im2col function in MATLAB explanation

Let us suppose we have


A=[1 1;2 2]

1 1

2 2 ... ok


Now img2col syntax  == im2col(A,[m n],block_type)


Where block type = ('distinct','sliding')

distinct places 0's in the final output,,,for padding,

sliding,,repeats from the very first matrix element. after all elements read out.


Now..


Now [m n] -- very important ....


Number of Rows to show = M*N (if m=2 ,, n=2 then each column has 4 elements..)

and Number of element fetch to repeat is M in row...

That means,,


OUTPUT OF THIS - im2col(A,[2 2], 'sliding')

ans =

     1
     2
     1
     2


-- if  A=[1 1 1;2 2 2]

A =

     1     1     1
     2     2     2


then


im2col(A,[2 2], 'sliding')

ans = contains 4 rows....as 2*2 ...   and fetch 2 elements as M=2 here...

and sliding ,,so repeats after 6th element..

     1     1
     2     2
     1     1
     2     2


Now... next


 im2col(A,[3 2], 'distinct')


Here 3*2=6 elements in each row....and fetch 3 elements,,as it contains,,2 elements ,,add 0

and here is the output..

ans =

     1     1
     2     2
     0     0
     1     0
     2     0
     0     0


 Next


im2col(A,[2 3], 'distinct')

-- 6 elements,,,,,and fetch 2 from each column,,,

ans =

     1
     2
     1
     2
     1
     2


NEXT


 im2col(A,[2 4], 'distinct')

-- 8 rows...and fetch 2,,,from each column...

ans =

     1
     2
     1
     2
     1
     2
     0
     0


NEXT


 im2col(A,[4 2], 'distinct')
here 8 rows....and fetch 4 elements from each column,,,as we have 2 then add 2 zeros...to make 4 as needed.


ans =

     1     1
     2     2
     0     0
     0     0
     1     0
     2     0
     0     0
     0     0



Simple...Enjoy,, :)