我有一些python代码来比较两个图像：
detector_FeatureDetector_1 = cv2.FastFeatureDetector_create()
detector_FeatureDetector_2 = cv2.FastFeatureDetector_create()
detector_DescriptorExtractor_1 = cv2.BRISK_create()
detector_DescriptorExtractor_2 = cv2.BRISK_create()
detector_DescriptorMatcher_1 = cv2.BFMatcher(cv2.NORM_HAMMING2, crossCheck = True)
detector_DescriptorMatcher_2 = cv2.BFMatcher(cv2.NORM_HAMMING2, crossCheck = True)
image_1 = cv2.imread('/Users/rui/image1.png')
image_2 = cv2.imread('/Users/rui/image2.png')
obj_descriptor_keypoints_1 = detector_FeatureDetector.detect(image_1)
obj_descriptor_keypoints_2 = detector_FeatureDetector.detect(image_2)
keypoints1, obj_descriptor_descriptors_1 = detector_DescriptorExtractor.compute(image_1, obj_descriptor_keypoints_1)
keypoints2, obj_descriptor_descriptors_2 = detector_DescriptorExtractor.compute(image_2, obj_descriptor_keypoints_2)
matches = detector_DescriptorMatcher.knnMatch(obj_descriptor_descriptors_1, obj_descriptor_descriptors_2, k=6)
但detector_DescriptorMatcher.knnMatch()仅适用于k=1。如果k的值与1不同，则会返回以下错误：
OpenCV Error: Assertion failed (K == 1 && update == 0 && mask.empty()) in batchDistance, file /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_graphics_opencv/opencv/work/opencv-3.0.0/modules/core/src/stat.cpp, line 3682
Traceback (most recent call last):
File "/Users/rui/main.py", line 191, in <module>
matches = detector_DescriptorMatcher.knnMatch(obj_descriptor_descriptors, obj_descriptor_descriptors_movie_frame, k=6)
cv2.error: /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_graphics_opencv/opencv/work/opencv-3.0.0/modules/core/src/stat.cpp:3682: error: (-215) K == 1 && update == 0 && mask.empty() in function batchDistance
答案 0 :(得分：7)
使用extension NSManagedObject {
func safeSetValue(value : AnyObject, forKey key : String) -> Bool {
// Get NSAttributeDescription for key:
guard let attr = self.entity.attributesByName[key] else {
return false
}
// Get name of the class used to represent the attribute:
guard let cname = attr.attributeValueClassName else {
return false
}
// Create class object from name:
guard let cls : AnyClass = NSClassFromString(cname) else {
return false
}
// Check if given value is an instance of a subclass:
if !value.isKindOfClass(cls) {
return false
}
// Finally: Set value for key:
self.setValue(value, forKey: key)
return true
}
}
配置BFMatcher会导致错误。对于crossCheck = True，请设置k > 1（构造函数默认值）。
来自docs：
如果
crossCheck = False，那么带有crossCheck==true的{{1}}方法只返回knnMatch()对，以便k=1查询描述符(i,j)描述符在匹配器的集合中是最接近的，反之亦然，即i-th将只返回一致的对。当有足够的匹配时，这种技术通常产生最佳结果，并且具有最少数量的异常值。这是D. Lowe在SIFT论文中使用的比率测试的替代方案。