http://blog.csdn.net/songzitea/article/details/26105609
连通区标记是最基本的图像处理算法之一。该算法中,按从左至右、从上至下的顺序,对整幅图像进行扫描,通过比较每个前景像素的邻域进行连通区标记,并创建等效标记列表。最后,合并等效标记列表,并再次扫描图像以更新标记。算法的优点的是通俗易懂,缺点是需要两次扫描图像,效率不高。
区域生长法利用区域生长的思想,一次生长过程可以标记一整个连通区,只需对图像进行一次扫描就能标记出所有连通区。算法描述如下:
- 输入待标记图像bitmap,初始化一个与输入图像同样尺寸的标记矩阵labelmap,一个队列queue以及标记计数labelIndex;
- 按从左至右、从上至下的顺序扫描bitmap,当扫描到一个未被标记的前景像素p时,labelIndex加1,并在labelmap中标记p(相应点的值赋为labelIndex),同时,扫描p的八邻域点,若存在未被标记的前景像素,则在labelmap中进行标记,并放入queue中,作为区域生长的种子;
- 当queue不为空时,从queue中取出一个生长种子点p1,扫描p1的八邻域点,若存在未被标记过的前景像素,则在labelmap中进行标记,并放入queue中;
- 重复3直至queue为空,一个连通区标记完成;
- 转到2,直至整幅图像被扫描完毕,得到标记矩阵labelmap和连通区的个数labelIndex。
该算法最坏情况下,将对每个像素点都进行一次八邻域搜索,算法复杂度为O(n)。
- typedef struct QNode{
- int data;
- struct QNode *next;
- }QNode;
- typedef struct Queue{
- struct QNode* first;
- struct QNode* last;
- }Queue;
- void PushQueue(Queue *queue, int data){
- QNode *p = NULL;
- p = (QNode*)malloc(sizeof(QNode));
- p->data = data;
- if(queue->first == NULL){
- queue->first = p;
- queue->last = p;
- p->next = NULL;
- }
- else{
- p->next = NULL;
- queue->last->next = p;
- queue->last = p;
- }
- }
- int PopQueue(Queue *queue){
- QNode *p = NULL;
- int data;
- if(queue->first == NULL){
- return -1;
- }
- p = queue->first;
- data = p->data;
- if(queue->first->next == NULL){
- queue->first = NULL;
- queue->last = NULL;
- }
- else{
- queue->first = p->next;
- }
- free(p);
- return data;
- }
- static int NeighborDirection[8][2] = {{0,1},{1,1},{1,0},{1,-1},{0,-1},{-1,-1},{-1,0},{-1,1}};
- void SearchNeighbor(unsigned char *bitmap, int width, int height, int *labelmap,
- int labelIndex, int pixelIndex, Queue *queue){
- int searchIndex, i, length;
- labelmap[pixelIndex] = labelIndex;
- length = width * height;
- for(i = 0;i < 8;i++){
- searchIndex = pixelIndex + NeighborDirection[i][0] * width + NeighborDirection[i][1];
- if(searchIndex > 0 && searchIndex < length &&
- bitmap[searchIndex] == 255 && labelmap[searchIndex] == 0){
- labelmap[searchIndex] = labelIndex;
- PushQueue(queue, searchIndex);
- }
- }
- }
- int ConnectedComponentLabeling(unsigned char *bitmap, int width, int height, int *labelmap){
- int cx, cy, index, popIndex, labelIndex = 0;
- Queue *queue = NULL;
- queue = (Queue*)malloc(sizeof(Queue));
- queue->first = NULL;
- queue->last = NULL;
- memset(labelmap, 0, width * height);
- for(cy = 1; cy < height - 1; cy++){
- for(cx = 1; cx < width - 1; cx++){
- index = cy * width + cx;
- if(bitmap[index] == 255 && labelmap[index] == 0){
- labelIndex++;
- SearchNeighbor(bitmap, width, height, labelmap, labelIndex, index, queue);
- popIndex = PopQueue(queue);
- while(popIndex > -1){
- SearchNeighbor(bitmap, width, height, labelmap, labelIndex, popIndex, queue);
- popIndex = PopQueue(queue);
- }
- }
- }
- }
- free(queue);
- return labelIndex;
- }