cv2.kmeans在Python中的用法

Question

我正在考虑使用OpenCV的Kmeans实现，因为它说更快......

现在我正在使用包cv2和函数kmeans，

我无法理解参考中的参数说明：

Python: cv2.kmeans(data, K, criteria, attempts, flags[, bestLabels[, centers]]) → retval, bestLabels, centers
samples – Floating-point matrix of input samples, one row per sample.
clusterCount – Number of clusters to split the set by.
labels – Input/output integer array that stores the cluster indices for every sample.
criteria – The algorithm termination criteria, that is, the maximum number of iterations and/or the desired accuracy. The accuracy is specified as criteria.epsilon. As soon as each of the cluster centers moves by less than criteria.epsilon on some iteration, the algorithm stops.
attempts – Flag to specify the number of times the algorithm is executed using different initial labelings. The algorithm returns the labels that yield the best compactness (see the last function parameter).
flags –
Flag that can take the following values:
KMEANS_RANDOM_CENTERS Select random initial centers in each attempt.
KMEANS_PP_CENTERS Use kmeans++ center initialization by Arthur and Vassilvitskii [Arthur2007].
KMEANS_USE_INITIAL_LABELS During the first (and possibly the only) attempt, use the user-supplied labels instead of computing them from the initial centers. For the second and further attempts, use the random or semi-random centers. Use one of KMEANS_*_CENTERS flag to specify the exact method.
centers – Output matrix of the cluster centers, one row per each cluster center.

flags[, bestLabels[, centers]])的意思是什么意思？那他的那个：→ retval, bestLabels, centers？

这是我的代码：

import cv, cv2
import scipy.io
import numpy

# read data from .mat file
mat = scipy.io.loadmat('...')
keys = mat.keys()
values = mat.viewvalues()

data_1 = mat[keys[0]]
nRows = data_1.shape[1] 
nCols = data_1.shape[0]
samples = cv.CreateMat(nRows, nCols, cv.CV_32FC1)
labels = cv.CreateMat(nRows, 1, cv.CV_32SC1)
centers = cv.CreateMat(nRows, 100, cv.CV_32FC1)
#centers = numpy.

for i in range(0, nCols):
    for j in range(0, nRows):
        samples[j, i] = data_1[i, j]


cv2.kmeans(data_1.transpose,
                              100,
                              criteria=(cv2.TERM_CRITERIA_EPS | cv2.TERM_CRITERIA_MAX_ITER, 0.1, 10),
                              attempts=cv2.KMEANS_PP_CENTERS,
                              flags=cv2.KMEANS_PP_CENTERS,
)

我遇到这样的错误：

flags=cv2.KMEANS_PP_CENTERS,
TypeError: <unknown> is not a numpy array

我应该如何理解参数列表和cv2.kmeans的用法？感谢

Answer 1

几乎不可能找到关于此功能的文档。我写了下面的Python代码有点匆忙，但它适用于我的机器。它生成两个具有不同均值的多变量高斯分布，然后使用cv2.kmeans（）对它们进行分类。您可以参考this blog post来了解参数。

处理进口：

import cv
import cv2
import numpy as np
import numpy.random as r

生成一些随机点并适当地塑造它们：

samples = cv.CreateMat(50, 2, cv.CV_32FC1)
random_points = r.multivariate_normal((100,100), np.array([[150,400],[150,150]]), size=(25))
random_points_2 = r.multivariate_normal((300,300), np.array([[150,400],[150,150]]), size=(25))   
samples_list = np.append(random_points, random_points_2).reshape(50,2)  
random_points_list = np.array(samples_list, np.float32) 
samples = cv.fromarray(random_points_list)

绘制分类前后的点数：

blank_image = np.zeros((400,400,3))
blank_image_classified = np.zeros((400,400,3))

for point in random_points_list:
    cv2.circle(blank_image, (int(point[0]),int(point[1])), 1, (0,255,0),-1)

temp, classified_points, means = cv2.kmeans(data=np.asarray(samples), K=2, bestLabels=None,
criteria=(cv2.TERM_CRITERIA_EPS | cv2.TERM_CRITERIA_MAX_ITER, 1, 10), attempts=1, 
flags=cv2.KMEANS_RANDOM_CENTERS)   #Let OpenCV choose random centers for the clusters

for point, allocation in zip(random_points_list, classified_points):
    if allocation == 0:
        color = (255,0,0)
    elif allocation == 1:
        color = (0,0,255)
    cv2.circle(blank_image_classified, (int(point[0]),int(point[1])), 1, color,-1)

cv2.imshow("Points", blank_image)
cv2.imshow("Points Classified", blank_image_classified)
cv2.waitKey()

在这里你可以看到原始点：

以下是分类后的要点：

我希望这个答案可以帮到你，它不是k-means的完整指南，但它至少会告诉你如何将参数传递给OpenCV。

Answer 2

这里的问题是你的data_1.transpose不是一个numpy数组。

OpenCV 2.3.1及更高版本的python绑定不会将除numpy array之外的任何内容作为图像/数组参数。所以，data_1.transpose必须是一个numpy数组。

通常，OpenCV中的所有点都是numpy.ndarray

类型

例如

array([[[100., 433.]],
       [[157., 377.]],
       .
       .  
       [[147., 247.]], dtype=float32)

其中数组的每个元素都是

array([[100., 433.]], dtype=float32)

并且该数组的元素是

array([100., 433.], dtype=float32)