how to divide a color image into blocks?

sir, my project is watermarking into a colored image(divided into 128x128 dimension 4 blocks) using dwt and svd technique.

I have written the following code for the full color image dwt and svd.

clc
close all

%original image

org_img=imread('lena.jpg');
figure;
imshow(org_img);
title('Original color image');
[h_LL,h_LH,h_HL,h_HH]=dwt2(org_img,'haar');
img=h_LL;
red1=img(:,:,1);
green1=img(:,:,2);
blue1=img(:,:,3);
[U_imgr1,S_imgr1,V_imgr1]= svd(red1);
[U_imgg1,S_imgg1,V_imgg1]= svd(green1);
[U_imgb1,S_imgb1,V_imgb1]= svd(blue1);

%watermark imagee

org_img=imread('fruits.jpg');
figure;
imshow(org_img);
title('Watermark image');
[w_LL,w_LH,w_HL,w_HH]=dwt2(org_img,'haar');
img_wat=w_LL;
red2=img_wat(:,:,1);
green2=img_wat(:,:,2);
blue2=img_wat(:,:,3);
[U_imgr2,S_imgr2,V_imgr2]= svd(red2);
[U_imgg2,S_imgg2,V_imgg2]= svd(green2);
[U_imgb2,S_imgb2,V_imgb2]= svd(blue2);

% watermarking by SVD

S_wimgr=S_imgr1+(0.10*S_imgr2);
S_wimgg=S_imgg1+(0.10*S_imgg2);
S_wimgb=S_imgb1+(0.10*S_imgb2);

wimgr = U_imgr1*S_wimgr*V_imgr1';
wimgg = U_imgg1*S_wimgg*V_imgg1';
wimgb = U_imgb1*S_wimgb*V_imgb1';

wimg=cat(3,wimgr,wimgg,wimgb);
newimage_LL=wimg;

%output 

rgb2=idwt2(newimage_LL,h_LH,h_HL,h_HH,'haar');
imwrite(uint8(rgb2),'Watermarked.jpg');
figure;imshow(uint8(rgb2));title('Watermarked Image');

kindly tell me how to divide this host image 'lena.jpg' into 4 blocks of size 128x128 using either a looping technique or mat2cell. also dierct me if i can use functions to access differnt blocks of the image.

regards

Yashi

[TUSHAR MURATKAR]

i have one question. after running this code i got cellarray of size 2x2. This i understood . but each cell is of size 192x56 . why it is like this why not 128x128 ? any help will be appreciated.

[Walter Roberson]

The above code does not create cell arrays. The code I posted does.

What does size(org_img) show for you?

Answer 1

[Walter Roberson]

img4x4 = mat2cell( org_img, size(orig_img,1)/2 * ones(1,2), size(orig_img,2)/2 * ones(1,2), size(orig_img,3) );

[yashi gautam]

thank you sir for the response. I have one more request Can you tell me how can i access different blocks of img4x4.

[Walter Roberson]

img4x4{1,1}    %upper left
img4x4{1,2}    %upper right
img4x4{2,1}    %lower left
img4x4{2,2}    %lower right

I should have called it img2x2 intead of img4x4 though ;-)

[yashi gautam]

Thank you sir.. True.. img2x2 was more logical :) thanks a ton for the help. regards yashi