switching pixel with defined colour in a matrix

Question

Gemma 2014-11-17

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https://ww2.mathworks.cn/matlabcentral/answers/163071-switching-pixel-with-defined-colour-in-a-matrix

回答： Image Analyst 2014-11-18

Hello everybody,

I would like to shuffle single pixels (or even better: groups of pixels) of an image. Important is that every pixel keeps its colour information, so that in the end, the values of pixels of one certain colour is constant.

I know how to do that with a normal matrix. But when it is about colour-values, I have 3 linked matrices (in the RGB-colour-range). How is it possible to combine the 3 matrices with the same grade of permutation?

Or is it possible to select the n-th permutation of a matrix and reshaping it? is that n-th permutation of matrix a in the same way permuted like the n-th permutation of matrix b?

I hope I made myself clear and that somebody could help.

Thank you in advance

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Answer 1

Evan 2014-11-17

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编辑：Evan 2014-11-17

在 MATLAB Online 中打开

If I is your image:

I = imread('peppers.png');
R = I(:,:,1);
G = I(:,:,2);
B = I(:,:,3);
Idx = reshape(randperm(numel(R)),size(R));
R = R(Idx); G = G(Idx); B = B(Idx);
I_new = cat(3,R,G,B);
% Visualize the images.
subplot(1,2,1); imagesc(I); title('Before'); axis image
subplot(1,2,2); imagesc(I_new); title('After'); axis image
% Test to see that pixels have only been re-ordered, not changed.
sum(I(:)) == sum(I_new(:))

Also, it looks like there are some tools on the file exchange that allow you to "scramble" images in more sophisticated ways:

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Gemma 2014-11-17

Hello Evan,

That's awesome! =) Until now I played around and got this:

I = imread('3mal3.png'); imshow(I)

R = I(:,:,1) G = I(:,:,2) B = I(:,:,3)

% permutation R perm_R = perms(R(:)) subset_R = perm_R(4, :) nteMatrix_R = reshape(subset_R,3,3) % permutation G perm_G = perms(G(:)) subset_G = perm_G(4, :) nteMatrix_G = reshape(subset_G,3,3) % permutation B perm_B = perms(B(:)) subset_B = perm_B(4, :) nteMatrix_B = reshape(subset_B,3,3)

%% Wieder zu RGB zusammensetzen nteMatrix_R=R nteMatrix_G=G nteMatrix_B=B

At that moment when I was trying to combine my RGB-values in one image again, you answered! And your skript is very much better, because mine needs so much time for running! Thank you very much! :)

Evan 2014-11-17

No problem. Glad it's working for you!

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Answer 2

Image Analyst 2014-11-18

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/163071-switching-pixel-with-defined-colour-in-a-matrix#answer_159294

scramble_image.m

For whatever it's worth (now that you've accepted a working example), I attach my demo (below the image it creates). (I was traveling the last two days and I didn't see this until now.)