/*
Computes feature descriptors for features in an array. Based on Section 6
of Lowe's paper.
@param features array of features
@param gauss_pyr Gaussian scale space pyramid
@param d width of 2D array of orientation histograms
@param n number of bins per orientation histogram
*/
void compute_descriptors( CvSeq* features, IplImage*** gauss_pyr, int d, int n)
{
struct feature* feat;
struct detection_data* ddata;
double*** hist;
int i, k = features->total;
for( i = 0; i < k; i++ )
{
feat = CV_GET_SEQ_ELEM( struct feature, features, i );
ddata = feat_detection_data( feat );
hist = descr_hist( gauss_pyr[ddata->octv][ddata->intvl], ddata->r,
ddata->c, feat->ori, ddata->scl_octv, d, n );
hist_to_descr( hist, d, n, feat );
release_descr_hist( &hist, d );
}
}
/*
Computes feature descriptors for features in an array. Based on Section 6 of Lowe's paper.
@param features array of features
@param gauss_pyr Gaussian scale space pyramid
@param d width of 2D array of orientation histograms
@param n number of bins per orientation histogram
*/
static void compute_descriptors( CvSeq* features, IplImage*** gauss_pyr, int d, int n)
{
struct feature* feat;
struct detection_data* ddata;
double*** hist;//d*d*n的三维直方图数组
int i, k = features->total;//特征点的个数
//遍历特征点序列中的特征点
for( i = 0; i < k; i++ )
{
//调用宏，获取序列features中的第i个元素，并强制转换为struct feature类型
feat = CV_GET_SEQ_ELEM( struct feature, features, i );
//调用宏feat_detection_data来提取参数feat中的feature_data成员并转换为detection_data类型的指针
ddata = feat_detection_data( feat );
//计算特征点附近区域的方向直方图，此直方图在计算特征描述子中要用到，返回值是一个d*d*n的三维数组
hist = descr_hist( gauss_pyr[ddata->octv][ddata->intvl], ddata->r,
ddata->c, feat->ori, ddata->scl_octv, d, n );
//将某特征点的方向直方图转换为特征描述子向量，对特征描述子归一化并将所有元素转化为整型，存入特征点feat中
hist_to_descr( hist, d, n, feat );
//释放特征点的方向直方图
release_descr_hist( &hist, d );
}
}