Image encryption using chaotic map ,, what does this code mean ?

please this code is apart from a code which used to encrypt an image using logistic map key

i just want to know what does this line " [so , in ] = sort (x)" mean ??

and also i want explaination of the confusion step ,, please i need a help ,

tic
timg = img;
r = 3.62;
x(1) = 0.7;
row = size(img,1);
col = size(img,2);
s = row*col; 
for n=1:s-1
    x(n+1) = r*x(n)*(1-x(n));
end

[so,in] = sort(x);

%Start of Confusion
timg = timg(:);
for m = 1:size(timg,1)
    
    t1 = timg(m);
    timg(m)=timg(in(m));
    timg(in(m))=t1;
    
end

[Amr Muhammad]

Sort here means that:

you will generate a vector "In". The image vector will be confused and reconfused according to the values of "In" array.

For example:

Img=[4,2,5,6,9]

In=[3,5,1,4,2]

Imgencr=[Img(In(1) , Img(In(2) , Img(In(3) , Img(In(4) ,Img(In(5) ]

=[5, 9, 4, 6, 2 ]

Imgdecr[In(1)] = Imgencr[1] -> Imgdecr[3] = 5

Imgdecr[In(2)] = Imgencr[2] -> Imgdecr[5] = 9

Imgdecr[In(3)] = Imgencr[3] -> Imgdecr[1] = 4

Imgdecr[In(4)] = Imgencr[4] -> Imgdecr[4] = 6

Imgdecr[In(5)] = Imgencr[5] -> Imgdecr[2] = 2

Imgdecr=[ Imgdecr[1] , Imgdecr[2] , Imgdecr[3] , Imgdecr[4] , Imgdecr[5] ]

=[ 5, 9, 4, 6, 2 ]

is the same the original one (=img)

[Amr Muhammad]

The complete program used to confuse and reconfuse an image:

close all;
clear all;
clc;
tic
img = imread('cameraman.jpg');
timg=rgb2gray(img);
r = 3.62;
x(1) = 0.7;
row = size(timg,1);
col = size(timg,2);
s = row*col; 
for n=1:s-1
    x(n+1) = r*x(n)*(1-x(n));
end
[so,in] = sort(x);
tencr=reshape(timg,s,1);
%Start of Encryption
encrimg=[];
for m = 1:s
    encrimg(m)=tencr(in(m));
end
ImageEncr=reshape(encrimg,row,col);
figure
imshow(ImageEncr/255)
%Start of Decryption
tdecr=reshape(ImageEncr,s,1);
decrimg=[];
for m = 1:s
    decrimg(in(m))=tdecr(m);
end
ImageDecr=reshape(decrimg,row,col);
figure
imshow(ImageDecr/255)

[sajjad]

Its very nice code. I am als working on cryptography (Image Encryption and Decryption).

Answer 1

[Walter Roberson]

[so,in] = sort(x);

means that the vector x is to be sorted in ascending order, and that the sorted values are to be stored in the variable named "so". Furthermore, the variable named "in" is to be assigned indices. in(1) is to be assigned the index in x that so(1) came from, in(2) is where so(2) came from. The output is such that x(in)==so.

We cannot explain encryption algorithms here for legal reasons.

[Samaa Yasser]

thanks alot

can i ask you please , so if i want to change the equation to X,Y for example

Xn+1= 1+y(n)n-a*X(n)^2

Yn+1=b*X(n)

how can i re-write the line code [so,in] = sort(x); ??

Answer 2

[Image Analyst]

It means that the author never learned professional code writing techniques. Techniques like using descriptive variable names and putting in comments. If he had, you would have seen something like

% Sort x in ascending order and return the sorted x values and 
% the original location of the values in the unsorted, original vector.
[sortedValues, sortOrder] = sort(x, 'ascend');

and you probably would not have had to ask your question. Don't be like that bad programmer. Read these:

https://blogs.mathworks.com/loren/category/best-practice/?s_tid=Blog_loren_Category

https://www.mathworks.com/matlabcentral/answers/95695-is-there-a-document-describing-matlab-coding-standards-or-a-good-programming-guide-available