OpenCV PCA Compute in Python

问题:

I'm loading a set of test images via OpenCV (in Python) which are 128x128 in size, reshape them into vectors (1, 128x128) and put them all together in a matrix to calculate PCA. I'm using the new cv2 libaries...

The code:

import os import cv2 as cv import numpy as np  matrix_test = None for image in os.listdir('path_to_dir'):     imgraw = cv.imread(os.path.join('path_to_dir', image), 0)     imgvector = imgraw.reshape(128*128)     try:         matrix_test = np.vstack((matrix_test, imgvector))     except:         matrix_test = imgvector  # PCA mean, eigenvectors = cv.PCACompute(matrix_test, np.mean(matrix_test, axis=0)) 

And it allways fails on the PCA part (I tested the image loading and all, the resulting matrix is how it should be)...the error I get is:

File "main.py", line 22, in

mean, eigenvectors = cv.PCACompute(matrix_test, np.mean(matri_test, axis=0))

cv2.error: /path/to/OpenCV-2.3.1/modules/core/src/matmul.cpp:2781: error: (-215) _mean.size() == mean_sz in function operator()

回答1:

I think the problem is with the size of

np.mean(matrix_test, axis=0) 

Its size is (128x128,) and not (1, 128x128). Thus the code below should work

mean, eigenvectors = cv.PCACompute(matrix_test, np.mean(matrix_test, axis=0).reshape(1,-1)) 

回答2:

You can also put

cv.PCACompute(matrix_test, mean = np.array([])) 

and the function computes the mean.

文章来源: OpenCV PCA Compute in Python