opencv运用帧差法对运动物体检测

运用帧差法对运动物体检测：

定义一个阈值，下面还会建立一个灰度直方图：

	int detectThreshold = 19;

当环境变化时，直方图会产生变化，而这个阈值就是对变化的敏感性

当阈值小时，变化一点就能检测出来，阈值大了，变化一点是检测不出运动物体的

定义获取的图片大小：

	cvSetCaptureProperty(pCapture, CV_CAP_PROP_FRAME_WIDTH, 640);
	cvSetCaptureProperty(pCapture, CV_CAP_PROP_FRAME_HEIGHT, 480);

可以自己尝试改一下数值看看效果

定义亮度以及对比度：

	cvSetCaptureProperty(pCapture, CV_CAP_PROP_BRIGHTNESS, 70);
	cvSetCaptureProperty(pCapture, CV_CAP_PROP_CONTRAST, 50);

后面的数值需要自己调至合适

下面是代码

#include "cv.h"
#include "highgui.h"

int main(int argc, char** argv) {
	
	int detectThreshold = 19;

	/*初始化相机 */
	CvCapture* pCapture = cvCreateCameraCapture(1);
	cvSetCaptureProperty(pCapture, CV_CAP_PROP_FRAME_WIDTH, 640);
	cvSetCaptureProperty(pCapture, CV_CAP_PROP_FRAME_HEIGHT, 480);
	cvSetCaptureProperty(pCapture, CV_CAP_PROP_BRIGHTNESS, 70);
	cvSetCaptureProperty(pCapture, CV_CAP_PROP_CONTRAST, 50);
	if (NULL == pCapture) {
		fprintf(stderr, "Can't initialize webcam!\n");
		return 1;
	}
	

	IplImage *pFrameA = cvQueryFrame(pCapture);
	IplImage *pFrameB = cvCreateImage(cvSize(pFrameA->width, pFrameA->height), pFrameA->depth, pFrameA->nChannels);
	IplImage *pFrameDiff = cvCloneImage(pFrameB);

	int nDims = 256;
	float hRangesArr[] = { 0, 255 };
	float* hRanges = hRangesArr;

	IplImage *pGrayscaleImage = NULL;
	CvHistogram *pHist = cvCreateHist(1, &nDims, CV_HIST_ARRAY, &hRanges, 1);
	float fMaxValue = 0.0;

	time_t ts = 0;  // used to record current timestamp & prevent triggering the monition detection for multi times in 1 second
	while (true) {
		pFrameA = cvQueryFrame(pCapture);
		if (!pFrameA) {
			fprintf(stdout, "Can't grab images!\n");

			break;
		}

		cvAbsDiff(pFrameB, pFrameA, pFrameDiff);  //找出两张图片的不同s
		cvCopy(pFrameA, pFrameB);                // 复制图片

		pGrayscaleImage = cvCreateImage(cvGetSize(pFrameDiff), IPL_DEPTH_8U, 1);
		cvCvtColor(pFrameDiff, pGrayscaleImage, CV_BGR2GRAY);
		cvCalcHist(&pGrayscaleImage, pHist, 0, 0);

		fMaxValue = 0.0;
		cvGetMinMaxHistValue(pHist, 0, &fMaxValue, 0, 0);
		cvConvertScale(pHist->bins, pHist->bins, (fMaxValue ? (255.0 / fMaxValue) : 0.0), 0);

		double dRealtimeVal = cvGetReal1D(pHist->bins, 10);
		if (dRealtimeVal > detectThreshold) {  // triggered
			time_t currentTimestamp = time(NULL);
			if (currentTimestamp - ts >= 1) {
				ts = currentTimestamp;
				printf("Motion detected @ %s", ctime(¤tTimestamp));
			}
		}

		cvReleaseImage(&pGrayscaleImage);  // 释放缓存

		pGrayscaleImage = NULL;

		cvWaitKey(10);  // 等待10ms
	}

	cvReleaseCapture(&pCapture);  // 释放资源
	cvReleaseHist(&pHist);
	cvReleaseImage(&pFrameA);
	cvReleaseImage(&pFrameB);
	cvReleaseImage(&pFrameDiff);

	pCapture = NULL;
	pHist = NULL;
	pFrameA = NULL;
	pFrameB = NULL;
	pFrameDiff = NULL;

	return 0;
}

效果图：