运动跟踪（三）：CamShift（），对象跟踪

opencv2中的函数CamShift，内部调用的是cvCamShift，cvCamShift的内部又使用了cvMeanShift。

cv::RotatedRect cv::CamShift( InputArray _probImage, Rect& window,
                              TermCriteria criteria )
{
    CvConnectedComp comp;
    CvBox2D box;

    box.center.x = box.center.y = 0; box.angle = 0; box.size.width = box.size.height = 0;
    comp.rect.x = comp.rect.y = comp.rect.width = comp.rect.height = 0;

    Mat probImage = _probImage.getMat();
    CvMat c_probImage = probImage;
    cvCamShift(&c_probImage, window, (CvTermCriteria)criteria, &comp, &box);
    window = comp.rect;
    return RotatedRect(Point2f(box.center), Size2f(box.size), box.angle);
}

int cvCamShift( const CvArr* prob_image, CvRect window, CvTermCriteria criteria,
                CvConnectedComp* comp, CvBox2D* box=NULL );
prob_image
目标直方图的反向投影 (见 cvCalcBackProject).
window
初始搜索窗口
criteria
确定窗口搜索停止的准则
comp
生成的结构，包含收敛的搜索窗口坐标 (comp->rect 字段) 与窗口内部所有象素点的和 (comp->area 字段).
box
目标的带边界盒子。如果非 NULL, 则包含目标的尺寸和方向。
函数 cvCamShift 实现了 CAMSHIFT 目标跟踪算法([Bradski98]). 首先它调用函数 cvMeanShift 寻找目标中心，然后计算目标尺寸和方向。最后返回函数 cvMeanShift 中的迭代次数。

（1）CamShift示例代码

// CamShiftDemo.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"


#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(1);

	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);
				int ch[] = {0, 0};
				hue.create(hsv.size(), hsv.depth());
				mixChannels(&hsv, 1, &hue, 1, ch, 1);

				if( trackObject < 0 )
				{
					Mat roi(hue, selection), maskroi(mask, selection);
					calcHist(&roi, 1, 0, maskroi, hist, 1, &hsize, &phranges);
					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 );
			}
		}
		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;
}

（2）测试效果