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changedetection.cc
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// Example : simple change detection from video / camera
// usage: prog {<video_name>}
// Author : Toby Breckon, [email protected]
// Copyright (c) 2008 School of Engineering, Cranfield University
// License : LGPL - http://www.gnu.org/licenses/lgpl.html
#include "cv.h" // opencv general include file
#include "highgui.h" // opencv GUI include file
#include "cvaux.h" // opencv aux functions include file
#include <stdio.h>
#include <algorithm> // contains max() function (amongst others)
using namespace cv; // use c++ namespace so the timing stuff works consistently
/******************************************************************************/
// setup the cameras properly based on OS platform
// 0 in linux gives first camera for v4l
//-1 in windows gives first device or user dialog selection
#ifdef linux
#define CAMERA_INDEX 0
#else
#define CAMERA_INDEX -1
#endif
/******************************************************************************/
int main( int argc, char** argv )
{
IplImage* img = NULL; // image object
IplImage* prev = NULL; // previous image object
IplImage* diff = NULL; // difference image object
CvCapture* capture = NULL; // capture object
char const * windowNameBG = "Original Scene"; // window name
char const * windowNameFG = "Scene Change"; // window name
bool keepProcessing = true; // loop control flag
char key; // user input
int EVENT_LOOP_DELAY = 40; // delay for GUI window
// 40 ms equates to 1000ms/25fps = 40ms per frame
// if command line arguments are provided try to read image/video_name
// otherwise default to capture from attached H/W camera
if(
( argc == 2 && (capture = cvCreateFileCapture( argv[1] )) != 0 ) ||
( argc != 2 && (capture = cvCreateCameraCapture( CAMERA_INDEX )) != 0 )
)
{
// create window object (use flag=0 to allow resize, 1 to auto fix size)
cvNamedWindow(windowNameFG, 0);
cvNamedWindow(windowNameBG, 0);
// if using a capture object we need to get a frame first to get the size
if (capture) {
// cvQueryFrame s just a combination of cvGrabFrame
// and cvRetrieveFrame in one call.
img = cvQueryFrame(capture);
if(!img){
if (argc == 2){
printf("End of video file reached\n");
} else {
printf("ERROR: cannot get next fram from camera\n");
}
exit(0);
}
}
// make copy of initial image frame and setup memory image objects
prev = cvCloneImage(img);
diff = cvCreateImage(cvSize(img->width,img->height), img->depth, 1);
diff->origin = img->origin;
// start main loop
while (keepProcessing) {
int64 timeStart = getTickCount(); // get time at start of loop
// make copy of previous image frame
cvCopy(img, prev, NULL);
// if capture object in use (i.e. video/camera)
// get image from capture object
if (capture) {
// cvQueryFrame is just a combination of cvGrabFrame
// and cvRetrieveFrame in one call.
img = cvQueryFrame(capture);
if(!img){
if (argc == 2){
printf("End of video file reached\n");
} else {
printf("ERROR: cannot get next fram from camera\n");
}
exit(0);
}
} else {
// if not a capture object set event delay to zero so it waits
// indefinitely (as single image file, no need to loop)
EVENT_LOOP_DELAY = 0;
}
// do change detection using image differencing with adaptive threshold
// Reference: [P.Rosin, Thresholding for change detection, ICCV, 1998 ]
// N.B. This function requires 3-channel inputs
// (prev & current frames) and a 1-channel output (diff)
cvChangeDetection(prev, img, diff);
// display images in windows
cvShowImage( windowNameBG, img );
cvShowImage( windowNameFG, diff );
// start event processing loop (very important,in fact essential for GUI)
// 40 ms roughly equates to 1000ms/25fps = 4ms per frame
// here we take account of processing time for the loop by subtracting the time
// taken in ms. from this (1000ms/25fps = 40ms per frame) value whilst ensuring
// we get a +ve wait time
key = cvWaitKey((int) std::max(2.0, EVENT_LOOP_DELAY -
(((getTickCount() - timeStart) / getTickFrequency()) * 1000)));
if (key == 'x'){
// if user presses "x" then exit
printf("Keyboard exit requested : exiting now - bye!\n");
keepProcessing = false;
}
}
// destroy window objects
// (triggered by event loop *only* window is closed)
cvDestroyAllWindows();
// destroy image objects (if it does not originate from a capture object)
if (!capture){
cvReleaseImage( &img );
}
cvReleaseImage( &prev );
cvReleaseImage( &diff );
// all OK : main returns 0
return 0;
}
// not OK : main returns -1
return -1;
}
/******************************************************************************/