why this code is not working *(steganography)

function [Eslam] = stegancoder(img,msg,enc_key)

msgtype = ischar(msg);  

if msgtype == 1     
msg_tmp = double(msg);     
msg_D = num2str(length(msg_tmp));
msg_length = length(msg_D);
    c = 0;
if msg_length< 7
P_text = 7 - msg_length;
for c = 1:P_text
msg_D = horzcat('0',msg_D);
end
msg_head = horzcat('t',msg_D);
msg_tmp_head = horzcat(msg_head,msg_tmp);
end

else
msg = im2uint8(msg);   

msg_tmp = rgb2gray(msg); 
   [H_M1,H_N1] = size(msg_tmp);
    H_M = num2str(H_M1);
    H_N = num2str(H_N1);
    D_M = length(H_M);
    D_N = length(H_N);
    P_M = 0; P_N = 0;
    c = 0;

if D_M < 4
        P_M = 4 - D_M;
for c = 1:P_M
            H_M = horzcat('0',H_M);
end
end
    c = 0;

if D_N < 4
        P_N = 4 - D_N;
for c = 1:P_N
            H_N = horzcat('0',H_N);
end
end
msg_head = horzcat(H_M,H_N);
msg_tmp_head = msg_head;

      b = 0;  k = H_M1;
  for b = 1:k
  msg_tmp_head = horzcat(msg_tmp_head,msg_tmp(b,:));
  end

end
msg_enc = bitxor(uint8(msg_tmp_head),uint8(enc_key));

msg_enc_set = dec2bin(msg_enc, 8);
img_good =double(img);
img_prep = im2uint8(img_good);

redm = 1; greenm = 1; bluem = 1;  
redn = 1; greenn = 1; bluen = 1;

[maxM,maxN] = size(img_prep);
c = 0;

run_time = length(msg_enc_set);

for c = 1:run_time;
tmp_code = msg_enc_set(c,:);
if str2double(tmp_code(1)) == 0
img_prep(redm,redn,1) = bitand(img_prep(redm,redn,1),uint8(254));
else
img_prep(redm,redn,1) = bitor(img_prep(redm,redn,1),uint8(1));
end

redm = redm + 1;

if redm>maxM
redn = redn + 1;
redm = 1;
end
if str2double(tmp_code(2)) == 0
img_prep(greenm,greenn,2) = bitand(img_prep(greenm,greenn,2),uint8(254));
else
img_prep(greenm,greenn,2) = bitor(img_prep(greenm,greenn,2),uint8(1));
end

greenm = greenm + 1;
if greenm>maxM
greenn = greenn + 1;
greenm = 1;
end
if str2double(tmp_code(3)) == 0
img_prep(bluem,bluen,3) = bitand(img_prep(bluem,bluen,3),uint8(254));
else
img_prep(bluem,bluen,3) = bitor(img_prep(bluem,bluen,3),uint8(1));
end

bluem = bluem + 1;
if bluem>maxM
bluen = bluen + 1;
bluem = 1;
end
if str2double(tmp_code(4)) == 0
img_prep(bluem,bluen,3) = bitand(img_prep(bluem,bluen,3),uint8(254));
else
img_prep(bluem,bluen,3) = bitor(img_prep(bluem,bluen,3),uint8(1));
end

bluem = bluem + 1;
if bluem>maxM
bluen = bluen + 1;
bluem = 1;
end
if str2double(tmp_code(5)) == 0
img_prep(greenm,greenn,2) = bitand(img_prep(greenm,greenn,2),uint8(254));
else
img_prep(greenm,greenn,2) = bitor(img_prep(greenm,greenn,2),uint8(1));
end

greenm = greenm + 1;
if greenm>maxM
greenn = greenn + 1;
greenm = 1;
end
if str2double(tmp_code(6)) == 0
img_prep(redm,redn,1) = bitand(img_prep(redm,redn,1),uint8(254));
else
img_prep(redm,redn,1) = bitor(img_prep(redm,redn,1),uint8(1));
end
redm = redm + 1;
if redm>maxM
redn = redn + 1;
redm = 1;
end
if str2double(tmp_code(7)) == 0
img_prep(redm,redn,1) = bitand(img_prep(redm,redn,1),uint8(254));
else
img_prep(redm,redn,1) = bitor(img_prep(redm,redn,1),uint8(1));
end
redm = redm + 1;
if redm>maxM
redn = redn + 1;
redm = 1;
end
if str2double(tmp_code(8)) == 0
img_prep(greenm,greenn,2) = bitand(img_prep(greenm,greenn,2),uint8(254));
else
img_prep(greenm,greenn,2) = bitor(img_prep(greenm,greenn,2),uint8(1));
end

greenm = greenm + 1;
if greenm>maxM
greenn = greenn + 1;
greenm = 1;

end

Eslam = img_prep;       
end

[Geoff Hayes]

ahmad - please elaborate on what you mean by why this code is not working. What are you expecting it to do that it isn't? Are you observing any errors with your input image, message, and key? Please include an example of your image (greyscale or rob), message, and key.

[ahmad nasser]

when i enter any image to use it as a cover image .by writing x=stegancoder('IMG_4675.JPG','ahmad',42) it gives me this message as an error

??? Attempted to access img_prep(1,1,2); index out of bounds because size(img_prep)=[1,12,1].

Error in ==> stegancoder at 87 img_prep(greenm,greenn,2) = bitor(img_prep(greenm,greenn,2),uint8(1));

Answer 1

[Image Analyst]

This link will allow you to find out why your code is not working: http://blogs.mathworks.com/videos/2012/07/03/debugging-in-matlab/

Answer 2

[Walter Roberson]

You are passing in the name of an image, but you never imread() the image, so the array you are processing as "img" is the string that is the file name rather than being the file content.