The matrices rgb and imag1 have same values,same dimensions but different class.But while displaying images imag1 and rgb are different.Why is it so?

clc;
clear all;
close all;
imag1=imread('lena.jpg');
subplot(1,2,1);
imshow(imag1);
v=rgb2gray(imag1);
r=1;
[rows, columns] = size(v);
N=rows;
M=columns;
subplot(1,3,1);
imshow(v);
if(M~=N)
    I=imresize(v,[M,M]);
else
    I=v;
    end
x(1)=0.8;
r=1;
c=0.505;
for i=1:((M*M)*8)
    x(i+1)=4*(x(i)*(1-x(i))*x(i));
    if(x(i)>c)
      w(i)=0;
    else if(x(i)<=c)
      w(i)=1;
        end
    end
end   
 while r<((M*M)+1)
    for i=1:M
    for j=1:M
        k(r)=I(i,j);
        l(r)=k(r);
        r=r+1;
        end
    end
 end
r=1;
for r1=1:(M*M)
    for c1=1:8
        if(r<(((M*M)+1)*8))
        z=de2bi(l(r1),8);
        b(:,r)=z(c1);
        r=r+1;
        end
    end
end
%%%%Cipher creation%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
for i=1:(M*M*8)
 encrypt(i)=bitxor(w(i),b(i));
end
%%%%%%%%%%binary to decimal
k=1;
l=1;
j=1;
    while(l<=(M*M))
            k1=encrypt(k:(j*8));
            cipher=bi2de(k1);
            c(l)=cipher;
            k=(j*8)+1;
            j=j+1;
            l=l+1;
    end
    %%%%%string to image
    l1=1;
   while (l1<(M*M)+1)
       for i=1:M
           for j=1:M
               v2(i,j)=c(l1);
               l1=l1+1;
           end
       end
   end
   subplot(1,3,2);
   imshow(v2);
%    v3=im2uint8(v2);
%    results = NPCR_and_UACI(v,v3); 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%DECRYPTION%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   for i=1:(M*M*8)
       decrypt(i)=bitxor(encrypt(i),w(i));
   end
   l=1;
   jj=1;
   kk=1;
   while(l<=(M*M))
            k2=decrypt(kk:(jj*8));
            cipher1=bi2de(k2);
            c1(l)=cipher1;
            kk=(jj*8)+1;
            jj=jj+1;
            l=l+1;
    end
    l2=1;
   while (l2<(M*M)+1)
       for i=1:M
           for j=1:M
               d(i,j)=c1(l2);
               l2=l2+1;
           end
       end
   end
    rgb=d(:,:,[1 1 1]);
    subplot(1,3,3);
    imshow(rgb);
  end

This is the code.Now the problem is that rgb is 256*256*3

whose matrix values are same as matrix of original image.But I'm

unable to get the image as such.

Answer 1

[Stephen23]

"Why is it so?"

Because the different classes get treated differently.

The output from imread is (most likely) of class uint8.

imshow assumes that uint8 image data is between 0 and 255, and that double image data is between 0 and 1. This has been explained multiple times on this forum:

http://www.mathworks.com/matlabcentral/answers/88934-images-don-t-show-with-imshow-after-converting-them-to-double

http://www.mathworks.com/matlabcentral/answers/109199-png-image-created-in-matlab-shows-up-as-all-black-in-imshow

So you need to convert the double data to the range [0,1], or convert the image to uint8 using im2uint8, or use the second optional input to specify the input data range:

imshow(I,[0,255])