error trying to read files

Hi

I'm struggling with the current code i'm translated from idl, basically I've got a list of darkfield images named dark1,dark2,dark3,dark4,dark5. and a list of flatfield images named flat1,flat2,flat3,flat4,flat5 i'm trying to create a loop on the darkfield images and flatfield images and calculate their average using the code below. i get an error when the code starts a loop for k = 1:ndark

filesAndFolders = dir(workdir); 

filesInDir = filesAndFolders(~([filesAndFolders.isdir]));  % Returns only the files in the directory                    

j=1;

for i=1:length(filesInDir)
    if(strfind(filesInDir(i).name,'flat'))
        flatlist{j} = filesInDir(i).name;
        j=j+1;
    end
end

nflat = numel(flatlist);

%darklist = file_search(workdir,'dark*')

j=1;
for i=1:length(filesInDir)
    if(strfind(filesInDir(i).name,'dark'))
        darklist{j} = filesInDir(i).name;
        j=j+1;
    end
end

ndark = numel(darklist);

dark = zeros(ysize,xsize);
flat = zeros(ysize,xsize);

for k = 1:ndark  
    imtemp = imread(darklist{k});
    dark = dark+double(imtemp)./ndark;

     % ;Average dark images
  end 

for k = 1:nflat
    imtemp = imread(flatlist{k});
     flat = flat+double(imtemp)./nflat;

      %;Average flat image
  end 

flatsub = flat-dark;
flatsub(find(flatsub <= 0)) = 1;

Answer 1

[Walter Roberson]

   flatinfo = dir( fullfile(workdir, 'flat*') );
   flatlist = fullfile( workdir, {flatinfo.name} );
   nflat = numel(flatlist);

   darkinfo = dir( fullfile(workdir, 'dark*') );
   darklist = fullfile( workdir, {darkinfo.name} );
   ndark = numel(darklist);

   flat = zeros(ysize,xsize);
   for K = 1 : nflat
     imtemp = imresize( imread(flatlist{k}), [ysize, xsize] );
     flat = flat + double(imtemp);
   end
   flat = flat ./ nflat;

   dark = zeros(ysize,xsize);
   for K = 1 : ndark
     imtemp = imresize( imread(darklist{k}), [ysize, xsize] );
     dark = dark + double(imtemp);
   end
   dark = dark ./ ndark;

flatsub = flat - dark;
flatsub(flatsub <= 0) = 1;

But are you sure that you want to set the zero / negative areas to 1 and not to 0? To me it would make more sense to use

flatsub = max(0, flat - dark);

which would use 0 for places that would have been negative.