Matlab: reshape 4-d matrix to 2-d and maintain order, how to?

Question

I'm trying yo implement vlsh with the California ND Datastet, wich is composed by 701 photos. 10 subject wrote down in a txt file which photos are near duplicate for them, and we have also correlation matrix. The images are RGB and i reduced them in 20x20. I created a 4-d array 20x20x3x701. So i tried to reshape and obtained a 1200x701 matrix, but the problem is that reshape can't maintain the order of the original matrix. I tried to search online and most of suggestion is to use "Permute", but it seems to me that doesn't fit my situation.

I can post the matlab code:

`
path='C:\Users\franc\Desktop\stage\californiaND\prova*.jpg';
path2='C:\Users\franc\Desktop\stage\californiaND\prova';
d=dir(path);
a=[];
for m=1:length(d)
  a=cat(4,a,imread(strcat(path2,d(m).name)));
end
r=reshape(a,[],701);
r=double(r);
L = lshConstruct( r, 10,4);`

What is the order you'd want your data to be with respect to the input? — BillBokeey
I want that every matrix of the same image is concatenated. So one matrix of 1200 pixel, for 701 images. — FireFox1616
Yes, but in what order should the 2nd and 3rd dimensions be collapsed into the 1st dimension? Reshape doesn't randomise the order... — Wolfie
It looks like the problem is that you crate a 4D matrix.... just create what you want from the start, not from the 4D matrix — Ander Biguri
@AnderBiguri How can i do it? i have 2-d matrix in 3 channel. I have to reshape anyway, or at least i think. Can you help me? thank you anyway — FireFox1616

Ander Biguri Ander Biguri · Accepted Answer · 2017-08-23T11:37:40

I am assuming you need the 1D vector in RGBRGB format, as otherwise the solution would be trivial ( just (:)).

Assuming imread is reading 20x20x3 images one by one, this is how you directly make your 2D matrix:

for m=1:length(d) % this is 701, right?
  im=imread(strcat(path2,d(m).name));
  im=permute(im,[3 1 2]);
  a=cat(2,im(:));
end

Matlab: reshape 4-d matrix to 2-d and maintain order, how to?

1 Answers