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sift.h
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sift.h
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/**@file
Functions for detecting SIFT image features.
For more information, refer to:
Lowe, D. Distinctive image features from scale-invariant keypoints.
<EM>International Journal of Computer Vision, 60</EM>, 2 (2004),
pp.91--110.
@author Rob Hess
@version 1.1.0-20060711
*/
#ifndef SIFT_H
#define SIFT_H
#include "cxcore.h"
/******************************** Structures *********************************/
/** holds feature data relevant to detection */
struct detection_data
{
int r;
int c;
int octv;
int intvl;
double subintvl;
double scl_octv;
};
struct feature;
/******************************* Defs and macros *****************************/
/** default number of sampled intervals per octave */
#define SIFT_INTVLS 3
/** default sigma for initial gaussian smoothing */
#define SIFT_SIGMA 1.6
/** default threshold on keypoint contrast |D(x)| */
#define SIFT_CONTR_THR 0.04
/** default threshold on keypoint ratio of principle curvatures */
#define SIFT_CURV_THR 10
/** double image size before pyramid construction? */
#define SIFT_IMG_DBL 1
/** default width of descriptor histogram array */
#define SIFT_DESCR_WIDTH 4
/** default number of bins per histogram in descriptor array */
#define SIFT_DESCR_HIST_BINS 8
/* assumed gaussian blur for input image */
#define SIFT_INIT_SIGMA 0.5
/* width of border in which to ignore keypoints */
#define SIFT_IMG_BORDER 5
/* maximum steps of keypoint interpolation before failure */
#define SIFT_MAX_INTERP_STEPS 5
/* default number of bins in histogram for orientation assignment */
#define SIFT_ORI_HIST_BINS 36
/* determines gaussian sigma for orientation assignment */
#define SIFT_ORI_SIG_FCTR 1.5
/* determines the radius of the region used in orientation assignment */
#define SIFT_ORI_RADIUS 3.0 * SIFT_ORI_SIG_FCTR
/* number of passes of orientation histogram smoothing */
#define SIFT_ORI_SMOOTH_PASSES 2
/* orientation magnitude relative to max that results in new feature */
#define SIFT_ORI_PEAK_RATIO 0.8
/* determines the size of a single descriptor orientation histogram */
#define SIFT_DESCR_SCL_FCTR 3.0
/* threshold on magnitude of elements of descriptor vector */
#define SIFT_DESCR_MAG_THR 0.2
/* factor used to convert floating-point descriptor to unsigned char */
#define SIFT_INT_DESCR_FCTR 512.0
/* returns a feature's detection data */
#define feat_detection_data(f) ( (struct detection_data*)(f->feature_data) )
/*************************** Function Prototypes *****************************/
/**
Finds SIFT features in an image using default parameter values. All
detected features are stored in the array pointed to by \a feat.
@param img the image in which to detect features
@param feat a pointer to an array in which to store detected features
@return Returns the number of features stored in \a feat or -1 on failure
@see _sift_features()
*/
extern int sift_features( IplImage* img, struct feature** feat );
/**
Finda SIFT features in an image using user-specified parameter values. All
detected features are stored in the array pointed to by \a feat.
@param img the image in which to detect features
@param feat a pointer to an array in which to store detected features
@param intvls the number of intervals sampled per octave of scale space
@param sigma the amount of Gaussian smoothing applied to each image level
before building the scale space representation for an octave
@param contr_thr a threshold on the value of the scale space function
\f$\left|D(\hat{x})\right|\f$, where \f$\hat{x}\f$ is a vector specifying
feature location and scale, used to reject unstable features; assumes
pixel values in the range [0, 1]
@param curv_thr threshold on a feature's ratio of principle curvatures
used to reject features that are too edge-like
@param img_dbl should be 1 if image doubling prior to scale space
construction is desired or 0 if not
@param descr_width the width, \f$n\f$, of the \f$n \times n\f$ array of
orientation histograms used to compute a feature's descriptor
@param descr_hist_bins the number of orientations in each of the
histograms in the array used to compute a feature's descriptor
@return Returns the number of keypoints stored in \a feat or -1 on failure
@see sift_features()
*/
extern int _sift_features( IplImage* img, struct feature** feat, int intvls,
double sigma, double contr_thr, int curv_thr,
int img_dbl, int descr_width, int descr_hist_bins );
#endif