改进Zhang Suen细化算法的C#实现
本文主要实现了改进Zhang Suen细化算法的C#实现，相关论文 ：“牟少敏,杜海洋,苏平,查绪恒,陈光艺.一种改进的快速并行细化算法[J].微电子学与计算机,2013,(第1期)” 。这篇论文中关于Zhang Suen细化算法的描述，貌似存在问题。本文的算法中的意思是两次标记的点迭代后同时删除。而zhang快速算法，是分为两步删除边界点的。第一步迭代之后，已经做标记的点就需要删除了。如果两步可以放在一起删除的话，为什么不在一次迭代中将几个条件一起判断呢
一：Zhang-Suen细化算法介绍
Zhang-Suen细化算法通常是一个迭代算法，整个迭代过程分为两步：
Step One：循环所有前景像素点，对符合如下条件的像素点标记为删除：
1. 2 <= N(p1) <=6
2. S(P1) = 1
3. P2 * P4 * P6 = 0
4. P4 * P6 * P8 = 0
其中N(p1)表示跟P1相邻的8个像素点中，为前景像素点的个数
S(P1)表示从P2 ～ P9 ～ P2像素中出现0～1的累计次数，其中0表示背景，1表示前景
完整的P1 ～P9的像素位置与举例如下：
其中 N(p1) = 4, S(P1) = 3, P2*P4*P6=0*0*0=0, P4*P6*P8=0*0*1=0, 不符合条件，无需标记为删除。
Step Two：跟Step One很类似，条件1、2完全一致，只是条件3、4稍微不同，满足如下条件的像素P1则标记为删除，条件如下：
1. 2 <= N(p1) <=6
2. S(P1) = 1
3. P2 * P4 * P8 = 0
4. P2 * P6 * P8 = 0
循环上述两步骤，直到两步中都没有像素被标记为删除为止，输出的结果即为二值图像细化后的骨架。
二：代码实现步骤
#region 改进 Zhang-Suen algorithm public Bitmap zhang_thinimage_improve(Bitmap bmp) { int imgWidth = bmp.Width; int imgHeight = bmp.Height; byte[,] BinaryArray = new byte[imgHeight, imgWidth]; int depth = Bitmap.GetPixelFormatSize(bmp.PixelFormat); if (depth != 1)//判断位深度 { int threshold = 0; BinaryArray = ToBinaryArray(bmp, out threshold); } else { BinaryArray = BinaryBitmapToBinaryArray(bmp); } int[] Zhangmude = new int[9]; //int deletecount = 0; List<Point> deletelist = new List<Point>(); while (true) { for (int y = 1; y < imgHeight-1; y++) { for (int x = 1; x < imgWidth-2; x++) { if (BinaryArray[y, x] == 0) { Zhangmude[0] = 1; if (BinaryArray[y - 1, x] == 0) Zhangmude[1] = 1; else Zhangmude[1] = 0; if (BinaryArray[y - 1, x + 1] == 0) Zhangmude[2] = 1; else Zhangmude[2] = 0; if (BinaryArray[y, x + 1] == 0) Zhangmude[3] = 1; else Zhangmude[3] = 0; if (BinaryArray[y + 1, x + 1] == 0) Zhangmude[4] = 1; else Zhangmude[4] = 0; if (BinaryArray[y + 1, x] == 0) Zhangmude[5] = 1; else Zhangmude[5] = 0; if (BinaryArray[y + 1, x - 1] == 0) Zhangmude[6] = 1; else Zhangmude[6] = 0; if (BinaryArray[y, x - 1] == 0) Zhangmude[7] = 1; else Zhangmude[7] = 0; if (BinaryArray[y - 1, x - 1] == 0) Zhangmude[8] = 1; else Zhangmude[8] = 0; int whitepointtotal = 0; for (int k = 1; k < 9; k++) { //得到1的个数 whitepointtotal = whitepointtotal + Zhangmude[k]; } if ((whitepointtotal >= 2) && (whitepointtotal <= 6)) { //得到01的个数 int ap = 0; if ((Zhangmude[1] == 0) && (Zhangmude[2] == 1)) ap++; if ((Zhangmude[2] == 0) && (Zhangmude[3] == 1)) ap++; if ((Zhangmude[3] == 0) && (Zhangmude[4] == 1)) ap++; if ((Zhangmude[4] == 0) && (Zhangmude[5] == 1)) ap++; if ((Zhangmude[5] == 0) && (Zhangmude[6] == 1)) ap++; if ((Zhangmude[6] == 0) && (Zhangmude[7] == 1)) ap++; if ((Zhangmude[7] == 0) && (Zhangmude[8] == 1)) ap++; if ((Zhangmude[8] == 0) && (Zhangmude[1] == 1)) ap++; //计算bp int bp = 0; bp += Zhangmude[1]; bp += Zhangmude[2] << 1; bp += Zhangmude[3] << 2; bp += Zhangmude[4] << 3; bp += Zhangmude[5] << 4; bp += Zhangmude[6] << 5; bp += Zhangmude[7] << 6; bp += Zhangmude[8] << 7; if (ap == 1 || bp == 65 || bp == 5 || bp == 20 || bp == 80 || bp == 13 || bp == 22 || bp == 52 || bp == 133 || bp == 141 || bp == 54) { if ((Zhangmude[1] * Zhangmude[3] * Zhangmude[5] == 0) && (Zhangmude[3] * Zhangmude[5] * Zhangmude[7] == 0)) { deletelist.Add(new Point(y, x)); } } } } } } if (deletelist.Count() == 0) break; foreach (var deleteItem in deletelist) { BinaryArray[deleteItem.X, deleteItem.Y] = 255; } deletelist.Clear(); for (int y = 1; y < imgHeight-1; y++) { for (int x = 1; x < imgWidth-1; x++) { if (BinaryArray[y, x] == 0) { Zhangmude[0] = 1; if (BinaryArray[y - 1, x] == 0) Zhangmude[1] = 1; else Zhangmude[1] = 0; if (BinaryArray[y - 1, x + 1] == 0) Zhangmude[2] = 1; else Zhangmude[2] = 0; if (BinaryArray[y, x + 1] == 0) Zhangmude[3] = 1; else Zhangmude[3] = 0; if (BinaryArray[y + 1, x + 1] == 0) Zhangmude[4] = 1; else Zhangmude[4] = 0; if (BinaryArray[y + 1, x] == 0) Zhangmude[5] = 1; else Zhangmude[5] = 0; if (BinaryArray[y + 1, x - 1] == 0) Zhangmude[6] = 1; else Zhangmude[6] = 0; if (BinaryArray[y, x - 1] == 0) Zhangmude[7] = 1; else Zhangmude[7] = 0; if (BinaryArray[y - 1, x - 1] == 0) Zhangmude[8] = 1; else Zhangmude[8] = 0; int whitepointtotal = 0; for (int k = 1; k < 9; k++) { //得到1的个数 whitepointtotal = whitepointtotal + Zhangmude[k]; } if ((whitepointtotal >= 2) && (whitepointtotal <= 6)) { //得到01的个数 int ap = 0; if ((Zhangmude[1] == 0) && (Zhangmude[2] == 1)) ap++; if ((Zhangmude[2] == 0) && (Zhangmude[3] == 1)) ap++; if ((Zhangmude[3] == 0) && (Zhangmude[4] == 1)) ap++; if ((Zhangmude[4] == 0) && (Zhangmude[5] == 1)) ap++; if ((Zhangmude[5] == 0) && (Zhangmude[6] == 1)) ap++; if ((Zhangmude[6] == 0) && (Zhangmude[7] == 1)) ap++; if ((Zhangmude[7] == 0) && (Zhangmude[8] == 1)) ap++; if ((Zhangmude[8] == 0) && (Zhangmude[1] == 1)) ap++; //计算bp int bp = 0; bp += Zhangmude[1]; bp += Zhangmude[2] << 1; bp += Zhangmude[3] << 2; bp += Zhangmude[4] << 3; bp += Zhangmude[5] << 4; bp += Zhangmude[6] << 5; bp += Zhangmude[7] << 6; bp += Zhangmude[8] << 7; if (ap == 1 || bp == 65 || bp == 5 || bp == 20 || bp == 80 || bp == 13 || bp == 22 || bp == 52 || bp == 133 || bp == 141 || bp == 54) { if ((Zhangmude[1] * Zhangmude[3] * Zhangmude[7] == 0) && (Zhangmude[1] * Zhangmude[5] * Zhangmude[7] == 0)) { deletelist.Add(new Point(y, x)); } } } } } } if (deletelist.Count() == 0) break; foreach (var deleteItem in deletelist) { BinaryArray[deleteItem.X, deleteItem.Y] = 255; } deletelist.Clear(); } Bitmap dstBmp = BinaryArrayToBinaryBitmap(BinaryArray); return dstBmp; } #endregion
还有一个问题需要注意，找到要删除的点之后不能立即删除，而是把找到的点做标记，等第一步全部遍历完之后才删除标记的点。同样第二步也是这样。
下面是实验结果：
本文借鉴了两篇博客，下面是原文地址：
https://blog.csdn.net/u011941438/article/details/54628836
https://blog.csdn.net/jia20003/article/details/52142992
