学习OpenCV2——CamShift之目标跟踪
2016-03-31 19:20
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1. CamShift思想
Camshift全称是"Continuously Adaptive Mean-SHIFT",即连续自适应的MeanShift算法,是MeanShift算法的改进。CamShift的基本思想是视频图像的所有帧作MeanShift运算,并将上一帧的结果(即Search Window的中心和大小)作为下一帧MeanShift算法的Search Window的初始值,如此迭代下去。这个过程其实和用MeanShift做跟踪一样,可以参见我的另一篇博文“Meanshift之目标跟踪”,这里把我画的流程图搬过来。
2. cvCamShift( )详解
CamShift号称连续自适应MeanShift,在算法理论上并没有什么区别,甚至在编程的流程上也没什么区别,他们的区别体现在程序内部int cvCamShift( const void* imgProb, //概率图 CvRect windowIn, //起始跟踪区域 CvTermCriteria criteria, //迭代终止条件 CvConnectedComp* _comp, //可选参数,表示连通域结构体 CvBox2D* box ) //可选参数,存储旋转矩形的坐标,包括中心,尺寸和旋转角
和MeanShift一样,返回值是迭代次数。这里比MeanShift多了一个参数box。
函数原型见 ..\OpenCV249\sources\modules\video\src\camshift.cpp
CV_IMPL int cvCamShift( const void* imgProb, CvRect windowIn, CvTermCriteria criteria, CvConnectedComp* _comp, CvBox2D* box ) { const int TOLERANCE = 10; //公差=10 CvMoments moments; double m00 = 0, m10, m01, mu20, mu11, mu02, inv_m00; double a, b, c, xc, yc; double rotate_a, rotate_c; double theta = 0, square; double cs, sn; double length = 0, width = 0; int itersUsed = 0; CvConnectedComp comp; CvMat cur_win, stub, *mat = (CvMat*)imgProb; CV_FUNCNAME( "cvCamShift" ); comp.rect = windowIn; __BEGIN__; CV_CALL( mat = cvGetMat( mat, &stub )); //调用cvMeanShift函数 CV_CALL( itersUsed = cvMeanShift( mat, windowIn, criteria, &comp )); windowIn = comp.rect; //-------------下面的程序是和MeanShift( )的区别所在------------ //区别1:对边界情况进行处理, //CamShift()中将windowIn沿x和y方向拉大了2个TOLERANCE,并且确保windowIn不越界。Meanshift无此操作 windowIn.x -= TOLERANCE; if( windowIn.x < 0 ) windowIn.x = 0; windowIn.y -= TOLERANCE; if( windowIn.y < 0 ) windowIn.y = 0; windowIn.width += 2 * TOLERANCE; if( windowIn.x + windowIn.width > mat->width ) windowIn.width = mat->width - windowIn.x; windowIn.height += 2 * TOLERANCE; if( windowIn.y + windowIn.height > mat->height ) windowIn.height = mat->height - windowIn.y; CV_CALL( cvGetSubRect( mat, &cur_win, windowIn ));//在mat中提取windowIn区域 /* Calculating moments in new center mass */ //计算新中心处的颜色统计矩 CV_CALL( cvMoments( &cur_win, &moments )); //区别2:计算并保存了目标旋转的结果,meanshit()并未考虑旋转 m00 = moments.m00; //0阶空间矩 m10 = moments.m10; //水平1阶 m01 = moments.m01; //垂直1阶 mu11 = moments.mu11; //水平垂直2阶中心距 mu20 = moments.mu20; //水平2阶 mu02 = moments.mu02; //垂直2阶 //目标矩形的质量太小了就退出 if( fabs(m00) < DBL_EPSILON )//系统预定于的值,DBL_EPSILON=2.2204460492503131e-016 EXIT; //质量的倒数,只是为了下面计算方便,可以把除法表示成乘法 inv_m00 = 1. / m00; xc = cvRound( m10 * inv_m00 + windowIn.x ); yc = cvRound( m01 * inv_m00 + windowIn.y ); //(xc,yc)是重心相对于图像的坐标想 a = mu20 * inv_m00; b = mu11 * inv_m00; c = mu02 * inv_m00; /* Calculating width & height */ square = sqrt( 4 * b * b + (a - c) * (a - c) ); /* Calculating orientation */ //计算目标主轴方向角度 theta = atan2( 2 * b, a - c + square ); //theta是与x轴的夹角 /* Calculating width & length of figure */ cs = cos( theta ); sn = sin( theta ); rotate_a = cs * cs * mu20 + 2 * cs * sn * mu11 + sn * sn * mu02; rotate_c = sn * sn * mu20 - 2 * cs * sn * mu11 + cs * cs * mu02; //下次搜索窗口的长宽,注意不是width和height length = sqrt( rotate_a * inv_m00 ) * 4; width = sqrt( rotate_c * inv_m00 ) * 4; /*根据length和width的大小对length、width、theta进行调整*/ if( length < width ) { double t; CV_SWAP( length, width, t ); CV_SWAP( cs, sn, t ); theta = CV_PI*0.5 - theta; } /* 结果保存在comp中 */ if( _comp || box ) { int t0, t1; int _xc = cvRound( xc ); int _yc = cvRound( yc ); t0 = cvRound( fabs( length * cs )); t1 = cvRound( fabs( width * sn )); t0 = MAX( t0, t1 ) + 2; comp.rect.width = MIN( t0, (mat->width - _xc) * 2 ); t0 = cvRound( fabs( length * sn )); t1 = cvRound( fabs( width * cs )); t0 = MAX( t0, t1 ) + 2; comp.rect.height = MIN( t0, (mat->height - _yc) * 2 ); comp.rect.x = MAX( 0, _xc - comp.rect.width / 2 ); comp.rect.y = MAX( 0, _yc - comp.rect.height / 2 ); comp.rect.width = MIN( mat->width - comp.rect.x, comp.rect.width ); comp.rect.height = MIN( mat->height - comp.rect.y, comp.rect.height ); comp.area = (float) m00; } __END__; if( _comp ) *_comp = comp; if( box ) //box里存的是目标的相关参数 { box->size.height = (float)length; box->size.width = (float)width; box->angle = (float)(theta*180./CV_PI); box->center = cvPoint2D32f( comp.rect.x + comp.rect.width*0.5f, comp.rect.y + comp.rect.height*0.5f); } return itersUsed; //返回迭代次数 }
将CamShift( )和MeanShift( )对比,可以看到这些差别
1、CamShift( )中将cur_win沿x和y方向拉大了2个TOLERANCE,MeanShift( )无此操作
2、CamShift( )考虑了目标发生旋转的情况,并给出了旋转角,MeanShift( )无此操作
3.实验代码及结果
来看看OpenCV自带的demo,原程序见D:\Programs_L\OpenCV249\sources\samples\cpp\camshiftdemo.cpp#include "opencv2/video/tracking.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"
#include <iostream>
#include <ctype.h>
using namespace cv;
using namespace std;
Mat image;
bool backprojMode = false;
bool selectObject = false;
int trackObject = 0;
bool showHist = true;
Point origin;
Rect selection;
int vmin = 10, vmax = 256, smin = 30;
static void onMouse( int event, int x, int y, int, void* )
{
if( selectObject )
{
selection.x = MIN(x, origin.x);
selection.y = MIN(y, origin.y);
selection.width = std::abs(x - origin.x);
selection.height = std::abs(y - origin.y);
selection &= Rect(0, 0, image.cols, image.rows);
}
switch( event )
{
case CV_EVENT_LBUTTONDOWN:
origin = Point(x,y);
selection = Rect(x,y,0,0);
selectObject = true;
break;
case CV_EVENT_LBUTTONUP:
selectObject = false;
if( selection.width > 0 && selection.height > 0 )
trackObject = -1;
break;
}
}
static void help()
{
cout << "\nThis is a demo that shows mean-shift based tracking\n"
"You select a color objects such as your face and it tracks it.\n"
"This reads from video camera (0 by default, or the camera number the user enters\n"
"Usage: \n"
" ./camshiftdemo [camera number]\n";
cout << "\n\nHot keys: \n"
"\tESC - quit the program\n"
"\tc - stop the tracking\n"
"\tb - switch to/from backprojection view\n"
"\th - show/hide object histogram\n"
"\tp - pause video\n"
"To initialize tracking, select the object with mouse\n";
}
const char* keys =
{
"{1| | 0 | camera number}"
};
int main( int argc, const char** argv )
{
help();
VideoCapture cap;
Rect trackWindow;
int hsize = 16;
float hranges[] = {0,180};
const float* phranges = hranges;
CommandLineParser parser(argc, argv, keys);
int camNum = parser.get<int>("1");
cap.open(camNum);
if( !cap.isOpened() )
{
help();
cout << "***Could not initialize capturing...***\n";
cout << "Current parameter's value: \n";
parser.printParams();
return -1;
}
namedWindow( "Histogram", 0 );
namedWindow( "CamShift Demo", 0 );
setMouseCallback( "CamShift Demo", onMouse, 0 );
createTrackbar( "Vmin", "CamShift Demo", &vmin, 256, 0 );
createTrackbar( "Vmax", "CamShift Demo", &vmax, 256, 0 );
createTrackbar( "Smin", "CamShift Demo", &smin, 256, 0 );
Mat frame, hsv, hue, mask, hist, histimg = Mat::zeros(200, 320, CV_8UC3), backproj;
bool paused = false;
for(;;)
{
if( !paused )
{
cap >> frame;
if( frame.empty() )
break;
}
frame.copyTo(image);
if( !paused )
{
cvtColor(image, hsv, COLOR_BGR2HSV);
if( trackObject )
{
int _vmin = vmin, _vmax = vmax;
inRange(hsv, Scalar(0, smin, MIN(_vmin,_vmax)),
Scalar(180, 256, MAX(_vmin, _vmax)), mask); //mask初始化
int ch[] = {0, 0};
hue.create(hsv.size(), hsv.depth());
mixChannels(&hsv, 1, &hue, 1, ch, 1); //提取h通道
if( trackObject < 0 )
{
Mat roi(hue, selection), maskroi(mask, selection);
calcHist(&roi, 1, 0, maskroi, hist, 1, &hsize, &phranges); //计算目标直方图
normalize(hist, hist, 0, 255, CV_MINMAX);
trackWindow = selection;
trackObject = 1;
histimg = Scalar::all(0);
int binW = histimg.cols / hsize;
Mat buf(1, hsize, CV_8UC3);
for( int i = 0; i < hsize; i++ )
buf.at<Vec3b>(i) = Vec3b(saturate_cast<uchar>(i*180./hsize), 255, 255);
cvtColor(buf, buf, CV_HSV2BGR);
for( int i = 0; i < hsize; i++ )
{
int val = saturate_cast<int>(hist.at<float>(i)*histimg.rows/255);
rectangle( histimg, Point(i*binW,histimg.rows),
Point((i+1)*binW,histimg.rows - val),
Scalar(buf.at<Vec3b>(i)), -1, 8 );
}
}
calcBackProject(&hue, 1, 0, hist, backproj, &phranges);
backproj &= mask;
RotatedRect trackBox = CamShift(backproj, trackWindow,
TermCriteria( CV_TERMCRIT_EPS | CV_TERMCRIT_ITER, 10, 1 ));
if( trackWindow.area() <= 1 )
{
int cols = backproj.cols, rows = backproj.rows, r = (MIN(cols, rows) + 5)/6;
trackWindow = Rect(trackWindow.x - r, trackWindow.y - r,
trackWindow.x + r, trackWindow.y + r) &
Rect(0, 0, cols, rows);
}
if( backprojMode )
cvtColor( backproj, image, COLOR_GRAY2BGR );
ellipse( image, trackBox, Scalar(0,0,255), 3, CV_AA );
//rectangle( image, trackBox, Scalar(0,0,255), 3, CV_AA );
}
}
else if( trackObject < 0 )
paused = false;
if( selectObject && selection.width > 0 && selection.height > 0 )
{
Mat roi(image, selection);
bitwise_not(roi, roi);
}
imshow( "CamShift Demo", image );
imshow( "Histogram", histimg );
char c = (char)waitKey(10);
if( c == 27 )
break;
switch(c)
{
case 'b':
backprojMode = !backprojMode;
break;
case 'c':
trackObject = 0;
histimg = Scalar::all(0);
break;
case 'h':
showHist = !showHist;
if( !showHist )
destroyWindow( "Histogram" );
else
namedWindow( "Histogram", 1 );
break;
case 'p':
paused = !paused;
break;
default:
;
}
}
return 0;
}实验效果和之前的MeanShift差不多,图就懒得帖了。
用的时候感觉有时候甚至不如MeanShift。比如用meanshift跟踪时,手消失在人脸的位置后,meanshift会跟踪人脸,当人手再次从人脸位置出现时,会再跟踪手;而camshift被人脸干扰后,不会再跟踪手。原因未明。。。
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