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# import the necessary packages
from __future__ import absolute_import
import numpy as np
import cv2
from ..convenience import is_cv2
class RootSIFT:
def __init__(self):
# initialize the SIFT feature extractor for OpenCV 2.4
if is_cv2():
self.extractor = cv2.DescriptorExtractor_create("SIFT")
# otherwise initialize the SIFT feature extractor for OpenCV 3+
else:
self.extractor = cv2.xfeatures2d.SIFT_create()
def compute(self, image, kps, eps=1e-7):
# compute SIFT descriptors
(kps, descs) = self.extractor.compute(image, kps)
# if there are no keypoints or descriptors, return an empty tuple
if len(kps) == 0:
return ([], None)
# apply the Hellinger kernel by first L1-normalizing and taking the
# square-root
descs /= (descs.sum(axis=1, keepdims=True) + eps)
descs = np.sqrt(descs)
# return a tuple of the keypoints and descriptors
return (kps, descs)
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