Image Processing: Zoom in, process image, zoom out

I am writing a GUI in which a user can apply some basic image processing (adjust brightness, contrast and thresholding) to an image file. Right now, I'm trying to figure out how to do a simple three step operation like:

1) Zoom in on image

2) process image (i.e. thresholding), while zoomed

3) Zoom out of image

I already managed to program steps 1) and 2), and it works quite good. Unfortunately I can't zoom out of the image after processing it. This is the code:

1) Zoom in

function zoomIn_OnCallback(hObject, eventdata, handles)
% hObject    handle to zoomIn (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

global origXLim origYLim
zoomIn = zoom;

% save original axes limits
origXLim = get(handles.procAxes,'XLim');
origYLim = get(handles.procAxes,'YLim');

 % get axes limits after zooming
set(zoomIn,'ActionPostCallback',@mypostcallback);

function mypostcallback(obj,evd)
global newXLim newYLim

newXLim = get(evd.Axes,'XLim');
newYLim = get(evd.Axes,'Ylim');

2) Image processing (here thresholding with a slider)

% --- Executes on slider movement.
function threshSlider_Callback(hObject, eventdata, handles)
% hObject    handle to threshSlider (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'Value') returns position of slider
%        get(hObject,'Min') and get(hObject,'Max') to determine range of slider
global newXLim newYLim
% get slider value
value = get(hObject, 'Value');

% display Slider value
set(handles.threshValue, 'String', num2str(value));

% thersholding (selfwritten function)
handles.newImg = threshold(handles.procImg, value, handles.color);

% display on axes for processed image
axes(handles.procAxes);
imshow(handles.newImg);
set(handles.procAxes, 'XLim', newXLim);
set(handles.procAxes, 'YLim', newYLim);

% update handles structure
guidata(hObject, handles);

I actually know, that I can't zoom out to the original size of the image, because I have set the limits of the axes that display the image to the new values 'newXLim' and 'newYLim'. But I just don't know an other way to keep the "zoomed in" state while applying the thresholding to the image. Is there maybe another way to do this?

Answer 1

[Walter Roberson]

Instead of using imshow at that point, update the Cdata property of the image object. You should not need to set the axis xlim or ylim when you do that.

[Phillip Probst]

Thank you very much, Walter!

This actually solves everything and shortens my code. Just perfect!

Best Regards

Phillip

[Maria Avila]

I have been trying to do a very similar program to yours and I have been having troubles with the zoom. I have been able to perform zoom on a set of images with the code you gave, but I have been having troubles understanding what do you mean by "update the Cdata property of the image object". How can I do that?

Answer 2

[Image Analyst]

Attached is the Mathworks demo for zooming.