thread = new Thread(new ThreadStart(get_p_w_picpath));
Thread show_p_w_picpath_thread = new Thread(new ThreadStart(show_p_w_picpath));
rx_p_w_picpath_thread.Start();
show_p_w_picpath_thread.Start();
}
}
}
private void get_p_w_picpath()
{
Queue<IImage> p_w_picpathQ = new Queue<IImage>();
while (true)
{
p_w_picpathQ.Enqueue(_p_w_picpathGrabber.GrabFrame());
}
}
private void show_p_w_picpath()
{
while (true) {
// if (p_w_picpathQ.Count>0&&p_w_picpathQ!=null)
// p_w_picpathBox1.Image=p_w_picpathQ.Dequeue();
}
}
private void ProcessImage(object sender, EventArgs e)
{
p_w_picpathBox1.Image = _p_w_picpathGrabber.GrabFrame();
}
private void button1_Click(object sender, EventArgs e)
{
Started = !Started;
if (Started == true)
button1.Text = "Stop";
else
button1.Text = "Start";
}
private void ReleaseResource()
{
Started = false;
}
private void button2_Click(object sender, EventArgs e)
{
}
}
}IImageService
using System;
using System.Collections.Generic;
using System.Text;
using Emgu.CV;
using Emgu.CV.Structure;
using System.ServiceModel;
namespace Webservice_Host
{
[ServiceContract]
[XmlSerializerFormat]
public interface IImageService
{
[OperationContract(IsOneWay = false)]
Image<Bgr, Byte> GrabFrame();
}
}到此為止，我對EMGU帶攝像頭的嘗試就結束了。后面我采用EMGU做了兩件事情，都是和網絡攝像頭有關：一是用ASP.NET用網頁控制遠程web攝像頭拍照并傳過來實時圖像。二是將EMGU截圖封裝成為dll的方法，交給其他工程師使用。
總體而言，也可能是受制于我的編程功力，無法用EMGU來實現更復雜的攝像頭訪問應用。但是EMGU作為OpenCV在.net平臺的封裝，其項目重心用在了圖像識別算法的封裝而不是多媒體應用上：我們可以看到大量的例程進行圖像識別等算法，調用起來非常方便。
而對于將攝像頭轉成流媒體源的工作，我找到了更加有效的框架，即微軟自帶的Media Foudation框架。
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