can any one provide me the code for dividing the image 306x204 into blocks of size i,e windows of size 17x17

i want to know the code for dividing the image into blocks or windows of size 17x17

[Romil Shah]

im = rand(306,204);
for k=1:12*18
  for i=1:306/18
    for j=1:204/12
        newim(i,j,k)=im(i*18,j*12);
    end
  end
end

Does this clear your query? MATLABhelper.com

Answer 1

[Azzi Abdelmalek]

im=rand(306,204)
[n,m]=size(im)
[ii,jj]=ndgrid(1:17:n,1:17,m)
out=arrayfun(@(x,y) im(x:x+16,y:y+16),ii,jj,'un',0)

[kishore kumar]

clear all 
clc
close all 
I=(imread('wm.gif'));
I=imresize(I,[306 204]);
I=I/max(max(I));
I=double(I);
[m n]=size(I);
% I=magic(4);
% [m n]=size(I);
for i=1:18
for    j=1:12
%      num=2i+j-2;
filter_gradient = fspecial('sobel'); 
               %to get x gradient
               if((i-1>0)&&(j-1)>0)
           gx((i-1)*17:(i)*17,(j-1)*17:(j)*17) = filter2(filter_gradient,I((i-1)*17:(i)*17,(j-1)*17:(j)*17));
  %to get y gradient
   filter_gradient = transpose(filter_gradient);
    gy((i-1)*17:(i)*17,(j-1)*17:(j)*17)= filter2(filter_gradient,I((i-1)*17:(i)*17,(j-1)*17:(j)*17));
               end
end
end
figure;imshow(gx)
[g1 g2]=imgradientxy(I,'sobel')
figure;imshow(g1)

%%ridge orientation
gxy(1:m,1:n)=0;gxx(1:m,1:n)=0;gyy(1:m,1:n)=0;

for i=9:m-9
  for j=9:n-9

        for i1=-8:+8
            for j1=-8:+8
                gxy(i,j)=gxy(i,j)+((gx(i+i1,j+j1)).*(gy(i+i1,j+j1)));
                gxx(i,j)=gxx(i,j)+gx(i+i1,j+j1).^2;

                gyy(i,j)=gyy(i,j)+gy(i+i1,j+j1).^2;

            end
        end
        Q(i,j)=pi/2+0.5*(atan2((2*gxy(i,j)),((gxx(i,j)-gyy(i,j))))); 
    end
end

so far i have done upto this , i have to calculate ridge orientation and gradients using block wise can you help in writing the code for and am not sure whether mine is correct or not

[Azzi Abdelmalek]

This is not your original question

[kishore kumar]

yeah actually my whole process goes on dividing the blocks and then proceeding further and the code which you have given it was showing 18x17 but i want 17x17

[Azzi Abdelmalek]

im=rand(306,204)
[n,m]=size(im)
n1=n/17
m1=m/17
[ii,jj]=ndgrid(1:n1:n,1:m1:m)
out=arrayfun(@(x,y) im(x:x+n1-1,y:y+m1-1),ii,jj,'un',0)
size(out)

[Image Analyst]

What does "proceeding further" mean, and why is blocproc() - the built-in function meant for this kind of thing - no good? blockproc will both split up, AND process each block with your custom code, all in one single line of code.

[Azzi Abdelmalek]

Kumar, if you have Image Processing Toolbox you can use blockproc function

Example, if you want to calculate the mean of each block

im=rand(306,204)
[n,m]=size(im)
n1=n/17
m1=m/17
out=blockproc(im,[n1,m1],@(x) mean(mean(x.data)))

[kishore kumar]

sir can you tell me the code with out using this inbuilt functions (blockproc,arrayfun).. and actaully i want to calculate the gradient of each pixel in each block

Answer 2

[Image Analyst]

See the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_split_an_image_into_non-overlapping_blocks.3F

If you want to do something with the blocks, then use blockproc(). See attached demos.