Embed a secret information into the color image and decode.

%% embed secret
% Import the base image
Base = imread('peppers.png');
imshow(Base);title('Base Image')
% Import the message image and convert to binary image 
Message=imread('secret_spy.jpg');
Msg=imbinarize(rgb2gray(Message));
% Resize the message and base image to same size 
Msg=imresize(Msg,size(Base(:,:,1)));
% Select a bit plane and change it to our message signal 
New=Base;
New(:,:,1)=bitset(New(:,:,1),1,Msg);
% Save the image file 
imshow(New);title('Image with hidden message')
%montage(Base,New);
imwrite(New,'MsgIm.bmp');
clc;

I used this code to embed the secret and now I am trying to decode this.

I used this below but failed. How should I decode it? I can't use predefined function.

%% Decode
% Import the image with hidden image 
Im = imread('gray_peppers_secret.png');
% Extract the bitplane of the message signal 
MessageImage=bitget(Im(:,:,1),1);
% Visualize the message 
imshow(logical(MessageImage));

[Walter Roberson]

It works when I test -- making sure that I read from the same file that I wrote out (which you do not do.)

[Soomin Lee]

Oh shoot. Thank you for pointing that out. It was a dumb mistake :/

Is there a way to do this without making the secret image into binary image? I want to keep the color as it is.

[Walter Roberson]

You have numel(Base) * 1 bits available to encode into.

You have numel(Message) * 8 bits that you need to encode.

So you need to resize(Message) to get Msg such that numel(Msg)*8 == numel(Base)... so numel(Msg) = numel(Base)/8 .

But what resizing factor do you use to accomplish that? You need

imresize(Message, [size(Base,1)/A, size(Base,2)/B])

such that A*B == 8 . But you cannot distribute the 8 equally as A == B == sqrt(8) because sqrt(8) is irrational, and you can be sure that the resulting image will not have exactly the right number of locations.

What are the factors? Well, you can do (1,8) or (2,4) or (4,2) or (8,1) ... are those acceptable ?

Or... you can figure out a way that you do not use every available location to encode the image.