MATLAB: Need help with accessing every block of image for calculating svd of these blocks

image processingImage Processing Toolbox

Hi everyone, i have done coding for my project related to image forensics. But now i am stuck at finding svd of each block of the image. Here is my code snippet.
clc;
clear;
close all;
%%read image
im = [];
[FileName,PathName] = uigetfile({'*.png';'*.jpeg';'*.bmp';'*.gif';'*.jpg'},'Select the Image file');
if~(isequal(FileName,0)|| isequal(PathName,0))
    m= fullfile(PathName,FileName);
    im = imread(m);
end
img = im2double(rgb2gray(im));
[f1, f2] = size(img);
%%1- Apply Stationary wavelet transform up to specified level "L" to the gray image.
disp('1-Applying SWT to grayscale image ');
disp('1-Wavelet.....');
LL{1} = img;
 k = 1;
    [LL{k}, LH{k}, HL{k}, HH{k}] = swt2(LL{k},1,'db6');
 %%2- Divide the image into overlapping blocks.
 disp('2- Dividing the image into overlapping blocks of size 16x16');
 block_size = 16;
 patches = im2col(LL{1}(:,:,1),[block_size,block_size],'sliding'); %breaks image into blocks
 [m1, n1] = size(patches);
 num_blocks = (1:n1);
%%3- Apply SVD to each block
 disp('3- Feature extraction by computing the SVD Transform of each 16x16 window');
so i am no getting how to access each block and apply SVD to each block. Plz help me if anybody knows regarding this.

Best Answer

function [Ses, AllSes] = svdimg(IMG)
    if ndims(IMG) ~= 2
        error('Cannot handle RGB images');
    end
    AllSes = blockproc(IMG, [8 8], @(block) svdd(double(block.data)), 'Border', [4 4], 'Trim', false);
    [r, c] = size(AllSes);
    rb = floor(r/16);
    lor = mod(r, 16);
    cb = floor(c/16);
    loc = mod(c, 16);
    Ses = mat2cell(AllSes, [16 * ones(1,rb), lor], [16 * ones(1,cb), loc]);
end
function S = svdd(M)
   [U, S, V] = svd(M);
end
First output will be a cell array of SVD diagonals of 16 x 16 sliding blocks overlapping by 4 on each edge. Second output is the matrix of results not broken up into blocks.
Note: zero padding is used at the edges. For example the first block processed might look like
     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0
     0     0     0     0   156   159   158   155   158   156   159   158   157   158   158   159
     0     0     0     0   160   154   157   158   157   159   158   158   158   160   155   156
     0     0     0     0   156   159   158   155   158   156   159   158   157   158   158   159
     0     0     0     0   160   154   157   158   157   159   158   158   158   160   155   156
     0     0     0     0   156   153   155   159   159   155   156   155   155   157   155   154
     0     0     0     0   155   155   155   157   156   159   152   158   156   158   152   153
     0     0     0     0   156   153   157   156   153   155   154   155   157   156   155   156
     0     0     0     0   159   159   156   158   156   159   157   161   162   157   157   159
     0     0     0     0   158   155   158   154   156   160   162   155   159   161   156   161
     0     0     0     0   155   154   157   158   160   160   159   160   158   161   160   160
     0     0     0     0   154   157   157   157   156   155   159   154   159   158   161   158
     0     0     0     0   152   150   155   154   152   156   157   156   157   154   157   159
Here 4 rows of padding left and top have been used automatically.
Related Question