error in decryption code saying not enough input arguments

the code is for decrypting a text from an encrypted image .

    clc;
    close all;
    clear all;
    img=imread('enc2.gif');
    imshow('enc2.gif');
    img1=imread('C:\Users\Anushree Bhatt\Desktop\cd1\Major\desert1.jpg');
    img1=img1(:,:,3);
    [p,q,r]=size(img);

    for i=1:q
        disp(img(1,1));
        disp(img1(1,1));
        disp(img(1,i)-img1(1,i));
       if (img(1,i)-img1(1,i)==0)
        break;
       end
      text(i)=(img(1,i)-img1(1,i)+96);
    end

    len=size(text);
    k=len(1,2);
    text1=zeros(1,k);
    for i=1:k
        m=text(i)
        for j=1:7
            if (j-1)>0
                a(j-1)=rem(m,2);
            else
                a(7)=rem(m,2);
            end
            m=floor(m/2);
            disp(m);
            if m==1
                a(m)=1;
                break;
            end
        end
        for j=0:6
            text1(i)=text1(i)+a(j+1)*(2^j);
        end
    end

    text1=char(text1);
    disp (text1);
    X=('The encrypted text is');
    disp(X);
    disp(text1);

the error is at m=text(i) saying not enough input arguments.i shall post the code for encryption if required.

Answer 1

[Walter Roberson]

Do not name a variable "text" as that conflicts with the MATLAB graphic function text()

Your code looks through row 1 of the two images, looking for the first column at which the two have the same value. If it happens that the very first location is the same, then your code will never execute the assignment you have currently coded as

text(i)=(img(1,i)-img1(1,i)+96);

and since you do not initialize that variable, the variable would not exist when you go to use it inside the next "for" loop.

You also need to take into account that your imread() is likely returning uint8 values, and that if you subtract a larger uint8 value from a smaller then the result you get is 0, not negative.

disp(uint8(3) - uint8(7));   %is going to give you 0
disp(uint8(7) - uint8(3));   %is going to give you 4
disp(uint8(3) - uint8(7) + 1);  %is going to give you 1, because the subtraction gives 0 and you add 1 to that
disp(double(uint8(3)) - double(uint8(7)));  %is going to give you -4

[Anushree Bhatt]

Can you help me fix this , how can I change the code in order to fix the problem ? Should I subtract img1 from img ?

[Walter Roberson]

Change

img=imread('enc2.gif');

to

img = double(imread('enc2.gif'));

and likewise when you read in the other image. That will eliminate the problem with subtraction clipping at 0.

And before your "for i" loop, use

text = [];

in order to initialize "text". Then if you "break" before assigning a value into the variable, it will still exist and size() of it will be [0 0]

[Anushree Bhatt]

now there is no error but the code is not showing the encrypted text .can i post the code of encryption here , you could refer

[Anushree Bhatt]

i have followed the decryption algorithm just in reverse of the encryption algorithm,it is still not returning the encrypted string.

[Anushree Bhatt]

    clc;
    close all;
    clear all;
    img=imread('C:\Users\Anushree Bhatt\Desktop\cd1\Major\desert1.jpg');
    figure,imshow(img),title('Original Image');
    [a,b,c]=size(img);
    img3=img(:,:,3);

    str=input('Enter a string: ', 's');
    str=double(str);
    len=size(str);
    k=len(1,2);
    str1=zeros(1,k);
    for i=1:k
        m=str(i);
        for j=1:7
            a(j+1)=rem(m,2);
            m=floor(m/2);
            %disp(m);
            if m==1
                a(m)=1;
                break;
            end
        end
        for j=0:6
            str1(i)=str1(i)+a(j+1)*(2^j);
        end
    end
    disp(str1);

    for i=1:size(str1,2)
        str1(i)=str1(i)-96;
    end
    text=zeros(1,size(str1,2)+1);
    text=str1;
    text(size(str1,2)+1)=0;
    for i=1:size(str1,2)+1
        img3(1,i)=img3(1,i)+text(i);
    end

    imwrite(img3,'enc2.gif');

    figure,imshow(img3),title('Encrypted Image');

this is the code for encryption.

[Anushree Bhatt]

now its showing a wrong encrypted text, i entered the string 'WELCOME' and on decryption it is showing 'GEEEGEE'

[Walter Roberson]

Have you looked at dec2bin() or de2bin() and their reverse functions? or bitset() and bitget() ? They might be a bit more robust than your current code.

[Anushree Bhatt]

Yes , that is not the problem , the problem seems to be at rotating the binary number of ascii code by one digit

[Anushree Bhatt]

thank you for the help , my code worked . :)