Importing a "Large (2.5GB)" TIFF file with 'imread' function

Hello,

The end goal of this code is to calculate surface roughness from a large TIFF file where the z value is the greyscale. Here I am trying to read the TIFF image.

function open_image_Callback(hObject, eventdata, handles)

[filename, pathname]=uigetfile('*.*','MultiSelect','on','Open images');
cd(pathname)
[N,M]=size(filename);
   image=imread(char(filename{1}));
    [n,m,p]=size(image);
     if p==3
         image=rgb2gray(image);
         data(:,:,1)=double(image);
         data(:,:,M)=double(image);
     else
         data(:,:,1)=double(image);
         data(:,:,M)=double(image);
     end
 for i=2:M
        image=imread(char(filename{i}));
       [n,m,p]=size(image);
     if p==3
         image=rgb2gray(image);
         data(:,:,i-1)=double(image);
     else
         data(:,:,i-1)=double(image);
     end
 end

but I get the error :

Brace indexing is not supported for variables of this type.

Error in roughnessGUI>open_image_Callback (line 86)

image=imread(char(filename{1}));

Error in gui_mainfcn (line 95)

feval(varargin{:});

Error in roughnessGUI (line 45)

gui_mainfcn(gui_State, varargin{:});

Error in matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)roughnessGUI('open_image_Callback',hObject,eventdata,guidata(hObject))

Error while evaluating Menu Callback.

Thanks for your help!

Answer 1

[Jan]

The error message means, that filename is a char vector. Then the index {1} would work with a cell string, which would be replied by uigetfile, if multiple files are selected.

If only 1 file is selected, convert it to a cell string also, which is scalar in this case:

[filename, pathname] = uigetfile('*.*','MultiSelect','on','Open images');
filename = cellstr(filename);  % Remains a cell string if it is one already
M = numel(filename);

Instead of using cd() to change the current folder, it is much safer to use absolute path names:

image = imread(fullfile(pathname, filename{1}));

Note: filename{1} replies a char already. There is no need to convert this by char() again.

In your code data(:,:,1) is overwritten in all cases. A simplified version:

function open_image_Callback(hObject, eventdata, handles)
[filename, pathname] = uigetfile('*.*','MultiSelect','on','Open images');
filename = cellstr(filename);  % Remains a cell string if it is one already
M = numel(filename);
for k = 1:M
   img = imread(fullfile(pathname, filename{i}));
   p   = size(image, 3);
   if p == 3
      img = rgb2gray(img);
   end
   
   index = k - 1;
   if index == 0
       index = M;
   end
   data(:, :, index) = double(img);
end
end

Using "image" as name of a variable shaddows an important Matlab function.

Answer 2

[DGM]

This problem will occur when you only select one file. In that case, the variable filename is a single char array instead of a cell array of char arrays. You could conditionally test for this event and fix it prior to using the variable

if ischar(filename)
    filename={filename};
end

or something like that.