my project related to steganography using 3 level discrete wavelet transform. mery question is that what is the size of secret image before and after embedding? is there any loss of data during extraction.i am converting jpg image to bw with64*64

si = double(handles.si);
alpha = 0.05;
for i = 1:4:size(LL3,1)
    for j = 1:4:size(LL3,2);
        block = LL3(i:i+3,j:j+3);
        block1 = si(i:i+3,j:j+3);
        emb(i:i+3,j:j+3) = ((1-alpha)*block)+(alpha*block1);
    end
end
axes(handles.axes5);
imshow(emb,[]);
title('emb image');

% IDWT
out3 = idwt2(emb,LH3,HL3,HH3,'haar');
out2 = idwt2(out3,LH2,HL2,HH2,'haar');
out1 = idwt2(out2,LH1,HL1,HH1,'haar');
axes(handles.axes5);
imshow(out1,[]);
title('Stego G panel image');
handles.out1 = out1;
% Update handles structure
guidata(hObject, handles);
helpdlg('Process completed');

Answer 1

[Walter Roberson]

The size of the secret image that is embedded is the same size of image that is extracted.

Steganography always has loss of data, unless the output is larger than the original. The challenge of steganography is to make the loss unnoticable even to programs that are analyzing the image to see if there is something hidden in it.