Looping through GUI imagesc, but greyscale and reverse?

I currently have a code that looped through multiple different netcdf files to display (for example, 14 different images). The following is my code within the "opening function" function within the GUI:

% Choose default command line output for test
handles.output = hObject;
handles.files = dir('C:\Users\Micheal\Documents\MATLAB\Test2\*.netcdf');
for i = 1:length(handles.files)

    filenames = [handles.files(i,1).name];
    ncid = netcdf.open(filenames,'NC_NOWRITE');
    [varname, xtype, varDimIDs, varAtts] = netcdf.inqVar(ncid,0);

Then a whole bunch of calculations are presented which are not included here

    % handles.X{i} = Zfilenames(i,1).Z;
    netcdf.close(ncid)   
imagesc(handles.X{i}');
colormap('jet')
title(filenames)
  end
handles.index = 1;
Cek(hObject,eventdata,handles)
% Update handles structure
guidata(hObject, handles);

I then have my two buttons, back and next which will allow me to loop through the images

    % % --- Executes on button press in Back.
function Back_Callback(hObject, eventdata, handles)
% hObject    handle to Back (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
handles.output = hObject;
handles.index = handles.index - 1;
Cek(hObject, eventdata, handles);
imshow(handles.X{handles.index},[]);
guidata(hObject, handles);
% --- Executes on button press in Next.
function Next_Callback(hObject, eventdata, handles)
% hObject    handle to Next (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
handles.output = hObject;
handles.index = handles.index + 1;
Cek(hObject, eventdata, handles);
imshow(handles.X{handles.index},[]);
guidata(hObject, handles);
function Cek(hObject, eventdata, handles)
handles.output = hObject;
n = length(handles.files);
if handles.index > 1,  set(handles.Back,'enable','on');
else                           set(handles.Back,'enable','off'); end
if handles.index < n, set(handles.Next,'enable','on');
else                           set(handles.Next,'enable','off'); end
guidata(hObject, handles);

What happens is that my GUI presents the last image within my list of filenames with the correct orientation, colormap, and title. However, when I select "Next", everything becomes greyscale, with the incorrect orientation, and no title. Where am I missing the updated axes and colormap and title options? Any help would be greatly appreciated.

Answer 1

[Walter Roberson]

I do not know offhand about the orientation, but the title and grayscale problems are obvious.

You are using imshow() to draw each image. imshow() is a "higher level graphics function". Like all of the higher level graphics functions, it checks the state of "hold on", and if that is not set then it does a cla() before adding the image. The cla() removes the active title and colormap.

You should do the imshow() once right at the beginning, and record the handle of the image() object returned. After that, at each step forward or back you should set the image object CData to the new content. That will update the image without changing the title or colormap. Chances are that you will also be wanting to record the handle returned by title() and update its String property to reflect the image being viewed.

By the way, your code to read the images has a bug. You should change

handles.files = dir('C:\Users\Micheal\Documents\MATLAB\Test2\*.netcdf');
for i = 1:length(handles.files)

      filenames = [handles.files(i,1).name];

to something more like

projectdir = 'C:\Users\Micheal\Documents\MATLAB\Test2'
handles.files = dir( fullfile(projectdir, '*.netcdf') );
for i = 1:length(handles.files)

    filenames = fullfile(projectdir, handles.files(i,1).name );

Otherwise you are asking netcdf to read from files that might be in some other directory that it does not know about.

[Simpson]

Thank you for the feedback, and your recommendation for fixing my code.

I actually want to use "imagesc", as I have in the top of my code. I have replaced all of the "imshow" in my callback buttons to "imagesc", accordingly.

However, I am a little confused by what you mean by including the imshow at the beginning. Furthermore, where exactly would I put in the handles.axes or handles.image function? I have tried in several different places but nothing has changed?

[Image Analyst]

imagesc() juse scales the images, so up to there it's the same as passing [] into imshow(grayImage, []). However then imagesc() applied some weird default colormap, whereas imshow() does not, and that forces you to apply a gray scale colormap or else apply a colormap that makes sense. For that reason, I don't use imagesc(). imshow() is now in base MATLAB, so any particular reason why you're using imagesc and colormap, rather than imshow()? By the way with the last release or two of MATLAB you have to pass the axes handle into colormap().

[Walter Roberson]

I, on the other hand, resist using imshow() as it does weird things like resizes the figure.

[Walter Roberson]

% Choose default command line output for test
projectdir = 'C:\Users\Micheal\Documents\MATLAB\Test2';

files = dir( fullfile(projectdir, '*.netcdf') );

for i = 1 : length(files)
    filenames{i} = fullfile( projectdir, files(i).name );
    ncid = netcdf.open( filenames{i}, 'NC_NOWRITE');
    [varname, xtype, varDimIDs, varAtts] = netcdf.inqVar(ncid, 0);

      %Then a whole bunch of calculations are presented which are not included here

      handles.X{i} = Zfilenames(i,1).Z;
      netcdf.close(ncid)

     %no point in displaying the intermediate images as only the last one will be left on the screen

end

handles.filenames = filenames;

handles.index = 1;

handles.OutImage = imagesc( handles.X{1}.' );
ax = ancestor(handles.OutImage, 'axes');
colormap(ax, 'jet')

[~, basename, ~] = fileparts( filenames{i} );
handles.OutTitle = title(ax, basename);

guidata(hObject, handles);

Cek(hObject,eventdata, handles)

% --- Executes on button press in Back.
function Back_Callback(hObject, eventdata, handles)
% hObject    handle to Back (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

    handles.index = handles.index - 1;
    set(handles.OutImage, 'CData', handles.X{handles.index}.' );
    [~, basename, ~] = fileparts( handles.filenames{handles.index} );
    set(handles.OutTitle, 'String', basename);
    guidata(hObject, handles);

    Cek(hObject, eventdata, handles);

% --- Executes on button press in Next.
function Next_Callback(hObject, eventdata, handles)
% hObject    handle to Next (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

    handles.index = handles.index + 1;
    set(handles.OutImage, 'CData', handles.X{handles.index}.' );
    [~, basename, ~] = fileparts( handles.filenames{handles.index} );
    set(handles.OutTitle, 'String', basename);
    guidata(hObject, handles);

    Cek(hObject, eventdata, handles);

function Cek(hObject, eventdata, handles)

    states = {'off', 'on'};

    n = length(handles.filenames);

    set(handles.Back, 'enable', states{(handles.index > 1) + 1});
    set(handles.Next, 'enable', states{(handles.index < n) + 1});