【OpenCV】图像代数运算:平均值去噪,减去背景
2016-05-07 09:38
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代数运算,就是对两幅图像的点之间进行加、减、乘、除的运算。四种运算相应的公式为:
![](http://my.csdn.net/uploads/201205/28/1338211280_5824.png)
代数运算中比较常用的是图像相加和相减。图像相加常用来求平均值去除addtive噪声或者实现二次曝光(double-exposure)。图像相减用于减去背景或周期噪声,污染等。
OpenCV中提供了相加的函数
[cpp] view
plain copy
void cvAcc(
const CvArr* image,//输入图像
CvArr* sum, //累积图像
const CvArr* mask=NULL//可选的运算
);
我们还需要用到一个线性变换转换函数来对相加的结果求平均
[cpp] view
plain copy
void cvConvertScale(
const CvArr* src, //输入数组
CvArr* dst,//输出数组
double scale=1,//比例
double shift=0 //缩放比例,可选
);
#define cvCvtScale cvConvertScale
#define cvScale cvConvertScale
#define cvConvert( src, dst ) cvConvertScale( (src), (dst), 1, 0 )
[cpp] view
plain copy
int main()
{
CvCapture* capture=cvCaptureFromFile("media.avi");
IplImage* frame= NULL;
IplImage * imgsum =NULL;
int start=301;
int end=304;
cvSetCaptureProperty(capture, CV_CAP_PROP_POS_FRAMES, start);
int count = start;
while( cvGrabFrame(capture) && count <= end )
{
frame = cvRetrieveFrame(capture);// 获取当前帧
if(imgsum==NULL){
imgsum=cvCreateImage(cvGetSize(frame),IPL_DEPTH_32F,3);
cvZero(imgsum);
}
cvAcc(frame,imgsum);
char testname[100];
sprintf(testname,"%s%d%s","image",count,".jpg");
cvShowImage(testname,frame);
cvSaveImage(testname,frame);
count++;
}
IplImage * imgavg = cvCreateImage(cvGetSize(frame),IPL_DEPTH_8U,3);
cvConvertScale(imgsum,imgavg,1.0/4.0);
cvShowImage("imageavg",imgavg);
cvSaveImage("imageavg_4.jpg",imgavg);
cvWaitKey(0);
cvReleaseCapture(&capture);
return 0;
}
以下从左到右分别是连续两帧、四帧、八帧、十六帧求均值的结果:
![](http://my.csdn.net/uploads/201205/28/1338213182_6643.jpg)
![](http://my.csdn.net/uploads/201205/28/1338213243_4276.jpg)
![](http://my.csdn.net/uploads/201205/28/1338213292_2609.jpg)
![](http://my.csdn.net/uploads/201205/28/1338213306_6217.jpg)
[cpp] view
plain copy
//通过求平均二次曝光
int main()
{
IplImage* image1= cvLoadImage("psu3.jpg");
IplImage* image2= cvLoadImage("psu4.jpg");
IplImage * imgsum =cvCreateImage(cvGetSize(image1),IPL_DEPTH_32F,3);
cvZero(imgsum);
cvAcc(image1,imgsum);
cvAcc(image2,imgsum);
IplImage * imgavg = cvCreateImage(cvGetSize(image1),IPL_DEPTH_8U,3);
cvConvertScale(imgsum,imgavg,1.0/2.0);
cvShowImage("imageavg",imgavg);
cvSaveImage("avg.jpg",imgavg);
cvWaitKey(0);
cvReleaseImage(&image1);
cvReleaseImage(&image2);
cvReleaseImage(&imgsum);
cvReleaseImage(&imgavg);
return 0;
}
下图是对同学街舞截图的“二次曝光”效果:
![](http://my.csdn.net/uploads/201205/28/1338213468_9223.jpg)
[cpp] view
plain copy
void cvAbsDiff(
const CvArr* src1,//第一个输入数组
const CvArr* src2,//第二个输入数组
CvArr* dst//输出数组
);
[cpp] view
plain copy
//减去背景
int main()
{
IplImage* pFrame = NULL;
IplImage* pFrImg = NULL;
IplImage* pBkImg = NULL;
CvMat* pFrameMat = NULL;
CvMat* pFrMat = NULL;
CvMat* pBkMat = NULL;
CvCapture* pCapture = NULL;
int nFrmNum = 0;
//创建窗口
cvNamedWindow("video", 1);
cvNamedWindow("background",1);
cvNamedWindow("foreground",1);
pCapture = cvCaptureFromFile("media.avi");
while(pFrame = cvQueryFrame( pCapture ))
{
nFrmNum++;
//如果是第一帧,需要申请内存,并初始化
if(nFrmNum == 1)
{
pBkImg = cvCreateImage(cvSize(pFrame->width, pFrame->height), IPL_DEPTH_8U,1);
pFrImg = cvCreateImage(cvSize(pFrame->width, pFrame->height), IPL_DEPTH_8U,1);
pBkMat = cvCreateMat(pFrame->height, pFrame->width, CV_32FC1);
pFrMat = cvCreateMat(pFrame->height, pFrame->width, CV_32FC1);
pFrameMat = cvCreateMat(pFrame->height, pFrame->width, CV_32FC1);
//转化成单通道图像再处理
cvCvtColor(pFrame, pBkImg, CV_BGR2GRAY);
cvCvtColor(pFrame, pFrImg, CV_BGR2GRAY);
cvConvert(pFrImg, pFrameMat);
cvConvert(pFrImg, pFrMat);
cvConvert(pFrImg, pBkMat);
}
else
{
cvCvtColor(pFrame, pFrImg, CV_BGR2GRAY);
cvConvert(pFrImg, pFrameMat);
//当前帧跟背景图相减
cvAbsDiff(pFrameMat, pBkMat, pFrMat);
//二值化前景图
cvThreshold(pFrMat, pFrImg, 60, 255.0, CV_THRESH_BINARY);
//更新背景
cvRunningAvg(pFrameMat, pBkMat, 0.003, 0);
//将背景转化为图像格式,用以显示
cvConvert(pBkMat, pBkImg);
cvShowImage("video", pFrame);
cvShowImage("background", pBkImg);
cvShowImage("foreground", pFrImg);
if( cvWaitKey(2) >= 0 )
break;
}
}
cvDestroyWindow("video");
cvDestroyWindow("background");
cvDestroyWindow("foreground");
cvReleaseImage(&pFrImg);
cvReleaseImage(&pBkImg);
cvReleaseMat(&pFrameMat);
cvReleaseMat(&pFrMat);
cvReleaseMat(&pBkMat);
cvReleaseCapture(&pCapture);
return 0;
}
效果图:
![](http://my.csdn.net/uploads/201205/28/1338213647_5211.png)
转载请注明出处:http://blog.csdn.net/xiaowei_cqu/article/details/7610665
![](http://my.csdn.net/uploads/201205/28/1338211280_5824.png)
代数运算中比较常用的是图像相加和相减。图像相加常用来求平均值去除addtive噪声或者实现二次曝光(double-exposure)。图像相减用于减去背景或周期噪声,污染等。
图像相加
OpenCV中提供了相加的函数[cpp] view
plain copy
void cvAcc(
const CvArr* image,//输入图像
CvArr* sum, //累积图像
const CvArr* mask=NULL//可选的运算
);
我们还需要用到一个线性变换转换函数来对相加的结果求平均
[cpp] view
plain copy
void cvConvertScale(
const CvArr* src, //输入数组
CvArr* dst,//输出数组
double scale=1,//比例
double shift=0 //缩放比例,可选
);
#define cvCvtScale cvConvertScale
#define cvScale cvConvertScale
#define cvConvert( src, dst ) cvConvertScale( (src), (dst), 1, 0 )
实践:平均值去噪
我们用NASA的一段幸运团的视频做实验,截取视频的某几个连续帧求平均值:[cpp] view
plain copy
int main()
{
CvCapture* capture=cvCaptureFromFile("media.avi");
IplImage* frame= NULL;
IplImage * imgsum =NULL;
int start=301;
int end=304;
cvSetCaptureProperty(capture, CV_CAP_PROP_POS_FRAMES, start);
int count = start;
while( cvGrabFrame(capture) && count <= end )
{
frame = cvRetrieveFrame(capture);// 获取当前帧
if(imgsum==NULL){
imgsum=cvCreateImage(cvGetSize(frame),IPL_DEPTH_32F,3);
cvZero(imgsum);
}
cvAcc(frame,imgsum);
char testname[100];
sprintf(testname,"%s%d%s","image",count,".jpg");
cvShowImage(testname,frame);
cvSaveImage(testname,frame);
count++;
}
IplImage * imgavg = cvCreateImage(cvGetSize(frame),IPL_DEPTH_8U,3);
cvConvertScale(imgsum,imgavg,1.0/4.0);
cvShowImage("imageavg",imgavg);
cvSaveImage("imageavg_4.jpg",imgavg);
cvWaitKey(0);
cvReleaseCapture(&capture);
return 0;
}
以下从左到右分别是连续两帧、四帧、八帧、十六帧求均值的结果:
![](http://my.csdn.net/uploads/201205/28/1338213182_6643.jpg)
![](http://my.csdn.net/uploads/201205/28/1338213243_4276.jpg)
![](http://my.csdn.net/uploads/201205/28/1338213292_2609.jpg)
![](http://my.csdn.net/uploads/201205/28/1338213306_6217.jpg)
实践:图像二次曝光
曝光和去噪是一样的,也是对几幅图像求平均[cpp] view
plain copy
//通过求平均二次曝光
int main()
{
IplImage* image1= cvLoadImage("psu3.jpg");
IplImage* image2= cvLoadImage("psu4.jpg");
IplImage * imgsum =cvCreateImage(cvGetSize(image1),IPL_DEPTH_32F,3);
cvZero(imgsum);
cvAcc(image1,imgsum);
cvAcc(image2,imgsum);
IplImage * imgavg = cvCreateImage(cvGetSize(image1),IPL_DEPTH_8U,3);
cvConvertScale(imgsum,imgavg,1.0/2.0);
cvShowImage("imageavg",imgavg);
cvSaveImage("avg.jpg",imgavg);
cvWaitKey(0);
cvReleaseImage(&image1);
cvReleaseImage(&image2);
cvReleaseImage(&imgsum);
cvReleaseImage(&imgavg);
return 0;
}
下图是对同学街舞截图的“二次曝光”效果:
![](http://my.csdn.net/uploads/201205/28/1338213468_9223.jpg)
图像相减
OpenCV中用cvAbsDiff函数计算两数组的差的绝对值[cpp] view
plain copy
void cvAbsDiff(
const CvArr* src1,//第一个输入数组
const CvArr* src2,//第二个输入数组
CvArr* dst//输出数组
);
实践:减去背景
减去背景是通过两幅图像代数相减,可以判断出前景区域和运动区域,这是最简单(很多时候也是效果很好的)运动检测方法。[cpp] view
plain copy
//减去背景
int main()
{
IplImage* pFrame = NULL;
IplImage* pFrImg = NULL;
IplImage* pBkImg = NULL;
CvMat* pFrameMat = NULL;
CvMat* pFrMat = NULL;
CvMat* pBkMat = NULL;
CvCapture* pCapture = NULL;
int nFrmNum = 0;
//创建窗口
cvNamedWindow("video", 1);
cvNamedWindow("background",1);
cvNamedWindow("foreground",1);
pCapture = cvCaptureFromFile("media.avi");
while(pFrame = cvQueryFrame( pCapture ))
{
nFrmNum++;
//如果是第一帧,需要申请内存,并初始化
if(nFrmNum == 1)
{
pBkImg = cvCreateImage(cvSize(pFrame->width, pFrame->height), IPL_DEPTH_8U,1);
pFrImg = cvCreateImage(cvSize(pFrame->width, pFrame->height), IPL_DEPTH_8U,1);
pBkMat = cvCreateMat(pFrame->height, pFrame->width, CV_32FC1);
pFrMat = cvCreateMat(pFrame->height, pFrame->width, CV_32FC1);
pFrameMat = cvCreateMat(pFrame->height, pFrame->width, CV_32FC1);
//转化成单通道图像再处理
cvCvtColor(pFrame, pBkImg, CV_BGR2GRAY);
cvCvtColor(pFrame, pFrImg, CV_BGR2GRAY);
cvConvert(pFrImg, pFrameMat);
cvConvert(pFrImg, pFrMat);
cvConvert(pFrImg, pBkMat);
}
else
{
cvCvtColor(pFrame, pFrImg, CV_BGR2GRAY);
cvConvert(pFrImg, pFrameMat);
//当前帧跟背景图相减
cvAbsDiff(pFrameMat, pBkMat, pFrMat);
//二值化前景图
cvThreshold(pFrMat, pFrImg, 60, 255.0, CV_THRESH_BINARY);
//更新背景
cvRunningAvg(pFrameMat, pBkMat, 0.003, 0);
//将背景转化为图像格式,用以显示
cvConvert(pBkMat, pBkImg);
cvShowImage("video", pFrame);
cvShowImage("background", pBkImg);
cvShowImage("foreground", pFrImg);
if( cvWaitKey(2) >= 0 )
break;
}
}
cvDestroyWindow("video");
cvDestroyWindow("background");
cvDestroyWindow("foreground");
cvReleaseImage(&pFrImg);
cvReleaseImage(&pBkImg);
cvReleaseMat(&pFrameMat);
cvReleaseMat(&pFrMat);
cvReleaseMat(&pBkMat);
cvReleaseCapture(&pCapture);
return 0;
}
效果图:
![](http://my.csdn.net/uploads/201205/28/1338213647_5211.png)
转载请注明出处:http://blog.csdn.net/xiaowei_cqu/article/details/7610665
实验代码及视频下载:http://download.csdn.net/detail/xiaowei_cqu/4335573
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