/*
Converts the 2D array of orientation histograms into a feature's descriptor vector.
@param hist 2D array of orientation histograms
@param d width of hist
@param n bins per histogram
@param feat feature into which to store descriptor
*/
static void hist_to_descr( double*** hist, int d, int n, struct feature* feat )
{
int int_val, i, r, c, o, k = 0;
//遍历d*d*n的三维直方图数组，将其中的所有数据(一般是128个)都存入feat结构的descr成员中
for( r = 0; r < d; r++ )
for( c = 0; c < d; c++ )
for( o = 0; o < n; o++ )
feat->descr[k++] = hist[r][c][o];
feat->d = k;//特征描述子的维数，一般是128
//归一化特征点的特征描述子，即将特征描述子数组中每个元素除以特征描述子的模
normalize_descr( feat );
//遍历特征描述子向量，将超过阈值SIFT_DESCR_MAG_THR的元素强行赋值为SIFT_DESCR_MAG_THR
for( i = 0; i < k; i++ )
if( feat->descr[i] > SIFT_DESCR_MAG_THR )
feat->descr[i] = SIFT_DESCR_MAG_THR;
//再次归一化特征描述子向量
normalize_descr( feat );
/* convert floating-point descriptor to integer valued descriptor */
//遍历特征描述子向量，每个元素乘以系数SIFT_INT_DESCR_FCTR来变为整型，并且最大值不能超过255
for( i = 0; i < k; i++ )
{
int_val = SIFT_INT_DESCR_FCTR * feat->descr[i];
feat->descr[i] = MIN( 255, int_val );
}
}
/*
Converts the 2D array of orientation histograms into a feature's descriptor
vector.
@param hist 2D array of orientation histograms
@param d width of hist
@param n bins per histogram
@param feat feature into which to store descriptor
*/
void hist_to_descr( double*** hist, int d, int n, struct feature* feat )
{
int int_val, i, r, c, o, k = 0;
for( r = 0; r < d; r++ )
for( c = 0; c < d; c++ )
for( o = 0; o < n; o++ )
feat->descr[k++] = hist[r][c][o];
feat->d = k;
normalize_descr( feat );
for( i = 0; i < k; i++ )
if( feat->descr[i] > SIFT_DESCR_MAG_THR )
feat->descr[i] = SIFT_DESCR_MAG_THR;
normalize_descr( feat );
/* convert floating-point descriptor to integer valued descriptor */
for( i = 0; i < k; i++ )
{
int_val = SIFT_INT_DESCR_FCTR * feat->descr[i];
feat->descr[i] = MIN( 255, int_val );
}
}
