function image = readpgm(filename)
%READPGM Read a raw pgm file as a matrix
%
%        IMAGE = READPGM(FILENAME) reads the binary PGM image data from
%        the file named FILENAME and returns the image as a 2-dimensional
%        array of integers IMAGE. Assumes the file is a raw PGM file
%        containing 8-bit unsigned character data to represent pixel values.
%
% Matthew Dailey, 1997

% Open the file
fid = fopen(filename,'r');

% Parse and check the header information.  No # comments allowed.
A = fgets(fid);
if strcmp(A(1:2),'P5') ~= 1
  error('File is not a raw PGM');
end;
A = fgets(fid);
sizes = sscanf(A,'%d');
w = sizes(1);
h = sizes(2);
A = fgets(fid);
max = sscanf(A,'%d');
tlength = w*h;

if max ~= 255
 error('Cannot handle anything but 8-bit graymaps');
end; 

% Read the raw data
[v,count] = fread(fid,inf,'uchar');
if count ~= tlength
 error('File size does not agree with specified dimensions.');
end;

% Pack the column vector v into the image matrix
image = reshape(v,w,h)';

fclose(fid);