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?

Question

Veera Kalyani S 2017-1-9

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/319595-the-matrices-rgb-and-imag1-have-same-values-same-dimensions-but-different-class-but-while-displaying

编辑： Stephen23 2017-1-10

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.

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Answer 1

Stephen23 2017-1-9

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/319595-the-matrices-rgb-and-imag1-have-same-values-same-dimensions-but-different-class-but-while-displaying#answer_249869

编辑：Stephen23 2017-1-10

在 MATLAB Online 中打开

"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])