What is the equivalent python code for this octave code - python-2.7

Question

link to code and files
1.I =imread('one.jpg');
2.I = inresize(I,[20,20]);
3.I=im2double(I);
4.I=mean(I,3);
#This next line
5.a = reshape(I,[],400);
I read an image and resizzed it to 20*20 and then converted it to matrix and then find the grayscale .All this I can do in Python too....but I can't do the 5 th line of code...if I tried ,
reshape (I,1,400)...the image appears rotated...I don't know how to write the 5 the line as above in python
The problem
in the link along with the code theres is a displayData function.I saved the matrix i got using python as mat and loaded it on octave when i called displayData() on the matrix i got a rotated image.thats inclued in the link.And theres no such problem in octave.Thank you for looking into this.

Answer 1

For reshaping an array you can use numpy, and, following your code, you can use reshape. In your case, you are changing the size of I, from (20,20) to (1,400).
A complete example which saves the resulting reshaped array to a mat file, using OpenCV APIs for dealing with images, is:
import numpy as np
import cv2
import scipy.io
I = cv2.imread('one.jpg')
I = cv2.resize(I,(20,20))
I = cv2.normalize(I.astype('float'), None, 0.0, 1.0, cv2.NORM_MINMAX)
I = np.mean(I, axis=2)
a = np.reshape(I, (1,400), order='F')
scipy.io.savemat('a.mat', mdict={'a': a})
Note the second parameter of reshape, which is a tuple containing the new size of the array. Also, notice the third parameter order that allows to rearrange elements in column-major style (Fortran) which is the convention used by octave (see reshape in octave http://www.gnu.org/software/octave/doc/v4.0.1/Rearranging-Matrices.html#XREFreshape). This results in a correct image, non rotated, compared to the one got from octave.
However, given the fact that you want to get from a 2d array a 1d array, you can use, from numpy, ravel if you want to get a view of I (when possible), namely a modification of a changes also I; or flatten, which returns a copy of I, thus modifying a does not change I. However, note that both ravel and flatten returns a 1d array resulting in a size of (400,). The same order parameter should be used.