How can I simplify my code using loops?

Below is my code for image processing

I'd like to simplify the underlined area of my code using loops, but I don't know how to do it.

Is there anyone to help me?

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clc;

clear all;

lena=imread('lena.ppm');

lena_ch1=lena(:,:,1);

% The first of unknown channels

lena_ch2=lena(:,:,2);

% The second of unknown channels

lena_ch3=lena(:,:,3);

% The third of unknown channels

black_ch=zeros(size(lena,1),size(lena,2));

% Black channel which has 0 components as all of pixel image levels

lena_1=cat(3,lena_ch1,lena_ch2,lena_ch3);

lena_2=cat(3,lena_ch1,lena_ch3,lena_ch2);

lena_3=cat(3,lena_ch2,lena_ch1,lena_ch3);

lena_4=cat(3,lena_ch2,lena_ch3,lena_ch1);

lena_5=cat(3,lena_ch3,lena_ch1,lena_ch2);

lena_6=cat(3,lena_ch3,lena_ch2,lena_ch3);

subplot(1,factorial(size(lena,3)),1); imshow(lena_1);

subplot(1,factorial(size(lena,3)),2); imshow(lena_2);

subplot(1,factorial(size(lena,3)),3); imshow(lena_3);

subplot(1,factorial(size(lena,3)),4); imshow(lena_4);

subplot(1,factorial(size(lena,3)),5); imshow(lena_5);

subplot(1,factorial(size(lena,3)),6); imshow(lena_6);

Answer 1

[Walter Roberson]

Put the channels into a cell array:

lena_ch = num2cell(lena, [1 2]);

Now you can loop over the rows of

indices = perms(1:3)
numrows = size(indices,1); %6 rows

using each row as indices into lena_ch