F = VL_SIFT(I) computes the VL_SIFT frames (keypoints) F of the image I. I is a gray-scale image in single precision. Each column of F is a feature frame and has the format [X;Y;S;TH], where X,Y is the (fractional) center of the frame, S is the scale and TH is the orientation (in radians).
[F,D] = VL_SIFT(I) computes in addition the VL_SIFT descriptors D. Each column of D is the descriptor of the corresponding frame in F. A descriptor is a 128-dimensional vector of storage class UINT8.
Options:
- Octaves
Set the number of octave of the DoG scale space.
- Levels
Set the number of levels per octave of the DoG scale space.
- FirstOctave
Set the index of the first octave of the DoG scale space.
- PeakThresh
Set the peak selection threshold.
- EdgeThresh
Set the non-edge selection threshold.
- NormThresh
Set the minimum l2-norm of the descriptor before normalization. Descriptors below the threshold are set to zero.
- Magnif
Set the descriptor magnification factor. The scale of the keypoint is multiplied by this factor to obtain the width (in pixels) of the spatial bins. For instance, since by default there are 4 spatial bins along each spatial direction, the ``diameter'' of the descriptor is approximatively 4 * MAGNIF.
- Frames
Set the frames to use (bypass the detector). If frames are not passed in order of increasing scale, they are re-orderded.
- Orientations
Compute the orietantions of the frames overriding the orientation specified by the 'Frames' option.
- Verbose
Be verbose (may be repeated to increase the verbosity level).