[英]OpenCV: Extract SURF Features from user-defined keypoints
我想从指定的关键点计算SURF功能。 我正在使用OpenCV的Python包装器。 以下是我尝试使用的代码,但是在任何地方都找不到有效的示例。
surf = cv2.SURF()
keypoints, descriptors = surf.detect(np.asarray(image[:,:]),None,useProvidedKeypoints = True)
如何指定此功能要使用的关键点?
相似的,未解决的问题: useProvidedKeypoints = true时cvExtractSURF不起作用
如果我正确理解了Python绑定的源代码,则在Python绑定中永远不会使用C ++接口中存在的“ keypoints”参数。 因此,我警告您无法对当前绑定执行您要尝试的操作。 一种可能的解决方案是编写您自己的绑定。 我知道这不是你希望的答案...
尝试为此使用cv2.DescriptorMatcher_create。
例如,在下面的代码中,我正在使用pylab,但是您可以获得消息;)
它使用GFTT计算关键点,然后使用SURF描述符和蛮力匹配。 每个代码部分的输出显示为标题。
%pylab inline
import cv2
import numpy as np
img = cv2.imread('./img/nail.jpg')
gray= cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
imshow(gray, cmap=cm.gray)
输出是这样的http://i.stack.imgur.com/8eOTe.png
(对于本示例,我将作弊并使用相同的图像来获取关键点和描述符)。
img1 = gray
img2 = gray
detector = cv2.FeatureDetector_create("GFTT")
descriptor = cv2.DescriptorExtractor_create("SURF")
matcher = pt1=(int(k1[m.queryIdx].pt[0]),int(k1[m.queryIdx].pt[1]))("FlannBased")
# detect keypoints
kp1 = detector.detect(img1)
kp2 = detector.detect(img2)
print '#keypoints in image1: %d, image2: %d' % (len(kp1), len(kp2))
# descriptors
k1, d1 = descriptor.compute(img1, kp1)
k2, d2 = descriptor.compute(img2, kp2)
print '#Descriptors size in image1: %s, image2: %s' % ((d1.shape), (d2.shape))
# match the keypoints
matches = matcher.match(d1,d2)
# visualize the matches
print '#matches:', len(matches)
dist = [m.distance for m in matches]
print 'distance: min: %.3f' % min(dist)
print 'distance: mean: %.3f' % (sum(dist) / len(dist))
print 'distance: max: %.3f' % max(dist)
距离:最小:0.000
距离:平均值:0.000
距离:最大:0.000
# threshold: half the mean
thres_dist = (sum(dist) / len(dist)) * 0.5 + 0.5
# keep only the reasonable matches
sel_matches = [m for m in matches if m.distance < thres_dist]
print '#selected matches:', len(sel_matches)
#Plot
h1, w1 = img1.shape[:2]
h2, w2 = img2.shape[:2]
view = zeros((max(h1, h2), w1 + w2, 3), uint8)
view[:h1, :w1, 0] = img1
view[:h2, w1:, 0] = img2
view[:, :, 1] = view[:, :, 0]
view[:, :, 2] = view[:, :, 0]
for m in sel_matches:
# draw the keypoints
# print m.queryIdx, m.trainIdx, m.distance
color = tuple([random.randint(0, 255) for _ in xrange(3)])
pt1=(int(k1[m.queryIdx].pt[0]),int(k1[m.queryIdx].pt[1]))
pt2=(int(k2[m.queryIdx].pt[0]+w1),int(k2[m.queryIdx].pt[1]))
cv2.line(view,pt1,pt2,color)
如何使用上述Mahotas
完成此操作的Mahotas
:
import mahotas
from mahotas.features import surf
import numpy as np
def process_image(imagename):
'''Process an image and returns descriptors and keypoints location'''
# Load the images
f = mahotas.imread(imagename, as_grey=True)
f = f.astype(np.uint8)
spoints = surf.dense(f, spacing=12, include_interest_point=True)
# spoints includes both the detection information (such as the position
# and the scale) as well as the descriptor (i.e., what the area around
# the point looks like). We only want to use the descriptor for
# clustering. The descriptor starts at position 5:
desc = spoints[:, 5:]
kp = spoints[:, :2]
return kp, desc
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