% EXTRACTFIELDS  - Separates fields from a video frame.%% Function to separate fields from a video frame% and (optionally) interpolate intermediate lines% for each field.%% Usage: [f1, f2] = extractfields(im,interp)%%   f1 and f2 are the odd and even fields%   im is the frame to be split%   interp is an optional string `interp' indicating%   whether f1 and f2 should be padded out with interpolated%   lines.% Copyright (c) 2000 Peter Kovesi% School of Computer Science & Software Engineering% The University of Western Australia% http://www.csse.uwa.edu.au/% % Permission is hereby granted, free of charge, to any person obtaining a copy% of this software and associated documentation files (the "Software"), to deal% in the Software without restriction, subject to the following conditions:% % The above copyright notice and this permission notice shall be included in % all copies or substantial portions of the Software.%% The Software is provided "as is", without warranty of any kind.% May 2000function [f1, f2] = extractfields(im,interpstring)        if nargin < 2	interpstring = 'nointerp';    end        if (ndims(im)==3),    % A colour image - Transform red, green, blue components separately	[f1r, f2r] = extractFieldsI(im(:,:,1), interpstring);	[f1g, f2g] = extractFieldsI(im(:,:,2), interpstring);	[f1b, f2b] = extractFieldsI(im(:,:,3), interpstring);		% Reform colour image for field 1	f1 = repmat(uint8(0),[size(f1r),3]);	f1(:,:,1) = uint8(round(f1r));	f1(:,:,2) = uint8(round(f1g));	f1(:,:,3) = uint8(round(f1b));		% Reform colour image for field 2	f2 = repmat(uint8(0),[size(f2r),3]);	f2(:,:,1) = uint8(round(f2r));	f2(:,:,2) = uint8(round(f2g));	f2(:,:,3) = uint8(round(f2b));	    else         % Assume grey scale image	[f1, f2] = extractFieldsI(im,interpstring);    end        function  [f1, f2] = extractFieldsI(im,interpstring)        [rows,cols] = size(im);    im = double(im);    if nargin==2	if strcmp(interpstring, 'interp')	    interp = 1;	elseif strcmp(interpstring, 'nointerp')	    interp = 0;	else	    warning(['unknown interpolation option - no interpolation is' ...		     ' being used']);	    interp = 0;	end    else	interp = 0;    end            if mod(rows,2) == 1	rows = rows-1;        % This ensures even and odd fields end up with     end                     % the same No of rows        f1 = im(1:2:rows,:);   % odd lines    f2 = im(2:2:rows,:);   % even lines        if interp	f1 = interpfields(f1,'odd');	f2 = interpfields(f2,'even');    end