GrabCut--Opencv篇

最近因为工作需要，需要实现一个Grabcut函数。Opencv已经提供此函数，今天把opencv的例程拿出来跑了一下，对于简单的背景实现效果还不错。

OpenCV中的GrabCut算法是依据《"GrabCut" - Interactive Foreground Extraction using Iterated Graph Cuts》这篇文章来实现的。

此论文地址为：http://research.microsoft.com/en-us/um/people/ablake/papers/ablake/siggraph04.pdf

下面是Opencv中GrabCut函数调用事例。

#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"

#include <iostream>

using namespace std;
using namespace cv;

static void help()
{
	cout << "\nThis program demonstrates GrabCut segmentation -- select an object in a region\n"
		"and then grabcut will attempt to segment it out.\n"
		"Call:\n"
		"./grabcut <image_name>\n"
		"\nSelect a rectangular area around the object you want to segment\n" <<
		"\nHot keys: \n"
		"\tESC - quit the program\n"
		"\tr - restore the original image\n"
		"\tn - next iteration\n"
		"\n"
		"\tleft mouse button - set rectangle\n"
		"\n"
		"\tCTRL+left mouse button - set GC_BGD pixels\n"
		"\tSHIFT+left mouse button - set CG_FGD pixels\n"
		"\n"
		"\tCTRL+right mouse button - set GC_PR_BGD pixels\n"
		"\tSHIFT+right mouse button - set CG_PR_FGD pixels\n" << endl;
}

const Scalar RED = Scalar(0,0,255);
const Scalar PINK = Scalar(230,130,255);
const Scalar BLUE = Scalar(255,0,0);
const Scalar LIGHTBLUE = Scalar(255,255,160);
const Scalar GREEN = Scalar(0,255,0);

const int BGD_KEY = CV_EVENT_FLAG_CTRLKEY;  //Ctrl键
const int FGD_KEY = CV_EVENT_FLAG_SHIFTKEY; //Shift键

static void getBinMask( const Mat& comMask, Mat& binMask )
{
	if( comMask.empty() || comMask.type()!=CV_8UC1 )
		CV_Error( CV_StsBadArg, "comMask is empty or has incorrect type (not CV_8UC1)" );
	if( binMask.empty() || binMask.rows!=comMask.rows || binMask.cols!=comMask.cols )
		binMask.create( comMask.size(), CV_8UC1 );
	binMask = comMask & 1;  //得到mask的最低位,实际上是只保留确定的或者有可能的前景点当做mask
}

class GCApplication
{
public:
	enum{ NOT_SET = 0, IN_PROCESS = 1, SET = 2 };
	static const int radius = 2;
	static const int thickness = -1;

	void reset();
	void setImageAndWinName( const Mat& _image, const string& _winName );
	void showImage() const;
	void mouseClick( int event, int x, int y, int flags, void* param );
	int nextIter();
	int getIterCount() const { return iterCount; }
private:
	void setRectInMask();
	void setLblsInMask( int flags, Point p, bool isPr );

	const string* winName;
	const Mat* image;
	Mat mask;
	Mat bgdModel, fgdModel;

	uchar rectState, lblsState, prLblsState;
	bool isInitialized;

	Rect rect;
	vector<Point> fgdPxls, bgdPxls, prFgdPxls, prBgdPxls;
	int iterCount;
};

/*给类的变量赋值*/
void GCApplication::reset()
{
	if( !mask.empty() )
		mask.setTo(Scalar::all(GC_BGD));
	bgdPxls.clear(); fgdPxls.clear();
	prBgdPxls.clear();  prFgdPxls.clear();

	isInitialized = false;
	rectState = NOT_SET;    //NOT_SET == 0
	lblsState = NOT_SET;
	prLblsState = NOT_SET;
	iterCount = 0;
}

/*给类的成员变量赋值而已*/
void GCApplication::setImageAndWinName( const Mat& _image, const string& _winName  )
{
	if( _image.empty() || _winName.empty() )
		return;
	image = &_image;
	winName = &_winName;
	mask.create( image->size(), CV_8UC1);
	reset();
}

/*显示4个点，一个矩形和图像内容，因为后面的步骤很多地方都要用到这个函数，所以单独拿出来*/
void GCApplication::showImage() const
{
	if( image->empty() || winName->empty() )
		return;

	Mat res;
	Mat binMask;
	if( !isInitialized )
		image->copyTo( res );
	else
	{
		getBinMask( mask, binMask );
		image->copyTo( res, binMask );  //按照最低位是0还是1来复制，只保留跟前景有关的图像，比如说可能的前景，可能的背景
	}

	vector<Point>::const_iterator it;
	/*下面4句代码是将选中的4个点用不同的颜色显示出来*/
	for( it = bgdPxls.begin(); it != bgdPxls.end(); ++it )  //迭代器可以看成是一个指针
		circle( res, *it, radius, BLUE, thickness );
	for( it = fgdPxls.begin(); it != fgdPxls.end(); ++it )  //确定的前景用红色表示
		circle( res, *it, radius, RED, thickness );
	for( it = prBgdPxls.begin(); it != prBgdPxls.end(); ++it )
		circle( res, *it, radius, LIGHTBLUE, thickness );
	for( it = prFgdPxls.begin(); it != prFgdPxls.end(); ++it )
		circle( res, *it, radius, PINK, thickness );

	/*画矩形*/
	if( rectState == IN_PROCESS || rectState == SET )
		rectangle( res, Point( rect.x, rect.y ), Point(rect.x + rect.width, rect.y + rect.height ), GREEN, 2);

	IplImage pImg= IplImage(res); 
	IplImage *img=&pImg;
	cvShowImage(winName->c_str(),img);
	//imshow( *winName, res );
	//waitKey(30); 

}

/*该步骤完成后，mask图像中rect内部是3，外面全是0*/
void GCApplication::setRectInMask()
{
	assert( !mask.empty() );
	mask.setTo( GC_BGD );   //GC_BGD == 0
	rect.x = max(0, rect.x);
	rect.y = max(0, rect.y);
	rect.width = min(rect.width, image->cols-rect.x);
	rect.height = min(rect.height, image->rows-rect.y);
	(mask(rect)).setTo( Scalar(GC_PR_FGD) );    //GC_PR_FGD == 3，矩形内部,为可能的前景点
}

void GCApplication::setLblsInMask( int flags, Point p, bool isPr )
{
	vector<Point> *bpxls, *fpxls;
	uchar bvalue, fvalue;
	if( !isPr ) //确定的点
	{
		bpxls = &bgdPxls;
		fpxls = &fgdPxls;
		bvalue = GC_BGD;    //0
		fvalue = GC_FGD;    //1
	}
	else    //概率点
	{
		bpxls = &prBgdPxls;
		fpxls = &prFgdPxls;
		bvalue = GC_PR_BGD; //2
		fvalue = GC_PR_FGD; //3
	}
	if( flags & BGD_KEY )
	{
		bpxls->push_back(p);
		circle( mask, p, radius, bvalue, thickness );   //该点处为2
	}
	if( flags & FGD_KEY )
	{
		fpxls->push_back(p);
		circle( mask, p, radius, fvalue, thickness );   //该点处为3
	}
}

/*鼠标响应函数，参数flags为CV_EVENT_FLAG的组合*/
void GCApplication::mouseClick( int event, int x, int y, int flags, void* )
{
	// TODO add bad args check
	switch( event )
	{
	case CV_EVENT_LBUTTONDOWN: // set rect or GC_BGD(GC_FGD) labels
		{
			bool isb = (flags & BGD_KEY) != 0,
				isf = (flags & FGD_KEY) != 0;
			if( rectState == NOT_SET && !isb && !isf )//只有左键按下时
			{
				rectState = IN_PROCESS; //表示正在画矩形
				rect = Rect( x, y, 1, 1 );
			}
			if ( (isb || isf) && rectState == SET ) //按下了alt键或者shift键，且画好了矩形，表示正在画前景背景点
				lblsState = IN_PROCESS;
		}
		break;
	case CV_EVENT_RBUTTONDOWN: // set GC_PR_BGD(GC_PR_FGD) labels
		{
			bool isb = (flags & BGD_KEY) != 0,
				isf = (flags & FGD_KEY) != 0;
			if ( (isb || isf) && rectState == SET ) //正在画可能的前景背景点
				prLblsState = IN_PROCESS;
		}
		break;
	case CV_EVENT_LBUTTONUP:
		if( rectState == IN_PROCESS )
		{
			rect = Rect( Point(rect.x, rect.y), Point(x,y) );   //矩形结束
			rectState = SET;
			setRectInMask();
			assert( bgdPxls.empty() && fgdPxls.empty() && prBgdPxls.empty() && prFgdPxls.empty() );
			showImage();
		}
		if( lblsState == IN_PROCESS )   //已画了前后景点
		{
			setLblsInMask(flags, Point(x,y), false);    //画出前景点
			lblsState = SET;
			showImage();
		}
		break;
	case CV_EVENT_RBUTTONUP:
		if( prLblsState == IN_PROCESS )
		{
			setLblsInMask(flags, Point(x,y), true); //画出背景点
			prLblsState = SET;
			showImage();
		}
		break;
	case CV_EVENT_MOUSEMOVE:
		if( rectState == IN_PROCESS )
		{
			rect = Rect( Point(rect.x, rect.y), Point(x,y) );
			assert( bgdPxls.empty() && fgdPxls.empty() && prBgdPxls.empty() && prFgdPxls.empty() );
			showImage();    //不断的显示图片
		}
		else if( lblsState == IN_PROCESS )
		{
			setLblsInMask(flags, Point(x,y), false);
			showImage();
		}
		else if( prLblsState == IN_PROCESS )
		{
			setLblsInMask(flags, Point(x,y), true);
			showImage();
		}
		break;
	}
}

/*该函数进行grabcut算法，并且返回算法运行迭代的次数*/
int GCApplication::nextIter()
{
	if( isInitialized )
		//使用grab算法进行一次迭代，参数2为mask，里面存的mask位是：矩形内部除掉那些可能是背景或者已经确定是背景后的所有的点，且mask同时也为输出
		//保存的是分割后的前景图像
		grabCut( *image, mask, rect, bgdModel, fgdModel, 1 );
	else
	{
		if( rectState != SET )
			return iterCount;

		if( lblsState == SET || prLblsState == SET )
			grabCut( *image, mask, rect, bgdModel, fgdModel, 1, GC_INIT_WITH_MASK );
		else
			grabCut( *image, mask, rect, bgdModel, fgdModel, 1, GC_INIT_WITH_RECT );

		isInitialized = true;
	}
	iterCount++;

	bgdPxls.clear(); fgdPxls.clear();
	prBgdPxls.clear(); prFgdPxls.clear();

	return iterCount;
}

GCApplication gcapp;

static void on_mouse( int event, int x, int y, int flags, void* param )
{
	gcapp.mouseClick( event, x, y, flags, param );
}

int main( int argc, char** argv )
{

	char filename[]="test.jpg";
	IplImage* pImg = cvLoadImage(filename);
	
	Mat image(pImg,0); 
	if( image.empty() )
	{
		cout << "\n Durn, couldn't read image filename " << filename << endl;
		return 1;
	}
	
	help();

	const string winName = "image";
	cvNamedWindow( winName.c_str(), CV_WINDOW_AUTOSIZE );
	cvSetMouseCallback( winName.c_str(), on_mouse, 0 );

	gcapp.setImageAndWinName( image, winName );
	gcapp.showImage();

	for(;;)
	{
		int c = cvWaitKey(0);
		switch( (char) c )
		{
		case '\x1b':
			cout << "Exiting ..." << endl;
			goto exit_main;
		case 'r':
			cout << endl;
			gcapp.reset();
			gcapp.showImage();
			break;
		case 'n':
			int iterCount = gcapp.getIterCount();
			cout << "<" << iterCount << "... ";
			int newIterCount = gcapp.nextIter();
			if( newIterCount > iterCount )
			{
				gcapp.showImage();
				cout << iterCount << ">" << endl;
			}
			else
				cout << "rect must be determined>" << endl;
			break;
		}
	}

exit_main:
	cvDestroyWindow( winName.c_str() );
	return 0;
}

　　效果图大概如下：

 上三个图依次为原图、标记图片、分割后的照片，还可以继续迭代的分割，除了速度慢点，实现的效果还是非常好的。