OpenCV学习笔记（5）在单个窗口中显示多个视频子窗口

参考OpenCV中文论坛的一个帖子（http://www.opencv.org.cn/forum/viewtopic.php?f=1&t=7996&start=0）实现了在一个窗口显示多个视频子窗口，能够读入单个的视频或摄像头数据，然后在一个窗口中分别显示原始帧图像、反色图像、灰度图像以及Canny边缘检测图像。并在每个子窗口左上角显示系统时间，函数cvShowManyImages是改写的。

代码如下：

#include "stdafx.h"
#include <cv.h>
#include <cxcore.h>
#include <highgui.h>

#include <stdio.h>
#include <stdarg.h>
#include <time.h>

// 隐藏 console 窗口
#pragma comment( linker, "/subsystem:/"windows/" /entry:/"mainCRTStartup/"" )

// 单窗口显示多幅图像的函数
void cvShowMultiImages(char* title, int nArgs, ...) 
{

   // img - Used for getting the arguments 
   IplImage* img;

   // DispImage - the image in which all the input images are to be copied
   IplImage* DispImage;

   int size;    // size - the size of the images in the window
   int ind;        // ind - the index of the image shown in the window
   int x, y;    // x,y - the coordinate of top left coner of input images
   int w, h;    // w,h - the width and height of the image

   // r - Maximum number of images in a column 
   // c - Maximum number of images in a row 
   int r, c;

   // scale - How much we have to resize the image
   float scale;
   // max - Max value of the width and height of the image
   int max;
   // space - the spacing between images
   int space;

   // If the number of arguments is lesser than 0 or greater than 12
   // return without displaying 
   if(nArgs <= 0) {
      printf("Number of arguments too small..../n");
      return;
   }
   else if(nArgs > 12) {
      printf("Number of arguments too large..../n");
      return;
   }
   // Determine the size of the image, 
   // and the number of rows/cols 
   // from number of arguments 
   else if (nArgs == 1) {
      r = c = 1;
      size = 300;
   }
   else if (nArgs == 2) {
      r = 2; c = 1;
      size = 300;
   }
   else if (nArgs == 3 || nArgs == 4) {
      r = 2; c = 2;
      size = 300;
   }
   else if (nArgs == 5 || nArgs == 6) {
      r = 3; c = 2;
      size = 200;
   }
   else if (nArgs == 7 || nArgs == 8) {
      r = 4; c = 2;
      size = 200;
   }
   else {
      r = 4; c = 3;
      size = 150;
   }

   // Create a new 3 channel image to show all the input images
   DispImage = cvCreateImage( cvSize(60 + size*r, 20 + size*c), IPL_DEPTH_8U, 3 );

   // Used to get the arguments passed
   va_list args;
   va_start(args, nArgs);

   // Loop for nArgs number of arguments
   space = 20;
   for (ind = 0, x = space, y = space; ind < nArgs; ind++, x += (space + size)) {

      // Get the Pointer to the IplImage
      img = va_arg(args, IplImage*);

      // Check whether it is NULL or not
      // If it is NULL, release the image, and return
      if(img == 0) {
         printf("Invalid arguments");
         cvReleaseImage(&DispImage);
         return;
      }

      // Find the width and height of the image
      w = img->width;
      h = img->height;

      // Find whether height or width is greater in order to resize the image
      max = (w > h)? w: h;

      // Find the scaling factor to resize the image
      scale = (float) ( (float) max / size );

      // Used to Align the images
      // i.e. Align the image to next row
      if( ind % r == 0 && x!= space) {
         x  = space;
         y += space + size;
      }

      // Set the image ROI to display the current image
      cvSetImageROI(DispImage, cvRect(x, y, (int)( w/scale ), (int)( h/scale )));

      // Resize the input image and copy the it to the Single Big Image
      cvResize(img, DispImage);

      // Reset the ROI in order to display the next image
      cvResetImageROI(DispImage);
   }

   // Create a new window, and show the Single Big Image
   //cvNamedWindow( title, 1 );
   cvShowImage( title, DispImage);


   // End the number of arguments
   va_end(args);

   // Release the Image Memory
   cvReleaseImage(&DispImage);
}


int main( int argc, char** argv ) 
{
   CvCapture* capture;   
   
   if (argc == 1)
   {
      capture = cvCreateCameraCapture( 0 );
   }
   else
   {
      capture = cvCreateFileCapture( argv[1] );      
   }
   
   IplImage* frame;
   
   cvNamedWindow("video",1);
   cvResizeWindow("video",750,750);
   
   CvFont timeFont,timeFont1;
   cvInitFont(&timeFont,  CV_FONT_HERSHEY_COMPLEX, 1.0f,1.0f,0,1,8);
   cvInitFont(&timeFont1, CV_FONT_HERSHEY_COMPLEX, 1.0f,1.0f,0,1,8);
   
   // Initialize new applied memory of 'time1'
   char timestr[25];
   memset(timestr, 0, 25 * sizeof(char));
   
   while (1)
   {
      frame = cvQueryFrame( capture );
      if (!frame) break;
         
      // Get the systme local time info
      time_t rawtime; 
      struct tm* timeinfo; 
      //time( &rawtime ); 

      rawtime = time( NULL ); 
      timeinfo = localtime( &rawtime ); 
      char* p = asctime( timeinfo );
      
      // the 25th character of array 'p' is '/n'
      // but it can not be display correctly in the image
      // so we just read out the first 24 character of 'p'
      for (int i = 0; i < 24; i++)
      {
         timestr[i] = *p;
         p++;
      }
      p = NULL;
      
      // Bitwise inversion of every element of the current frame
      IplImage* frame_not = cvCreateImage(cvGetSize(frame),frame->depth,frame->nChannels);
      cvNot(frame,frame_not);
      
      // Get the gray scale image of the current frmae
      // and transform the gray image from single channel to three channels
      IplImage* frame_gray=cvCreateImage(cvGetSize(frame),frame->depth,1);
      IplImage* frame1=cvCreateImage(cvGetSize(frame),frame->depth,frame->nChannels);
      cvCvtColor(frame,frame_gray,CV_RGB2GRAY);
      cvCvtColor(frame_gray,frame1,CV_GRAY2BGR);
      
      // Do Canny edge detection
      // and transform the result image from single channel to three channels
      IplImage* frame_canny=cvCreateImage(cvGetSize(frame),frame->depth,1);
      IplImage* frame2=cvCreateImage(cvGetSize(frame),frame->depth,frame->nChannels);
      cvCanny(frame_gray,frame_canny,20,75,3);
      cvCvtColor(frame_canny,frame2,CV_GRAY2BGR);

      // Display the local time information in each image
      cvPutText( frame,        timestr, cvPoint(5,25), &timeFont,  CV_RGB(255,0,0) );
      cvPutText( frame1,    timestr, cvPoint(5,25), &timeFont,  CV_RGB(255,0,0) );
      cvPutText( frame2,    timestr, cvPoint(5,25), &timeFont1, CV_RGB(255,0,0) );
      cvPutText( frame_not, timestr, cvPoint(5,25), &timeFont1, CV_RGB(255,0,0) );

      cvShowMultiImages("video",4,frame,frame_not,frame1,frame2);

      
      //cvWaitKey(33);
      int key = cvWaitKey(33);
      if( key == 27 ) break;

      cvReleaseImage(&frame_not);
      cvReleaseImage(&frame1);
      cvReleaseImage(&frame_gray);
      cvReleaseImage(&frame2);
      cvReleaseImage(&frame_canny);   

   }
   
   cvDestroyWindow("video");
   cvReleaseCapture(&capture);

   return 0;

}

有几点需要注意：
1、在 while 循环中，处理完的图像应及时释放所占用的内存（cvReleaseImage），否则会不断占用内存空间以致系统当机。
2、图像数据的指针若是由 cvCreateImage 返回的，则应由 cvReleaseImage 来释放内存；如果是读取自视频或摄像头的帧图像，则应用 cvReleaseCapture 来释放内存，不必再用 cvReleaseImage() ，在 while 循环中使用 cvReleaseImage( &frame )  会导致生成的程序在执行时出错。
3、有关va_list、va_start、va_arg、va_end的原理与使用，参见 http://www.cppblog.com/qiujian5628/archive/2008/01/21/41562.html