Basically there are main
four mediums in which steganography is to be carried out. These four mediums
are Text, Image, Audio/Video and Protocol. Image stegnography plays
important role in stenographic field. Image stegnography is divided into Spatial
domain and Transform domain. Spatial domain further divided into simple LSB
(least significant bit) substitution, LSB matching and PVD (pixel value
difference). Transform domain is one of most significant domain in image
stegnography.
In transform domain DCT (discrete cosine transform) and DWT (discrete wavelet transform) are used. DCT belongs to a lossy compression field. DWT is used for both lossy as well as lossless compression.
In transform domain DCT (discrete cosine transform) and DWT (discrete wavelet transform) are used. DCT belongs to a lossy compression field. DWT is used for both lossy as well as lossless compression.
Basic Types of Stegnography
Spatial
Domain Steganography:
Basically spatial domain is divided into LSB (least significant
bit) substitution, LSB matching and PVD (pixel value difference). In this
domain all operations are directly concerned with the image pixels.
Least Significant Bit (LSB) Substitution:
The principle involved in this method is to replace all LSB
bits of pixels of the cover image with secret bits. This method embeds the
fixedlength secret bits in the same fixed length LSBs of pixels. Although this
technique is simple, it generally causes noticeable distortion when the number
of embedded bits for each pixel exceeds three.
LSB Substitution (a) Image having size
2*2, (b) Binary format of image (a), (c) Binary secret data, (d) LSB
substitutionembedding (c) into (b), (e) Final image after substitution
Above figures shows you
detailed information about LSB substitution method. Figure (a) is a original
image having size of 2*2. Figure (b) shows binary format of image. Figure (c)
is a secret image; this image will be embedded into (b). Figure (d) is a stego
object in which secret data is embedded. Embedded data is indicated by bold
font and finally figure (e) is a modified image after embedding process.
Advantages
1. This method
having high embedding capacity. This method directly replaces LSBs of all
pixels of image.
2. Second
advantage of this method is that it is easily implementable. Algorithms proposed
for LSB substitution method are very easy for implementation.
Limitations
1. This method
is easily detectable. Steganalysis is very easy because LSBs of each pixels are
directly replaced by secret bits.
2. Quality of stego image is very poor because LSBs of each pixel is
replaced. Quality of stego image drastically decreases if more than one secret
bit embedded into cover image pixels.
MATLAB
Program:
Function of Message Embedding:
function
out_emd_img=embed1(img,sec_msg)
%This function embeds message into cover image.....
%output=====
%out_emd_img=message embedded image
%input======
%img=input image
%sec_msg=secrete message
[r c p]=size(img);
len=length(sec_msg);
j1=1;
count=1;
if(length(sec_msg)<=(r*c))
for i=1:r
for j=1:c
if(count<=len)
img(i,j)=bitset(img(i,j),1,sec_msg(1,j1));
j1=j1+1;
count=count+1;
end
end
end
out_emd_img=img;
else
disp('Opeartion is Invalid')
end

Test Application:
clc
a=[1 2 3;2 3 4;3 4 5];% Cover Image Matrix
s=[1 0 1 1 1 1 0];% Secrete Data
out_emd_img=embed1(a,s);

Output of the Program:
you are doing good job
ReplyDeleteThank you so much
DeleteDo you have a matlab program for retrieve or extract LSB hidden message?
ReplyDelete