Way around using rasread with a uint 16 sun raster file

So I downloaded the PNM tool box from the file exchange, which included rasread. I'm trying to read in and display sun raster files but when I try to use the program, i get this error message: "invalid bitdepth: 16". Is there a way to convert the sun raster file to not be uint 16 or is there a way to modify the program?

[Benjamin]

using info = imfinfo(file_name)

I'm able to get:

info =

Filename: [1x131 char]

FileModDate: '21-Apr-2011 11:58:30'

FileSize: 46432544

Format: 'RAS'

FormatVersion: []

Width: 3552

Height: 6536

BitDepth: 16

ColorType: 'indexed'

FormatSignature: 1.5041e+009

Length: 46431744

Type: 1

MapType: 1

MapLength: 768

If this helps at all

Answer 1

[Walter Roberson]

I am not able to find any documentation that supports the possibility of 16 bits per pixel for Sun raster files. The values I can find documented are 1, 8, 24, and 32. See http://www.fileformat.info/format/sunraster/egff.htm . Note that this is the total number of bits per pixel including all channels.

[Benjamin]

Yeah, that's what I was afraid of. And if I remember correctly, those values (1, 8, 24, and 32) are the ones listed for RAS files in IMREAD() as well. Thanks Walter

[Benjamin]

Do you think there would be a way to read the RAS file in as binary and display it from there?

[Walter Roberson]

I would think it likely that the existing program could be modified. That isn't something I have time to look at this week.

[Benjamin]

Walter, So i found this function randomly which is different from rasread, but when i use it, i get this error: Not a SUN raster file. When clearly i do in fact have sun raster files.

 % 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);