forked from 170010011/fr
349 lines
13 KiB
Python
349 lines
13 KiB
Python
|
import numpy as np
|
||
|
|
||
|
from ..feature.util import (FeatureDetector, DescriptorExtractor,
|
||
|
_mask_border_keypoints,
|
||
|
_prepare_grayscale_input_2D)
|
||
|
|
||
|
from ..feature import (corner_fast, corner_orientations, corner_peaks,
|
||
|
corner_harris)
|
||
|
from ..transform import pyramid_gaussian
|
||
|
from .._shared.utils import check_nD
|
||
|
|
||
|
from .orb_cy import _orb_loop
|
||
|
|
||
|
|
||
|
OFAST_MASK = np.zeros((31, 31))
|
||
|
OFAST_UMAX = [15, 15, 15, 15, 14, 14, 14, 13, 13, 12, 11, 10, 9, 8, 6, 3]
|
||
|
for i in range(-15, 16):
|
||
|
for j in range(-OFAST_UMAX[abs(i)], OFAST_UMAX[abs(i)] + 1):
|
||
|
OFAST_MASK[15 + j, 15 + i] = 1
|
||
|
|
||
|
|
||
|
class ORB(FeatureDetector, DescriptorExtractor):
|
||
|
|
||
|
"""Oriented FAST and rotated BRIEF feature detector and binary descriptor
|
||
|
extractor.
|
||
|
|
||
|
Parameters
|
||
|
----------
|
||
|
n_keypoints : int, optional
|
||
|
Number of keypoints to be returned. The function will return the best
|
||
|
`n_keypoints` according to the Harris corner response if more than
|
||
|
`n_keypoints` are detected. If not, then all the detected keypoints
|
||
|
are returned.
|
||
|
fast_n : int, optional
|
||
|
The `n` parameter in `skimage.feature.corner_fast`. Minimum number of
|
||
|
consecutive pixels out of 16 pixels on the circle that should all be
|
||
|
either brighter or darker w.r.t test-pixel. A point c on the circle is
|
||
|
darker w.r.t test pixel p if ``Ic < Ip - threshold`` and brighter if
|
||
|
``Ic > Ip + threshold``. Also stands for the n in ``FAST-n`` corner
|
||
|
detector.
|
||
|
fast_threshold : float, optional
|
||
|
The ``threshold`` parameter in ``feature.corner_fast``. Threshold used
|
||
|
to decide whether the pixels on the circle are brighter, darker or
|
||
|
similar w.r.t. the test pixel. Decrease the threshold when more
|
||
|
corners are desired and vice-versa.
|
||
|
harris_k : float, optional
|
||
|
The `k` parameter in `skimage.feature.corner_harris`. Sensitivity
|
||
|
factor to separate corners from edges, typically in range ``[0, 0.2]``.
|
||
|
Small values of `k` result in detection of sharp corners.
|
||
|
downscale : float, optional
|
||
|
Downscale factor for the image pyramid. Default value 1.2 is chosen so
|
||
|
that there are more dense scales which enable robust scale invariance
|
||
|
for a subsequent feature description.
|
||
|
n_scales : int, optional
|
||
|
Maximum number of scales from the bottom of the image pyramid to
|
||
|
extract the features from.
|
||
|
|
||
|
Attributes
|
||
|
----------
|
||
|
keypoints : (N, 2) array
|
||
|
Keypoint coordinates as ``(row, col)``.
|
||
|
scales : (N, ) array
|
||
|
Corresponding scales.
|
||
|
orientations : (N, ) array
|
||
|
Corresponding orientations in radians.
|
||
|
responses : (N, ) array
|
||
|
Corresponding Harris corner responses.
|
||
|
descriptors : (Q, `descriptor_size`) array of dtype bool
|
||
|
2D array of binary descriptors of size `descriptor_size` for Q
|
||
|
keypoints after filtering out border keypoints with value at an
|
||
|
index ``(i, j)`` either being ``True`` or ``False`` representing
|
||
|
the outcome of the intensity comparison for i-th keypoint on j-th
|
||
|
decision pixel-pair. It is ``Q == np.sum(mask)``.
|
||
|
|
||
|
References
|
||
|
----------
|
||
|
.. [1] Ethan Rublee, Vincent Rabaud, Kurt Konolige and Gary Bradski
|
||
|
"ORB: An efficient alternative to SIFT and SURF"
|
||
|
http://www.vision.cs.chubu.ac.jp/CV-R/pdf/Rublee_iccv2011.pdf
|
||
|
|
||
|
Examples
|
||
|
--------
|
||
|
>>> from skimage.feature import ORB, match_descriptors
|
||
|
>>> img1 = np.zeros((100, 100))
|
||
|
>>> img2 = np.zeros_like(img1)
|
||
|
>>> np.random.seed(1)
|
||
|
>>> square = np.random.rand(20, 20)
|
||
|
>>> img1[40:60, 40:60] = square
|
||
|
>>> img2[53:73, 53:73] = square
|
||
|
>>> detector_extractor1 = ORB(n_keypoints=5)
|
||
|
>>> detector_extractor2 = ORB(n_keypoints=5)
|
||
|
>>> detector_extractor1.detect_and_extract(img1)
|
||
|
>>> detector_extractor2.detect_and_extract(img2)
|
||
|
>>> matches = match_descriptors(detector_extractor1.descriptors,
|
||
|
... detector_extractor2.descriptors)
|
||
|
>>> matches
|
||
|
array([[0, 0],
|
||
|
[1, 1],
|
||
|
[2, 2],
|
||
|
[3, 3],
|
||
|
[4, 4]])
|
||
|
>>> detector_extractor1.keypoints[matches[:, 0]]
|
||
|
array([[42., 40.],
|
||
|
[47., 58.],
|
||
|
[44., 40.],
|
||
|
[59., 42.],
|
||
|
[45., 44.]])
|
||
|
>>> detector_extractor2.keypoints[matches[:, 1]]
|
||
|
array([[55., 53.],
|
||
|
[60., 71.],
|
||
|
[57., 53.],
|
||
|
[72., 55.],
|
||
|
[58., 57.]])
|
||
|
|
||
|
"""
|
||
|
|
||
|
def __init__(self, downscale=1.2, n_scales=8,
|
||
|
n_keypoints=500, fast_n=9, fast_threshold=0.08,
|
||
|
harris_k=0.04):
|
||
|
self.downscale = downscale
|
||
|
self.n_scales = n_scales
|
||
|
self.n_keypoints = n_keypoints
|
||
|
self.fast_n = fast_n
|
||
|
self.fast_threshold = fast_threshold
|
||
|
self.harris_k = harris_k
|
||
|
|
||
|
self.keypoints = None
|
||
|
self.scales = None
|
||
|
self.responses = None
|
||
|
self.orientations = None
|
||
|
self.descriptors = None
|
||
|
|
||
|
def _build_pyramid(self, image):
|
||
|
image = _prepare_grayscale_input_2D(image)
|
||
|
return list(pyramid_gaussian(image, self.n_scales - 1,
|
||
|
self.downscale, multichannel=False))
|
||
|
|
||
|
def _detect_octave(self, octave_image):
|
||
|
dtype = octave_image.dtype
|
||
|
# Extract keypoints for current octave
|
||
|
fast_response = corner_fast(octave_image, self.fast_n,
|
||
|
self.fast_threshold)
|
||
|
keypoints = corner_peaks(fast_response, min_distance=1)
|
||
|
|
||
|
if len(keypoints) == 0:
|
||
|
return (np.zeros((0, 2), dtype=dtype),
|
||
|
np.zeros((0, ), dtype=dtype),
|
||
|
np.zeros((0, ), dtype=dtype))
|
||
|
|
||
|
mask = _mask_border_keypoints(octave_image.shape, keypoints,
|
||
|
distance=16)
|
||
|
keypoints = keypoints[mask]
|
||
|
|
||
|
orientations = corner_orientations(octave_image, keypoints,
|
||
|
OFAST_MASK)
|
||
|
|
||
|
harris_response = corner_harris(octave_image, method='k',
|
||
|
k=self.harris_k)
|
||
|
responses = harris_response[keypoints[:, 0], keypoints[:, 1]]
|
||
|
|
||
|
return keypoints, orientations, responses
|
||
|
|
||
|
def detect(self, image):
|
||
|
"""Detect oriented FAST keypoints along with the corresponding scale.
|
||
|
|
||
|
Parameters
|
||
|
----------
|
||
|
image : 2D array
|
||
|
Input image.
|
||
|
|
||
|
"""
|
||
|
check_nD(image, 2)
|
||
|
|
||
|
pyramid = self._build_pyramid(image)
|
||
|
|
||
|
keypoints_list = []
|
||
|
orientations_list = []
|
||
|
scales_list = []
|
||
|
responses_list = []
|
||
|
|
||
|
for octave in range(len(pyramid)):
|
||
|
|
||
|
octave_image = np.ascontiguousarray(pyramid[octave])
|
||
|
|
||
|
keypoints, orientations, responses = self._detect_octave(
|
||
|
octave_image)
|
||
|
|
||
|
keypoints_list.append(keypoints * self.downscale ** octave)
|
||
|
orientations_list.append(orientations)
|
||
|
scales_list.append(np.full(
|
||
|
keypoints.shape[0], self.downscale ** octave,
|
||
|
dtype=octave_image.dtype))
|
||
|
responses_list.append(responses)
|
||
|
|
||
|
keypoints = np.vstack(keypoints_list)
|
||
|
orientations = np.hstack(orientations_list)
|
||
|
scales = np.hstack(scales_list)
|
||
|
responses = np.hstack(responses_list)
|
||
|
|
||
|
if keypoints.shape[0] < self.n_keypoints:
|
||
|
self.keypoints = keypoints
|
||
|
self.scales = scales
|
||
|
self.orientations = orientations
|
||
|
self.responses = responses
|
||
|
else:
|
||
|
# Choose best n_keypoints according to Harris corner response
|
||
|
best_indices = responses.argsort()[::-1][:self.n_keypoints]
|
||
|
self.keypoints = keypoints[best_indices]
|
||
|
self.scales = scales[best_indices]
|
||
|
self.orientations = orientations[best_indices]
|
||
|
self.responses = responses[best_indices]
|
||
|
|
||
|
def _extract_octave(self, octave_image, keypoints, orientations):
|
||
|
mask = _mask_border_keypoints(octave_image.shape, keypoints,
|
||
|
distance=20)
|
||
|
keypoints = np.array(keypoints[mask], dtype=np.intp, order='C',
|
||
|
copy=False)
|
||
|
orientations = np.array(orientations[mask], order='C',
|
||
|
copy=False)
|
||
|
|
||
|
descriptors = _orb_loop(octave_image, keypoints, orientations)
|
||
|
|
||
|
return descriptors, mask
|
||
|
|
||
|
def extract(self, image, keypoints, scales, orientations):
|
||
|
"""Extract rBRIEF binary descriptors for given keypoints in image.
|
||
|
|
||
|
Note that the keypoints must be extracted using the same `downscale`
|
||
|
and `n_scales` parameters. Additionally, if you want to extract both
|
||
|
keypoints and descriptors you should use the faster
|
||
|
`detect_and_extract`.
|
||
|
|
||
|
Parameters
|
||
|
----------
|
||
|
image : 2D array
|
||
|
Input image.
|
||
|
keypoints : (N, 2) array
|
||
|
Keypoint coordinates as ``(row, col)``.
|
||
|
scales : (N, ) array
|
||
|
Corresponding scales.
|
||
|
orientations : (N, ) array
|
||
|
Corresponding orientations in radians.
|
||
|
|
||
|
"""
|
||
|
check_nD(image, 2)
|
||
|
|
||
|
pyramid = self._build_pyramid(image)
|
||
|
|
||
|
descriptors_list = []
|
||
|
mask_list = []
|
||
|
|
||
|
# Determine octaves from scales
|
||
|
octaves = (np.log(scales) / np.log(self.downscale)).astype(np.intp)
|
||
|
|
||
|
for octave in range(len(pyramid)):
|
||
|
|
||
|
# Mask for all keypoints in current octave
|
||
|
octave_mask = octaves == octave
|
||
|
|
||
|
if np.sum(octave_mask) > 0:
|
||
|
|
||
|
octave_image = np.ascontiguousarray(pyramid[octave])
|
||
|
|
||
|
octave_keypoints = keypoints[octave_mask]
|
||
|
octave_keypoints /= self.downscale ** octave
|
||
|
octave_orientations = orientations[octave_mask]
|
||
|
|
||
|
descriptors, mask = self._extract_octave(octave_image,
|
||
|
octave_keypoints,
|
||
|
octave_orientations)
|
||
|
|
||
|
descriptors_list.append(descriptors)
|
||
|
mask_list.append(mask)
|
||
|
|
||
|
self.descriptors = np.vstack(descriptors_list).view(bool)
|
||
|
self.mask_ = np.hstack(mask_list)
|
||
|
|
||
|
def detect_and_extract(self, image):
|
||
|
"""Detect oriented FAST keypoints and extract rBRIEF descriptors.
|
||
|
|
||
|
Note that this is faster than first calling `detect` and then
|
||
|
`extract`.
|
||
|
|
||
|
Parameters
|
||
|
----------
|
||
|
image : 2D array
|
||
|
Input image.
|
||
|
|
||
|
"""
|
||
|
check_nD(image, 2)
|
||
|
|
||
|
pyramid = self._build_pyramid(image)
|
||
|
|
||
|
keypoints_list = []
|
||
|
responses_list = []
|
||
|
scales_list = []
|
||
|
orientations_list = []
|
||
|
descriptors_list = []
|
||
|
|
||
|
for octave in range(len(pyramid)):
|
||
|
|
||
|
octave_image = np.ascontiguousarray(pyramid[octave])
|
||
|
|
||
|
keypoints, orientations, responses = self._detect_octave(
|
||
|
octave_image)
|
||
|
|
||
|
if len(keypoints) == 0:
|
||
|
keypoints_list.append(keypoints)
|
||
|
responses_list.append(responses)
|
||
|
descriptors_list.append(np.zeros((0, 256), dtype=bool))
|
||
|
continue
|
||
|
|
||
|
descriptors, mask = self._extract_octave(octave_image, keypoints,
|
||
|
orientations)
|
||
|
|
||
|
scaled_keypoints = keypoints[mask] * self.downscale ** octave
|
||
|
keypoints_list.append(scaled_keypoints)
|
||
|
responses_list.append(responses[mask])
|
||
|
orientations_list.append(orientations[mask])
|
||
|
scales_list.append(self.downscale ** octave *
|
||
|
np.ones(scaled_keypoints.shape[0], dtype=np.intp))
|
||
|
descriptors_list.append(descriptors)
|
||
|
|
||
|
if len(scales_list) == 0:
|
||
|
raise RuntimeError(
|
||
|
"ORB found no features. Try passing in an image containing "
|
||
|
"greater intensity contrasts between adjacent pixels.")
|
||
|
|
||
|
keypoints = np.vstack(keypoints_list)
|
||
|
responses = np.hstack(responses_list)
|
||
|
scales = np.hstack(scales_list)
|
||
|
orientations = np.hstack(orientations_list)
|
||
|
descriptors = np.vstack(descriptors_list).view(bool)
|
||
|
|
||
|
if keypoints.shape[0] < self.n_keypoints:
|
||
|
self.keypoints = keypoints
|
||
|
self.scales = scales
|
||
|
self.orientations = orientations
|
||
|
self.responses = responses
|
||
|
self.descriptors = descriptors
|
||
|
else:
|
||
|
# Choose best n_keypoints according to Harris corner response
|
||
|
best_indices = responses.argsort()[::-1][:self.n_keypoints]
|
||
|
self.keypoints = keypoints[best_indices]
|
||
|
self.scales = scales[best_indices]
|
||
|
self.orientations = orientations[best_indices]
|
||
|
self.responses = responses[best_indices]
|
||
|
self.descriptors = descriptors[best_indices]
|