function [R,G,B] = ppmread(filename)
%PPMREAD Read a PPM (portable pixmap) file from disk.
%
% [R,G,B] = PPMREAD('FILENAME') reads the file 'FILENAME' and returns
% the RGB image in the matrices R, G, and B.
%
% [X,MAP] = PPMREAD('FILENAME') reads the file 'FILENAME' and returns
% the indexed image X and associated color map MAP.
%
% If file name has no suffix, '.ppm' is used.
%
% PPMREAD can also read PGM and PBM images, but the output is always
% returned as if the image read was a PPM image.
%
% See also: PPMWRITE, PBMREAD, PBMWRITE, PGMREAD, PGMWRITE.
% Author: Peter J. Acklam
% Time-stamp: 1998-04-15 21:26:37
% E-mail: jacklam@math.uio.no (Internet)
% URL: http://www.math.uio.no/~jacklam
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Check number of input arguments.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
error( nargchk( 1, 1, nargin ) );
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Identify output arguments.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
nargsout = nargout;
if ( nargsout == 3 )
isindexed = 0;
elseif ( nargsout == 2 )
isindexed = 1;
else
error( 'Wrong number of output arguments.' );
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Check filename.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
if ( ~ischar( filename ) | isempty( filename ) )
error( 'File name must be a non-empty string' );
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Add suffix to file name if necessary.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
k = [ find( filename == filesep ) ];
if isempty(k)
k = 0;
else
k = max(k);
end
if all( filename(k+1:end) ~= '.' )
filename = [ filename '.ppm' ];
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Open input file for reading.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
fid = fopen( filename, 'r' );
if ( fid == -1 )
error( [ 'Can''t open file ''' filename ''' for reading.' ] );
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Identify file type.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Look for magic number.
[ magic, offset, msg ] = pnmmagic( fid );
if ~isempty( msg )
fclose( fid );
error( msg );
end
if ( magic == 'P1' ) | ( magic == 'P4' ) % Bitmap.
fclose( fid );
if isindexed
[ R, G ] = pbmread( filename ); % Indexed bitmap.
else
R = pbmread( filename ); % Intensity bitmap.
G = R;
B = R;
end
return
elseif ( magic == 'P2' ) | ( magic == 'P5' ) % Graymap.
fclose( fid );
if isindexed
[ R , G ] = pgmread( filename ); % Indexed graymap.
else
R = pgmread( filename ); % Intensity graymap.
G = R;
B = R;
end
return
elseif ( magic == 'P3' ) % Ascii encoded pixelmap.
isascii = 1;
elseif ( magic == 'P6' ) % Binary encoded pixelmap.
isascii = 0;
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Read image size and maximum pixel value.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
[ header_data, count ] = pnmgeti( fid, 3 );
if count < 3
fclose( fid ); % Close file.
error( 'File ended while reading image header.' );
end
cols = header_data(1); % Number of columns in image.
rows = header_data(2); % Number of rows in image.
maxval = header_data(3); % Maximum pixel value.
pixels = rows*cols; % Number of pixels in image.
values = 3*pixels; % Number of color values.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Read image data.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
if isascii % Ascii encoded image.
[ data, count, msg ] = pnmgeti( fid, values );
if ~isempty( msg )
fprintf( 2, 'Warning: %s\n', msg );
end
else % Binary encoded image.
%
% There should be a single byte of whitespace between the image
% header data and the pixel area. Skip it.
%
fseek( fid, 1, 0 );
[ data, count ] = fread( fid, values, 'uint8' );
if ( count < values )
disp( 'Warning: End of file reached too early.' );
end
end
fclose( fid ); % Close file.
rvals = floor( (count+2)/3 ); % Number of red values.
gvals = floor( (count+1)/3 ); % Number of green values.
bvals = floor( count /3 ); % Number of blue values.
if isindexed % Indexed pixelmap.
R = zeros( cols, rows ); % Initialize index matrix.
R(1:pixels) = 1:pixels; % Fill data into matrix.
R = R';
G = zeros( pixels, 3 ); % Initialize color map.
G(1:rvals,1) = data(1:3:3*rvals); % Insert red component.
G(1:gvals,2) = data(2:3:3*gvals); % Insert green component.
G(1:bvals,3) = data(3:3:3*bvals); % Insert blue component.
G = G/maxval; % Map values to [0,1] interval.
else % Intensity pixelmap.
R = zeros(cols,rows); % Initialize red component.
G = zeros(cols,rows); % Initialize green component.
B = zeros(cols,rows); % Initialize blue component.
R(1:rvals) = data(1:3:3*rvals); % Insert red component.
G(1:gvals) = data(2:3:3*gvals); % Insert green component.
B(1:bvals) = data(3:3:3*bvals); % Insert blue component.
R = R'/maxval; % Map values to [0,1] interval.
G = G'/maxval; % Map values to [0,1] interval.
B = B'/maxval; % Map values to [0,1] interval.
end
