col2im.m

function a = col2im(b,block,mat,kind)
%COL2IM Rearrange matrix columns into blocks.
%   A = COL2IM(B,[M N],[MM NN],'distinct') rearranges each column of B into a
%   distinct M-by-N block to create the matrix A of size MM-by-NN.  If B =
%   [A11(:) A21(:) A12(:) A22(:)], where each column has length M*N, then A =
%   [A11 A12; A21 A22] where each Aij is M-by-N.
%
%   A = COL2IM(B,[M N],[MM NN],'sliding') rearranges the row vector B into a
%   matrix of size (MM-M+1)-by-(NN-N+1). B must be a vector of size
%   1-by-(MM-M+1)*(NN-N+1). B is usually the result of processing the output
%   of IM2COL(...,'sliding') using a column compression function (such as
%   SUM).
%
%   COL2IM(B,[M N],[MM NN]) is the same as COL2IM(B,[M N],[MM NN],'sliding').
%
%   Class Support
%   -------------
%   B can be logical or numeric.  A has the same class as B.
%
%   Example
%   -------
%       B = reshape(uint8(1:25),[5 5])'
%       C = im2col(B,[1 5])
%       A = col2im(C,[1 5],[5 5],'distinct')
%
%   See also BLOCKPROC, COLFILT, IM2COL, NLFILTER.

%   Copyright 1993-2015 The MathWorks, Inc.

%   I/O Spec
%   ========
%   IN
%      B          - any numeric class or logical
%      M,N,MM,NN  - double, integer
%   OUT
%      A          - same class as B

validateattributes(b,{'numeric' 'logical'},{'nonsparse'},mfilename,'B',1);
validateattributes(block,{'double'},{'integer' 'real' 'positive'},...
    mfilename,'[M N]',2);
validateattributes(mat,{'double'},{'integer' 'real' 'positive'},...
    mfilename,'[MM NN]',3);

if nargin < 4,          % Try to determine which block type is assumed.
    kind = 'sliding';
end

if ~ischar(kind),
    error(message('images:col2im:wrongBlockType'));
end

kind = [lower(kind) ' ']; % Protect against short string

if kind(1)=='d', % Distinct
    % Check argument sizes
    [m,n] = size(b);
    if prod(block)~=m, error(message('images:col2im:wrongSize')); end
    
    % Find size of padded A.
    mpad = rem(mat(1),block(1)); if mpad>0, mpad = block(1)-mpad; end
    npad = rem(mat(2),block(2)); if npad>0, npad = block(2)-npad; end
    mpad = mat(1)+mpad; npad = mat(2)+npad;
    if mpad*npad/prod(block)~=n,
        error(message('images:col2im:inconsistentSize'));
    end
    
    mblocks = mpad/block(1);
    nblocks = npad/block(2);
    aa = mkconstarray(class(b), 0, [mpad npad]);
    x = mkconstarray(class(b), 0, block);
    rows = 1:block(1); cols = 1:block(2);
    for i=0:mblocks-1,
        for j=0:nblocks-1,
            x(:) = b(:,i+j*mblocks+1);
            aa(i*block(1)+rows,j*block(2)+cols) = x;
        end
    end
    a = aa(1:mat(1),1:mat(2));
    
elseif kind(1)=='s', % sliding
    a = reshape(b,mat(1)-block(1)+1,mat(2)-block(2)+1);
else
    error(message('images:col2im:unknownBlockType', deblank(kind)))
    
end