fopen gives -1. How to open??

My current work involves image processing. Just recently I have been looking at archived files from the early 2000's. The problem is that these images are stored as *.FILT, *.filt or *.im.... To my knowledge these filetypes where created by a past colleague inorder to save the image data with a text header (information about the image). My problem now is that these images cannot be opened as the software is far out of date.

I have written a small code to convert these files into *.bmp as follows:

clear all 
close all

% Prompt for image file 
[image_file image_file_path image_file_filterindex] = uigetfile({'*.FILT;*.filt;*.im;*'}, 'Select image for conversion to *.bmp','MultiSelect','On');

if iscell(image_file) ==1
    for n=1:length(image_file)
        [pathstr, name, ext] = fileparts(image_file{n});
        file_id = fopen(image_file{n})
        if file_id ~= -1
            header = fread(file_id,8192,'char');
            image = fread(file_id,[1024,1024],'uint16',0,'b');
            % image = fread(file_id,[1024,1024],'int16',0,'n');
            image = image./max(image(:));
            fclose('all');
            imwrite(image, [image_file_path name '_2_uint16_b' '.bmp'], 'bmp');    
    end
    end
elseif iscell(image_file) ==0
    [pathstr, name, ext] = fileparts(image_file);
    file_id = fopen(image_file)
    if file_id ~= -1
        header = fread(file_id,8192,'char');
        image = fread(file_id,[1024,1024],'uint16',0,'b');
        % image = fread(file_id,[1024,1024],'int16',0,'n');
        image = image./max(image(:));
        fclose('all');
        imwrite(image, [image_file_path name '_2_uint16_b' '.bmp'],'bmp');
    end
end

My problem is that fopen gives -1 most of the time and so I cannot even open the file. However I have just recently found by running the program a few times on the same file that sometimes fopen gives -1 and sometimes it gives a valid id and the conversion goes through... Is there something wrong with fopen?? Any ideas??

Answer 1

[Jan]

fopen replies -1 when it does not find the file. You can test this:

file_id = fopen(image_file{n});
if file_id == -1
  if exist(image_file{n}, 'file')
    error('Cannot open existing file: %s', image_file{n});
  else
    error('Missing file: %s', image_file{n});
  end
end

Unfortunately this does not give the correct warning, the you try to open a folder, because exist(S, 'file') checks for folders also. Anyhow, it should help to find the problem.

[Brenden]

You are right, with your code it gives error:

??? Error using ==> imgcon2 at 34
Missing file: 30205a0_a2_06a5.FILT

How then do I get Matlab to find the file? Is it a problem with the folder names? Or do I first have to use 'uigetdir' to open the directory and then use 'uigetfile' to open the files? Shouldn't 'uigetfile' save the path information so it can open the file?

[Jan]

I guess that this is a folder problem. uigetfile does not manipulate the path, but replies the pathname and the filename only. You can either use uigetdir or cd to specify the path. Then fullfile helps to create full path names for the files, such that they are found reliably.

[Brenden]

Thank you Jan. You where right it was not reading the file path. I changed the code as follows:

file_id = fopen([image_file_path '/' image_file{n}]);

[Brenden]

I have one more question. In the above code I read the data with

image = fread(file_id,[1024,1024],'uint16',0,'b');

where i specify the size of the image as [1024,1024]. Is there anyway to have matlab calculate what size the image is from the file?