function spm_eeg_mask(S)
% Create a mask image for scalp-level contrasts
% FORMAT spm_eeg_mask(S)
%
% S         - input structure (optional)
% (optional) fields of S:
%    image        - file name of an image containing an unsmoothed 
%                   M/EEG data in voxel-space
%    timewin      - start and end of a window in peri-stimulus time [ms]
%    outfile      - output file name
%__________________________________________________________________________
% Copyright (C) 2008-2013 Wellcome Trust Centre for Neuroimaging

% Vladimir Litvak
% $Id: spm_eeg_mask.m 5308 2013-03-07 12:02:07Z guillaume $

SVNrev = '$Rev: 5308 $';

%-Startup
%--------------------------------------------------------------------------
spm('FnBanner', mfilename, SVNrev);
spm('FigName','M/EEG mask generation'); spm('Pointer','Watch');

%-Input parameters
%--------------------------------------------------------------------------
if ~nargin, S = []; end

if ~isfield(S, 'image')
    [S.image, sts] = spm_select(1, 'image', ...
        'Select an unsmoothed M/EEG image (in voxel-space)');
    if ~sts, return; end
end

if ~isfield(S, 'timewin')
    S.timewin = spm_input('start and end of window [ms or Hz]', '+1', 'r', '', 2);
end

if ~isfield(S, 'outfile')
    [f, p]    = uiputfile({'*.img;*.nii'}, 'Save output mask file as');
    if isequal(f,0) || isequal(p,0), return; end
    if isempty(spm_file(f, 'ext')), f = [f spm_file_ext]; end
    S.outfile = fullfile(p, f);
end

%-Create mask
%--------------------------------------------------------------------------
V = spm_vol(S.image);
Y = spm_read_vols(V);
Y = ~isnan(Y) & (Y~=0);

Nt = size(Y, 3);

begsample = V.mat\[0 0 S.timewin(1) 1]';
begsample = begsample(3);

endsample = V.mat\[0 0 S.timewin(2) 1]';
endsample = endsample(3);

if any([begsample endsample] < 0) || any([begsample endsample] > Nt)
    error('The window is out of limits for the image.');
end

[junk,begsample] = min(abs(begsample-(1:Nt)));
[junk,endsample] = min(abs(endsample-(1:Nt)));

if begsample > 1
    Y(: , :, 1:(begsample-1))   = 0;
end

if endsample < size(Y, 3)
    Y(: , :, (endsample+1):end) = 0;
end

%-Save mask image
%--------------------------------------------------------------------------
VM = struct(...
    'fname',   S.outfile,...
    'dim',     V.dim,...
    'dt',      [spm_type('uint8') spm_platform('bigend')],...
    'mat',     V.mat,...
    'pinfo',   [1 0 0]',...
    'descrip', sprintf('mask: [%d %d]',S.timewin));
VM = spm_create_vol(VM);

spm_write_vol(VM, Y);

%-Cleanup
%--------------------------------------------------------------------------
spm('FigName','M/EEG mask generation: done'); spm('Pointer','Arrow');