I need help with my GUI

I need some help with my following code:

(1) I my following code when push the button the start button the camera starts , while running I want to capture image from the cam after each 5 seconds and want to save that fram in a folder.

(2) when push stop button the cam should stop capturing frames too.

function varargout = MyFERApp(varargin)
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
                   'gui_Singleton',  gui_Singleton, ...
                   'gui_OpeningFcn', @MyFERApp_OpeningFcn, ...
                   'gui_OutputFcn',  @MyFERApp_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 MyFERApp is made visible.
function MyFERApp_OpeningFcn(hObject, eventdata, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
% varargin   command line arguments to MyFERApp (see VARARGIN)

% Choose default command line output for MyFERApp
handles.output = hObject;

% Update handles structure
guidata(hObject, handles);

% UIWAIT makes MyFERApp wait for user response (see UIRESUME)
% uiwait(handles.figure1);
handles.output = hObject;
imaqreset
handles.cam = webcam(1);
guidata(hObject, handles);

% --- Outputs from this function are returned to the command line.
function varargout = MyFERApp_OutputFcn(hObject, eventdata, handles) 
% varargout  cell array for returning output args (see VARARGOUT);
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Get default command line output from handles structure
varargout{1} = handles.output;


% --- Executes on button press in Start_Camera_button.
function Start_Camera_button_Callback(hObject, eventdata, handles)
% hObject    handle to Start_Camera_button (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
global KeepRunning;
KeepRunning=1;
while KeepRunning
    cam = handles.cam;
    data = snapshot(cam);
    imshow(data, 'Parent', handles.axes1);
    hold on
    
end
guidata(hObject, handles);
 
% --- Executes on button press in Stop_Camera_Button.
function Stop_Camera_Button_Callback(hObject, eventdata, handles)
% hObject    handle to Stop_Camera_Button (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
global KeepRunning;
KeepRunning=0;
guidata(hObject, handles);
% --- Executes on button press in Delete_Camera_Button.
function Delete_Camera_Button_Callback(hObject, eventdata, handles)
% hObject    handle to Delete_Camera_Button (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
cam = handles.cam;
delete (cam);
clear cam;
guidata(hObject, handles);

[Ben Cunningham]

Could you briefly elaborate on what the specific problems you are trying to solve are?

ie what is your code doing now vs what you want it to do.

[saeeda saher]

I am trynig to run cam and on live streem want to take snapshots with 5 seconds of pause , and want to save those images in to the folder in image formate. I want 2 buttons here to work, one for starting the camera and the other for stoping the camera; between start and stop the camera should take snapshots and save them unless stop button is pressed

[Walter Roberson]

What error message are you seeing? Or describe the difference between what you are getting and what you want to get.

Answer 1

[Ben Cunningham]

See the 'interruptible' property of callbacks in app designer - e.g. here under the heading 'Callback execution control'.

You need to create an opportunity for the Stop_Camera_Button_Callback to interrupt the while loop in Start_Camera_button_Callback. The sentence of interest is:

"The interruption occurs at the next point where MATLAB processes the queue, such as when there is a drawnow, figure, uifigure, getframe, waitfor, or pause command."

In other words a drawnow command can provide an oppurtunity for your stop button to interrupt the execution of the while loop to set the global variable, then when the while loop resumes KeepRunning will evaluate false (0).

Without drawnow, the stop button will wait until the previous callback is finished - which never occurs since your while loop will spin forever.

In your case you want the while loop to execute with a 5 second pause so the pause command might be more applicable.

ie

while KeepRunning
    cam = handles.cam;
    data = snapshot(cam);
    imshow(data, 'Parent', handles.axes1);
    hold on
    pause(5) % Pause for 5 seconds and allow opportunity for Stop Button Callback to interrupt
end

Depending what you are after then the timer based implementation suggested by Geoff Hayes may be preferable.

Answer 2

[Geoff Hayes]

saeeda - rather than using a loop to capture your images, consider using a timer that executes every five. (By the way, a problem with the while loop is that it might not be interruptible and so even if you press the stop button, the loop will continue. You can get around this by calling an appropriate function, see Interrupt Callback Execution for details.)

In your start function, you could do something like

function Start_Camera_button_Callback(hObject, eventdata, handles)

handles.timer = timer('Name','MyTimer',               ...
                      'Period',5,                     ... 
                      'StartDelay',0,                 ... 
                      'TasksToExecute',inf,           ... 
                      'ExecutionMode','fixedSpacing', ...
                      'TimerFcn',{@timerCallback,handles.figure1}); 
guidata(hObject,handles);
start(handles.timer);

The above will start your timer and its callback will fire every five seconds. We save the timer object to the handles structure so that we can stop it later.

Your timer callback will look something like

function [] = timerCallback(~,~,guiHandle)
if ~isempty(guiHandle)
    % get the handles
    handles = guihandles(guiHandle);
    data = snapshot(handles.cam);
    imshow(data, 'Parent', handles.axes1);
    % save your image to file with imwrite
end

You will need to define how you want to save the file (i.e. format, name, location).

Finally, your stop pushubtton callback will be

function Stop_Camera_Button_Callback(hObject, eventdata, handles)
if isfield(handles, 'timer')
    stop(handles.timer);
    handles = rmfield(handles, 'timer');
    guidata(hObject, handles);
end

The above is untested but should give you an idea of what you can do.

[saeeda saher]

great, you understood it what I wanted. Thank You

[saeeda saher]

I am getting this error

Error while evaluating TimerFcn for timer 'MyTimer'

Reference to non-existent field 'cam'.

[Geoff Hayes]

The error message is telling you that the handles structure (or something else) doesn't have the 'cam' field. When is the cam object created? Have you assigned it to the handles object and called guidata(hObject, handles)? It looks like you did this in the opening function of your GUI but perhaps you have changed something since posting that initial code...