EmguCV Image Process: Process Video Sequences part 3

EmguCV Image Process: Process Video Sequences

參考OpenCV 2 Computer Vision Application Programming Cookbook第十章

介紹內容如下：

Reading video sequences

Processing the video frames

Writing video sequences

Tracking feature points in video

Extracting the foreground objects in video

承接上一篇所介紹的內容

一樣透過VideoProcessor這個類別

加入把處理過的影像寫檔的功能

在這個類別中加入以下這些欄位

//The OpenCV video witer object
VideoWriter writer;
//output filename
string outputFile;
//current index for output images
int currentIndex;
//number of digits in output image filename
int digits;
//extension of output images
string extension;

這裡新增一個VideoWriter的類別

這就是EmguCV用來寫檔的類別

其他欄位像是儲存寫檔的檔名

儲存成影像檔的index、副檔名等等

接著加入以下的方法

/// <summary>
/// set the output video file by default the same 
/// parameters than input video will be used
/// </summary>
/// <param name="filename">file name</param>
/// <param name="codec">video codec</param>
/// <param name="framerate">video FPS</param>
/// <param name="isColor">is color</param>
/// <returns>success or fail</returns>
public bool SetOutput(string filename, bool isColor)
{
    double framerate = GetFrameRate();//same as input
    Size size = GetFrameSize();

    this.outputFile = filename;
    this.extension = string.Empty;

    this.writer = new VideoWriter(this.outputFile, GetCodec(), (int)framerate, size.Width, size.Height, isColor);
    return true;
}

/// <summary>
/// set output as a series of image files
/// extension must be ".jpg", ".bmp" ...
/// </summary>
/// <param name="filename">prefix</param>
/// <param name="ext">image file extension</param>
/// <param name="numberOfDigits">number of digits</param>
/// <param name="startIndex">start index</param>
/// <returns>success or fail</returns>
public bool SetOutput(string filename, string ext)
{
    //filenames and their common extension
    this.outputFile = filename;
    this.extension = ext;
    //number of digits in the file numbering scheme
    this.digits = 3;
    //start numbering at this index
    this.currentIndex = 0;

    return true;
}

/// <summary>
/// Get the codec of input video 
/// </summary>
/// <returns>the codec</returns>
private int GetCodec()
{
    return CvInvoke.CV_FOURCC('X', 'V', 'I', 'D');
}

/// <summary>
/// Get the frame size of input video
/// </summary>
/// <returns>the frame size</returns>
private Size GetFrameSize()
{
    Size size = new Size()
    {
        Height = this.capture.Height,
        Width =this.capture.Width
    };
    return size;
}

/// <summary>
/// to write the output frame
/// could be video or image
/// </summary>
/// <param name="frame">output frame</param>
private void WriteNextFrame(IImage frame)
{
    if (!string.IsNullOrWhiteSpace(this.extension))
    {
        string imageFile = this.outputFile + this.currentIndex + this.extension;
        this.currentIndex++;
        frame.Save(imageFile);
    }
    else
    {
        if (frame.NumberOfChannels == 1)
        {
            this.writer.WriteFrame((Image<Gray, Byte>)frame);
        }
        else
        {
            this.writer.WriteFrame((Image<Bgr, Byte>)frame);
        }
    }

}

這裡分別加入兩個設定output的方法

採用多載的方式(相同名稱的方法SetOutput)

一個做為output為video的設定

一個做為output為image的設定

而output為video的部分

要取得codec，因此加入一個GetCodec的方法

這裡採用一般電腦都會有安裝的XVID這個codec

然後GetFrameSize取得capture所擷取的影像的大小

WriteNextFrame就判斷是要出輸出video還是image

然後在原本的Run這個方法中

加入寫檔的操作

/// <summary>
/// to grab (and process) the frame of the sequence
/// </summary>
public void Run()
{
    //current frame
    IImage frame;
    //output frame
    IImage output;
    //if no catpure device has been set
    if (!this.IsOpened)
    {
        return;
    }

    this.stop = false;
    while (!IsStopped)
    {
        //read next frame if any
        frame = this.capture.QueryFrame();
        if (frame == null)
        {
            break;
        }
        //display input frame
        if(!string.IsNullOrWhiteSpace(this.windowNameInput))
        {
            CvInvoke.cvShowImage(this.windowNameInput, frame.Ptr);
        }
        //calling the process function
        if (this.callIt)
        {
            //process the frame
            output = process(frame);
            //increment frame number
            this.fnumber++;
        }
        else
        {
            output = frame;
        }

        //write output sequence
        if (!string.IsNullOrWhiteSpace(this.outputFile))
        {
            WriteNextFrame(output);
        }

        //display output frame
        if (!string.IsNullOrWhiteSpace(this.windowNameOutput))
        {
            CvInvoke.cvShowImage(this.windowNameOutput, output.Ptr);
        }
        //introduce a delay
        if (this.delay >= 0 && CvInvoke.cvWaitKey(delay) >= 0)
        {
            StopIt();
        }
        //check if we should stop
        if (this.frameToStop >= 0 && GetFrameNumber() == this.frameToStop)
        {
            StopIt();
        }

    }
    this.writer.Dispose();
}

在output接收到處理過的frame後

判斷outputFile是否有值，有的話則進行WriteNextFrame的動作

並把處理後的frame(output)帶入即可


操作的方式也很簡單

如下

//Create instance
VideoProcessor processor = new VideoProcessor();
//Open the video file
processor.SetInput(@"E:\2012 Taipei Time Lapse.mov");
processor.SetFrameProcessor(Canny);
processor.SetOutput(@"E:\output.avi", false);
//processor.SetOutput(@"E:\output\output", ".jpg");
//Start the process
processor.Run();    

執行後就會開始讀取E:\2012 Taipei Time Lapse.mov這個影片檔

並且把這個檔案寫入E:\output.avi

若是下面那行註解的就是將影像一張一張存入E:\output\資料夾中

結果如下

這是存成圖片的結果

 這是轉錄成影片，由media player播放的開頭

 這是轉錄成影片，由media player播放的龍山寺

這是轉錄成影片，由media player播放的國父紀念館


接著下一篇將會介紹如何去追蹤影片中的特徵值(feature)