OpenCV - 区域生长法、均值迭代、OSTU、最大熵分割方法

1、区域生长法

区域生长法是一种基于广度优先的分割方法，实现方法如下：

/**
 *@brief 区域生长法，输入图像应为灰度图
 *@para srcImg 区域生长原图像
 *@para pt 种子点
 *@para thre 阈值
**/
void RegionGrowing(Mat srcImg, Mat& dstImg, Point pt, int thre)
{
	// Mat RegionGrowing(Mat srcImg, Point pt, int thre)
	// return growImage.clone();
	Point ptGrowing; //待生长点坐标
	int nGrowLabel = 0; //是否被标记 markImage灰度值不为0
	int startPtValue = 0; //生长起始点灰度值
	int currPtValue = 0; //当前生长点灰度值
	//int growPtValue = 0; //待生长点灰度值
 
	Mat markImg = Mat::zeros(srcImg.size(), CV_8UC1);//创建一个空白区域，填充颜色为黑色
	int mDir[8][2] = { { -1,-1 },{ 0,-1 },{ 1,-1 },{ -1,0 },{ 1,0 },{ -1,1 },{ 0,1 },{ 1,1 } };   //8邻域
 
	vector growPtVec;//生长点栈
	growPtVec.push_back(pt);//将初始生长点压入栈
	
	//unsigned char *pData = (unsigned char *)(markImg.data + pt.y*markImg.step);
	//pData[pt.x] = 255;//标记初始生长点
	markImg.at(pt) = 255;
 
	//startPtValue = ((unsigned char*)(srcImg.data + pt.y*srcImg.step))[pt.x];//该像素点所在行的首地址,然后再加上该像素点所在的列
	startPtValue = srcImg.at(pt);
	
	while (!growPtVec.empty())
	{
		Point currPt = growPtVec.back(); //返回当前vector最末一个元素
		growPtVec.pop_back(); //弹出最后压入的数据
		for (int i = 0; i < 8; i++)
		{
			ptGrowing.x = currPt.x + mDir[i][0];
			ptGrowing.y = currPt.y + mDir[i][1];
			//判断是否是边缘点
			if (ptGrowing.x < 0 || ptGrowing.y < 0 || (ptGrowing.x > srcImg.cols - 1) || (ptGrowing.y > srcImg.rows - 1))
				continue;//继续执行下一次循环
					 //判断是否已被标记
			//nGrowLabel = ((unsigned char*)(markImg.data + ptGrowing.y*markImg.step))[ptGrowing.x];
			nGrowLabel = markImg.at(ptGrowing);
			if (nGrowLabel == 0) //没有被标记
			{
				//currPtValue = ((unsigned char*)(srcImg.data + ptGrowing.y*srcImg.step))[ptGrowing.x];
				//currPtValue = srcImg.at(currPt.y, currPt.x);
				currPtValue = srcImg.at(ptGrowing);
				if (abs(currPtValue - startPtValue) <= thre)
				{
					//((unsigned char*)(markImg.data + ptGrowing.y*markImg.step))[ptGrowing.x] = 255;
					markImg.at(ptGrowing) = 255;
					growPtVec.push_back(ptGrowing);
				}
			}
		}
	}
	markImg.copyTo(dstImg);
}

---

接下来是基于阈值的分割方法

2、均值迭代分割

上图是一个图像的灰度直方图，那么均值迭代的目标就是要找一个阈值，使两边的均值相等。均值迭代一般比较使用直方图为典型的“双峰”的图像

算法步骤：

1、设定一个初始化阈值T

2、计算两部分的灰度均值u1，u2.（这边很像OTSU）

3、更新T=（u1 + u2）/ 2，重复2，3

4、使用T来分割图像

void MeanIteration(Mat& img, int n) {
	int thres = 0;
	int nCol = img.cols*img.channels();

	while (abs(thres - n) > 10)
	{
		int meanO = 0;
		int nObject = 0;
		int meanB = 0;
		int nBack = 0;
		thres = n;
		for (int i = 0; i < img.rows; i++)
		{
			uchar* pData = img.ptr(i);
			for (int j = 0; j < nCol; j++)
			{
				if (pData[j] < thres)
				{
					++nBack;
					meanB += pData[j];
				}
				else
				{
					++nObject;
					meanO += pData[j];
				}
			}
		}

		if (nBack == 0 || nObject == 0)
			continue;
		n = (meanB / nBack + meanO / nObject) / 2;
	}
	threshold(img, img, n, 255, 0);
}

---

3、OTSU分割算法 - 最大类间方差

https://blog.csdn.net/qq_41828351/article/details/88718246

---

4、最大熵分割

最大熵分割：公式参考https://blog.csdn.net/Robin__Chou/article/details/53931442

和上面集中方法做比较来看，其实就是用不同的方法来计算阈值的。（代码和OTSU的实现方式相同）

Mat entropySeg(Mat& src)
{
	int tbHist[256] = { 0 };                                        //每个像素值个数
	int index = 0;                                                  //最大熵对应的灰度
	double Property = 0.0;                                          //像素所占概率
	double maxEntropy = -1.0;                                       //最大熵
	double frontEntropy = 0.0;                                      //前景熵
	double backEntropy = 0.0;                                       //背景熵
	//纳入计算的总像素数
	int TotalPixel = 0;
	int nCol = src.cols * src.channels();                           //每行的像素个数
	for (int i = 0; i < src.rows; i++)
	{
		uchar* pData = src.ptr(i);
		for (int j = 0; j < nCol; ++j)
		{
			++TotalPixel;
			tbHist[pData[j]] += 1;
		}
	}

	for (int i = 0; i < 256; i++)
	{
		//计算背景像素数
		double backTotal = 0;
		for (int j = 0; j < i; j++)
		{
			backTotal += tbHist[j];
		}

		//背景熵
		for (int j = 0; j < i; j++)
		{
			if (tbHist[j] != 0)
			{
				Property = tbHist[j] / backTotal;
				backEntropy += -Property * logf((float)Property);
			}
		}
		//前景熵
		for (int k = i; k < 256; k++)
		{
			if (tbHist[k] != 0)
			{
				Property = tbHist[k] / (TotalPixel - backTotal);
				frontEntropy += -Property * logf((float)Property);
			}
		}

		if (frontEntropy + backEntropy > maxEntropy)    //得到最大熵
		{
			maxEntropy = frontEntropy + backEntropy;
			index = i;
		}
		//清空本次计算熵值
		frontEntropy = 0.0;
		backEntropy = 0.0;
	}
	Mat dst;
	//index += 20;
	cv::threshold(src, dst, index, 255, 0);             //进行阈值分割
	return dst.clone();
}