2.9 Reading SUN Raster Image Files into MATLAB

You can use MATLAB's file I/O to correctly read in the SUN raster image files. Basically, you need to strip off the header and interpret it. Then read in the colormap, if there is one, and finally read in the data.

SUN raster files are supported by a variety of SUN applications. One of the most popular applications is XV, which lets you view, edit, and save several different formats. A good reference is Chapter 11 of Graphics File Formats written by David Kay and John Levine, published by Windcrest/McGraw-Hill, or see the SUN documentation.

The following is an M-file that will read standard SUN raster files. It does not work with compressed files.

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function [X,map]=rastread(filename);
%RASTREAD Read a BMP SUN raster file
%  [X,MAP]=RASTREAD('filename') reads the file 
%  'filename' and returns the indexed image X and
%  associated colormap MAP. If no extension is given 
%  for the filename, the extension '.rast' is assumed.
%
%  See also: BMPREAD, BMPWRITE, GIFREAD, HDFREAD, 
%            PCXREAD, TIFFREAD, XWDREAD.
%  Jeffery J. Faneuff  March 29, 1994
%  Copyright (c) 1994 by The MathWorks, Inc.
if nargin~=1 | isstr(filename)~=1
  error('Requires a string filename as an argument.');
end;
if (isempty(findstr(filename,'.'))==1)
  filename=[filename,'.ras'];
end;
fid=fopen(filename,'rb','l');
if (fid==-1)
  disp('The file should have an extension of .ras ');
  error(['Error opening ',filename,'.']);
end;
magicnum=fread(fid,1,'uint32');
if (magicnum~= hex2dec('59a66a95'))
  fclose(fid);
  error('Not a SUN raster file.');
end;
width = fread(fid,1,'uint32');
height = fread(fid,1,'uint32');
depth = fread(fid,1,'uint32');
length = fread(fid,1,'uint32');
type = fread(fid,1,'uint32');
maptype = fread(fid,1,'uint32');
maplength = fread(fid,1,'uint32');
if (type~=1)
  fclose(fid);
  error('Not a standard encoded SUN raster file. ');
end;
if (maptype==1)
  rawmap = fread(fid,maplength,'uchar');
  map = reshape(rawmap,maplength/3,3);    % make a Nx3
                                          % colormap
  map = map./255;                         % normalize 
                                          % to 255
end
X = fread(fid,[width, height],'uchar');
fclose(fid);