%IM2COLSTEP Rearrange matrix blocks into columns.

%  B = IM2COLSTEP(A,[N1 N2]) converts each sliding N1-by-N2 block of the

%  2-D matrix A into a column of B, with no zero padding. B has N1*N2 rows

%  and will contain as many columns as there are N1-by-N2 neighborhoods in

%  A. Each column of B contains a neighborhood of A reshaped as NHOOD(:),

%  where NHOOD is a matrix containing an N1-by-N2 neighborhood of A.

%

%  B = IM2COLSTEP(A,[N1 N2],[S1 S2]) extracts neighborhoods of A with a

%  step size of (S1,S2) between them. The first extracted neighborhood is

%  A(1:N1,1:N2), and the rest are of the form A((1:N1)+i*S1,(1:N2)+j*S2).

%  Note that to ensure coverage of all A by neighborhoods,

%  (size(A,i)-Ni)/Si must be whole for i=1,2. The default function behavior

%  corresponds to [S1 S2] = [1 1]. Setting S1>=N1 and S2>=N2 results in no

%  overlap between the neighborhoods.

%

%  B = IM2COLSTEP(A,[N1 N2 N3],[S1 S2 S3]) operates on a 3-D matrix A. The

%  step size [S1 S2 S3] may be ommitted, and defaults to [1 1 1].

%

%  Note: the call IM2COLSTEP(A,[N1 N2]) produces the same output as

%  Matlab's IM2COL(A,[N1 N2],'sliding'). However, it is significantly

%  faster.

%

%  See also COL2IMSTEP, IM2COL, COUNTCOVER.

%  Ron Rubinstein

%  Computer Science Department

%  Technion, Haifa 32000 Israel

%  ronrubin@cs

%

%  August 2009