could you fix these codes?

    I=imread('filename'); 
    a1=I(1:8,1:8);
    a2=I(1:8,9:16);
    a3=I(1:8,17:24);
    a4=I(1:8,25:32);

    b1=I(9:16,1:8);
    b2=I(9:16,9:16);
    b3=I(9:16,17:24);
    b4=I(9:16,25:32);

c1=I(17:24,1:8);
c2=I(17:24,9:16);
c3=I(17:24,17:24);
c4=I(17:24,25:32);

d1=I(25:32,1:8);
d2=I(25:32,9:16);
d3=I(25:32,17:24);
d4=I(25:32,25:32);

could you tell me how to make it short? Thank you

Answer 1

[Jan]

Don't do this.

Hiding the index in the name of a variable is a bad programming pattern. It is much more efficient to use indices as indices:

img = reshape(a(1:32, 1:32), 8, 4, 8, 4);
img = permute(img, [1,3,2,4]);

Now you have img(:, :, 1, 1) instead of a1.

This is much faster, needs less memory, and allows to expand the method for millions of tiles easily.

[Tia]

wow..it's great.it's more efficient. thank you

[Image Analyst]

You may not even need to do that. It's possible that you do not need to even store the tiles at all. Do you? Why do these tiles need to be stored rather than just operated on and thrown away (reused)? Just operate on one tile at a time if you can - why store forever?

[Tia]

i try it. but it can't be back at 1D.. how do i get it? is it possible? or any ideas how to spilt it into 8x8pixels,but i want to manipulate each 8x8pixels,then store the tiles at all? thank you for your time

Answer 2

[Iman Ansari]

Hi. Use cell array:

I=imread('moon.tif');
C=mat2cell(I(1:32,1:32),8*ones(1,4),8*ones(1,4));
imshow(C{5},'InitialMagnification','fit')

C{5} or C{1,2} is a2 in your code.

[Tia]

i'm still confused. actually if i have these codes:

I=imread('filename');
ul=I(1:256,1:256);
ur=I(1:256,257:512);
ll=I(257:512,1:256);
lr=I(257:512,257:512);
s=[ul,lr;ur,lr];
figure,imshow(s)

but if i have 32x32pixels,then i divide it into 8x8blocks.i should to write long codes

    I=imread('filename'); 
    a1=I(1:8,1:8);
    a2=I(1:8,9:16);
    a3=I(1:8,17:24);
    a4=I(1:8,25:32);

    b1=I(9:16,1:8);
    b2=I(9:16,9:16);
    b3=I(9:16,17:24);
    b4=I(9:16,25:32);

c1=I(17:24,1:8);
c2=I(17:24,9:16);
c3=I(17:24,17:24);
c4=I(17:24,25:32);

d1=I(25:32,1:8);
d2=I(25:32,9:16);
d3=I(25:32,17:24);
d4=I(25:32,25:32);
s=[a1,b1,c2,d3;a3,b2,c3,d4;...]

i want to use 'for'. how can i get it? thanks for your fast answer

[Iman Ansari]

It's not good having variable named a1,a2,..., see this:

http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F

I=imread('moon.tif');
C=mat2cell(I(1:32,1:32),8*ones(1,4),8*ones(1,4));
imshow(C{5},'InitialMagnification','fit')

C in this code is:

C={a1,a2,a3,a4;b1,b2,b3,b4;c1,c2,c3,c4;d1,d2,d3,d4}

and for s:

s=[C{1,1} C{2,1} C{3,2} C{4,3};C{1,3} C{2,2} C{3,3} C{4,4};...]

[Tia]

thank you

Answer 3

[David Sanchez]

You can try as well something like this

I=imread(your_32x32_image_name);
division = 8; % set according to yuor needs
L = size(I,1)/division;
subI = cell( L,L );
for row=1:L
    for col=1:L
        subI{row,col} = I( (row:row*division),(col:(col*division)) );
    end
end

[Tia]

thank you