Matlab GUI: Problems while using imfreehand() - matlab

Question

I have applied Canny edge detection on am image and now want to crop a part of it for further procession. I have created 4 axes with the tags axes1, axes2, axes3 and axes4. I want to display the image first in axes1, then the edge detected again in axes1. Finally the cropped image is to be displayed in axes3 and the image after removal of holes in axes4.
I am including a sample code which recreates the problem:
function varargout = samp_GUI(varargin)
% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name', mfilename, 'gui_Singleton', gui_Singleton, 'gui_OpeningFcn', #samp_GUI_OpeningFcn, 'gui_OutputFcn', #samp_GUI_OutputFcn, 'gui_LayoutFcn', [] , 'gui_Callback', []);
if nargin && ischar(varargin{1})
gui_State.gui_Callback = str2func(varargin{1});
end
if nargout
[varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT
% --- Executes just before samp_GUI is made visible.
function samp_GUI_OpeningFcn(hObject, eventdata, handles, varargin)
handles.output = hObject;
guidata(hObject, handles);
% --- Outputs from this function are returned to the command line.
function varargout = samp_GUI_OutputFcn(hObject, eventdata, handles)
varargout{1} = handles.output;
% --- Executes on button press in browse.
function browse_Callback(hObject, eventdata, handles)
[filename pathname] = uigetfile({'*.jpg';'*.bmp'},'File Selector');
handles.myImage = strcat(pathname, filename);
axes(handles.axes1);
imshow(handles.myImage)
im=imread(handles.myImage);
bw3=im2bw(im,0.3); %threshold value taken as 0.3
BW3=edge(bw3,'canny');
edge_im = BW3;
axes(handles.axes1);
imshow(BW3);
h=imfreehand(handles.axes1);
M=~h.createMask();
I(M) = 0;
axes(handles.axes2);
imshow(I);title('Cropped Image')
I = bwareaopen(I, 50);
axes(handles.axes3);
imshow(I),title('Removed Holes');
% save the updated handles object
guidata(hObject,handles);
When i execute the code in a .m file, it runs perfectly with different images opening in different windows but when the same code is run for the GUI, blank images are problems. I do not seem understand where the problem lies.

Answer 1

I think that you're suffering from some form of copy/paste issue. If you look at the line in your code where I(M) = 0 this doesn't really make sense (given your example) since I is not defined.
MATLAB will not throw any errors at this point though, because it's perfectly valid to create a matrix in this way; however, doing so actually produces a row vector rather than the image you're wanting.
>> M = logical(eye(100));
>> size(M)
ans =
100 100
>> clear I
>> I(M) = 0;
>> size(I)
ans =
1 10000
I imagine what you wanted to do was to apply the mask to your image (im) in which case you should get what you want. I have provided an example below (not sure what you're trying to display in axes1).
load mri
img = double(D(:,:,12));
im = img ./ max(img(:));
figure
handles.axes1 = subplot(2,2,1);
handles.axes2 = subplot(2,2,2);
handles.axes3 = subplot(2,2,3);
handles.axes4 = subplot(2,2,4);
bw3=im2bw(im,0.3); %threshold value taken as 0.3
BW3=edge(bw3,'canny');
edge_im = BW3;
axes(handles.axes1);
imshow(BW3);
h=imfreehand(handles.axes1);
M=~h.createMask();
% Assign im to I to ensure proper cropping.
I = im;
I(M) = 0;
axes(handles.axes3);
imshow(I);title('Cropped Image')
M_noholes = bwareaopen(M, 50);
I(M_noholes) = 0;
axes(handles.axes4);
imshow(I),title('Removed Holes');
If you provide more information it will be easier to help you figure out what you need.