由於最近做實驗用到二值影象連通區域（八連通）標記，剛開始的時候為了驗證演算法有效性，用了遞迴的方法（太慢了，而且影象一大就容易棧溢位），最後查看了opencv和MATLAB的實現，做個記錄。（為了簡單說明，以下說明已四連通為例）

掃描法連通區域標記：

例：對於二值影象、四連通

第一次遍歷：

1.建立一個和影象大小一樣的矩陣儲存結果，原圖記為im,結果矩陣記為mask,mask各元素值可初始化為0. 從上到下，從左到右掃描原影象，變數Mark記錄當前賦值

2.若當前訪問畫素座標（i,j）且im[i,j]不為0，訪問mask[i-1][j](若未越界)和mask[i,j-1]（若未越界）,二者若均為0，Mark++，賦值給當前座標對應的mask. 若其中一個為0，將非0值賦值給mask[i][j]。 若均非0且相等，將mask[i][j]標記為同一類，若不等將二者最小值賦予mask[i][j],同時將二者合併為同一類（並查集）。

第二次遍歷：

根據並查集的內容對區域賦值。

def countRegion(img):
    [high,width] = np.shape(img)
    mask  = np.zeros_like(img)
    mark  = 0
    union = {}
    for i in range (high):
        for j in range(width):
            if i==0 and j==0:
                if img[i][j]==255:
                    mark=mark+1
                    mask[i][j]=mark
                    union[mark]=mark
            if i==0 and j!=0:
                if img[i][j]==255:
                    left = mask[i][j-1]
                    if left!=0:
                        mask[i][j]=left
                    else:
                        mark = mark +1
                        mask[i][j]=mark
                        union[mark]=mark
            if  j==0 and i!=0:
                if img[i][j]==255:
                    up  = mask[i-1][j]
                    up_right = mask[i-1][j+1]
                    if up==0 and up_right==0:
                        mark = mark+1
                        mask[i][j]=mark
                        union[mark]=mark
                    if up==0 and up_right!=0:
                        mask[i][j]=up_right
                    if up_right==0 and up!=0:
                        mask[i][j]=up
                    if up!=0 and up_right!=0:
                        if up==up_right:
                            mask[i][j]=up
                        else:
                            mi = min(up,up_right)
                            mask[i][j]=mi
                            if up<up_right:
                                union[up_right]=up
                            else:
                                union[up]=up_right
            if i!=0 and j!=0:
                if img[i][j]==255:
                    up = mask[i-1][j]
                    up_left = mask[i-1][j-1]
                    left = mask[i][j-1]
                    up_right = 0
                    if j+1<width:
                        up_right = mask[i-1][j+1]
                    ma = max(max(max(up,up_left),up_right),left)
                    if ma==0:
                        mark = mark+1
                        mask[i][j]=mark
                        union[mark]=mark
                    else:
                        if up==up_right and up_right==up_left and up==left:
                            mask[i][j]=up
                        else:
                            mi = min(min(min(up, up_left), up_right), left)
                            if mi!=0:
                                mask[i][j]=mi
                                if up!=mi:
                                    union[up]=mi
                                if up_right!=mi:
                                    union[up_right]=mi
                                if up_left!=mi:
                                    union[up_left]=mi
                                if left!=mi:
                                    union[left]=mi
                            else:
                                n_zero = []
                                if up!=0:
                                    n_zero.append(up)
                                if up_left!=0:
                                    n_zero.append(up_left)
                                if up_right!=0:
                                    n_zero.append(up_right)
                                if left!=0:
                                    n_zero.append(left)
                                mi1 = min(n_zero)
                                mask[i][j]=mi1
                                for it in n_zero:
                                    if it!=mi1:
                                        union[it]=mi1
    for i in range(high):
        for j in range(width):
            key = mask[i][j]
            if key!=0:
                while union[key]!=key:
                    key = union[key]
                mask[i][j]=key
    return mask
 

八鄰域連通區域標記Python實現

參考：MATLAB，opencv連通區域標記演算法